Download Service Literature 80MGF SERIES UNITS

80MGF
Corp. 9801−L2
Revised 08−2004
Service Literature
80MGF SERIES UNITS
80MGF series units are mid−efficiency gas furnaces
manufactured with tubular heat exchangers formed of aluminized or stainless steel. 80MGF units are available in
heating capacities of 45,000 to 140,000 Btuh and cooling
applications up to 5 tons. Refer to Engineering Handbook
for proper sizing.
Units are factory equipped for use with natural gas. A kit is
available for conversion to LPG operation. All 80MGF units
built proir to September 98 use electronic (direct spark) ignition. 80MGF−11 model units are equipped with the Lennox
SureLight ignition system. The 80MGFX unit meets the
California Nitrogen Oxides (NOx) Standards and California
Seasonal Efficiency requirements. All units use a redundant gas valve to assure safety shut−off as required by
A.G.A. or C.G.A.
The heat exchanger, burners and manifold assembly can
easily be removed for inspection and service by simply disconnecting gas, unplugging wiring harness and spark wires
and removing four screws holding the heat exchanger in
place. Then the heat exchanger slides out of the cabinet.
All specifications in this manual are subject to change.
Procedures outlined in this manual are presented as a recommendation only and do not supersede or replace local
or state codes. In the absence of local or state codes, the
guidelines and procedures outlined in this manual (except
where noted) are recommended only and do not constitute
code.
Units may be installed in upflow, downflow or horizontal
position. The heat exchanger is designed for upright or
horizontal use only. When the unit is installed in the downflow position, the heat exchanger is field removed and reinstalled so it is upright when the cabinet is inverted. No
field conversion is required when the unit is installed in the
horizontal position.
Introduction . . . . . . . . . . . . . . . . . . . . . . . .
Specifications . . . . . . . . . . . . . . . . . . . . . .
Blower Data . . . . . . . . . . . . . . . . . . . . . . .
Parts Identification . . . . . . . . . . . . . . . . . .
I Unit Components . . . . . . . . . . . . . . . . . .
II Installation . . . . . . . . . . . . . . . . . . . . . . .
1
2
5
7
9
19
TABLE OF CONTENTS
III Start Up . . . . . . . . . . . . . . . . . . . . . . . . .
Preliminary Seasonal Checks . . . . .
Heating Start Up . . . . . . . . . . . . . . . .
IV Heating System Service Checks . . .
V Typical Operating Characteristics . . .
VI Maintenance . . . . . . . . . . . . . . . . . . . .
VII Wiring and Sequence of Operation .
VIII SureLight Control Troubleshooting .
Page 1
19
20
20
20
22
24
26
40
© 1998 Lennox Industries Inc.
SPECIFICATIONS
Model No.
80MGF2(X)-45
80MGF2-60
80MGF3(X)-60
80MGF2-75
80MGF3(X)-75
Input Btuh (kW)
45,000 (13.2)
60,000 (17.6)
75,000 (22.0)
Output Btuh (kW)
36,900 (10.8)
49,200 (14.4)
61,700 (18.1)
A.F.U.E.
80.1%
80.5%
California Seasonal Efficiency
75.4%
76.4%
Flue size connection diameter in. (mm) round
75.9%
30 - 60 (17 - 33)
76.8%
45 - 75 (25 - 42)
.50 (125)
Gas Piping Size I.P.S. Natural or LPG/propane
1/2 (13)
in.
9x7
10 x 7
9x7
10 x 7
229 x 178
254 x 178
229 x 178
254 x 178
1/4 (187)
1/3 (224)
1/4 (187)
1/3 (224)
Tons
1, 1-1/2 or 2
2, 2-1/2 or 3
1, 1-1/2 or 2
2, 2-1/2 or 3
kW
3.5, 5.3 or 7.0
7.0, 8.8 or 10.6
3.5, 5.3 or7.0
7.0, 8.8 or 10.6
mm
Blower motor output hp (W)
Shipping weight lbs. (kg) 1 package
130 (59)
Electrical characteristics
135 (61)
120 volts 60 hertz 1 phase (less than 12 amps) All models
Optional Accessories (Must Be Ordered Extra) LPG/propane kit
LB-69845L (38K84)
Twinning Kit
15L3801 5 lbs. (2 kg)
Up Flow/Horizontal Filter and Filter Rack Kits
Up−Flow/Horizontal
N & sizeoffilters−
No.
i
f filt
in.
i (mm)
(
)
Down flow
Down-flow
Filt Kit
Filter
76.8%
4 (102)
High static certified by A.G.A./C.G.A. in wg. (Pa)
Nominal cooling
th t can b
that
be added
dd d
80.0%
3 (76)
Temperature rise range F (C)
Blower wheel nominal
di
diameter
t x width
idth
80.1%
Single (32J02) Ten Pack (66K64)
(1) 16 x 20 x 1 (406 x 508 x 25)
Catalog No.
LB-69843A (32J01) 3 lbs. (1 kg)
No. & Size of Filters in. (mm)
(2) 16 x 20 x 1 (406 x 508 x 25)
Down-flow Combustible Floor Base
LB-79239A (67J91) 10 lbs. (4 kg)
Sidewall Power Venting Kit
79J15 25 lbs. (11 kg)
Hanging Bracket Kit
Annual Fuel Utilization Efficiency based on U.S.
furnaces.
Polyurethane frame type filter is furnished with kit.
Filters are not furnished with kit and must be ordered extra.
LB-69957 (46J66) 15 lbs. (8 kg)
DOE
test
procedures
and
according
to
Page 2
FTC
labeling
regulations.
Isolated
combustion
system
rating
for
non-weatherized
SPECIFICATIONS continued
Model No.
80MGF4(X)-75
80MGF3/4(X)-100
80MGF4/5(X)-100
Input Btuh (kW)
75,000 (22.0)
100,000 (29.3)
Output Btuh (kW)
61,700 (18.1)
82,000 (24.0)
A.F.U.E.
80.0%
80.1%
80.0%
California Seasonal Efficiency
76.3%
76.5%
77.0%
Flue size connection diameter in. (mm) round
4 (102)
Temperature rise range F (C)
45 - 75 (25 - 42)
35 - 65 (19 - 36)
.50 (125)
.65 (162)
High static certified by A.G.A./C.G.A. in wg. (Pa)
Gas Piping Size I.P.S. Natural or LPG/propane
Blower wheel nominal
di
diameter
t x width
idth
1/2 (13)
in.
12 x 8
12 x 9
305 x 203
305 x 229
1/2 (373)
3/4 (560)
Tons
2, 2-1/2, 3, 3-1/2 or 4
3-1/2, 4, 5 or 6
kW
7.0, 8.8, 10.6, 12.3 or 14.1
12.3, 14.1, 17.6 or 21.1
mm
Blower motor output hp (W)
Nominal cooling
th t can b
that
be added
dd d
Shipping weight lbs. (kg) 1 package
140 (64)
Electrical characteristics
175 (79)
120 volts 60 hertz 1 phase (less than 12 amps) All models
Optional Accessories (Must Be Ordered Extra) LPG/propane kit
LB-69845L (38K84)
LB-69845K (81J14)
Twinning Kit
15L3801 5 lbs. (2 kg)
Up Flow/Horizontal Filter and Filter Rack Kits
Up−Flow/Horizontal
No. & sizeoffilters− in. (mm)
Down flow
Down-flow
Filter Kit
Single (32J02) Ten Pack (66K64)
(1) 16 x 20 x 1 (406 x 508 x 25)
Catalog No.
LB-69843A (32J01) 3 lbs. (1 kg)
No. & Size of Filters in. (mm)
Down-flow Combustible floor Base
(2) 16 x 20 x 1 (406 x 508 x 25)
LB-79239A (67J91) 10 lbs. (4 kg)
Sidewall Power Venting Kit
LB-79239B (67J92) 10 lbs. (4 kg)
79J15 25 lbs. (11 kg)
Hanging Bracket Kit
Annual Fuel Utilization Efficiency based on U.S.
furnaces.
Polyurethane frame type filter is furnished with kit.
Filters are not furnished with kit and must be ordered extra.
Single (46J14) Ten Pack (66K65)
(1) 20 x 20 x 1 (508 x 508 x 25)
LB-69957 (46J66) 15 lbs. (8 kg)
DOE
test
procedures
and
according
to
Page 3
FTC
labeling
regulations.
Isolated
combustion
system
rating
for
non-weatherized
SPECIFICATIONS continued
Model No.
80MGF3/4-120
80MGF4/5-140
80MGF4/5(X)-120
Input Btuh (kW)
120,000 (35.2)
140,000 (41.0)
Output Btuh (kW)
98,400 (28.8)
114,800 (33.6)
A.F.U.E.
California Seasonal Efficiency
80.0%
80.1%
80.0%
Not Available
75.5%
Not Available
Flue size connection diameter in. (mm) round
Temperature rise range F (C)
45 - 75 (25 - 42)
High static certified by A.G.A./C.G.A. in wg. (Pa)
.50 (125)
Gas Piping Size I.P.S. Natural or LPG/propane in. (mm)
Blower wheel nominal
diameter x width
in.
1/2 (13)
12 x 9
305 x 203
305 x 229
1/2 (373)
3/4 (560)
Tons
2, 2-1/2, 3, 3-1/2 or 4
3-1/2, 4, 5 or 6
kW
7.0, 8.8, 10.6, 12.3 or 14.1
12.3, 14.1, 17.6 or 21.1
mm
Shipping weight lbs. (kg) 1 package
190 (86)
175 (79)
Electrical characteristics
120 volts 60 hertz 1 phase (less than 12 amps) All models
Optional Accessories (Must Be Ordered Extra) LPG/propane kit
LB-69845K (81J14)
Twinning Kit
15L3801 5 lbs. (2 kg)
Up−Flow/Horizontal Filter and Filter Rack Kits
No. & sizeoffilters− in. (mm
Single (46J14) Ten Pack (66K65)
(1) 20 x 20 x 1 (508 x 508 x 25)
Catalog No.
Down-flow
Filter Rack
.65 (162)
12 x 8
Blower motor output hp (W)
Nominal cooling
that can be added
5 (127)
4 (102)
No. & Size
of Filters
Down-flow Combustible Floor Base
Single (58J93) Ten Pack (66K66)
(1) 20 x 20 x 1 (508 x 508 x 25)
LB-69843A (32J01) 3 lbs. (1 kg)
in.
(2) 16 x 20 x 1
mm
(2) 406 x 508 x 25
LB-79239B (67J92) 10 lbs. (4 kg)
Sidewall Power Venting Kit
LB-79239C (67J93) 12 lbs. (5 kg)
79J15 25 lbs. (11 kg)
Hanging Bracket Kit
LB-69957 (46J66) 15 lbs. (8 kg)
Annual Fuel Utilization Efficiency based on U.S. DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherized
furnaces.
Polyurethane frame type filter is furnished with kit.
2 in. x 5 in. (51 mm x 127 mm) flue adaptor furnished with -140 input furnaces for connection to furnace induced draft blower.
Filters are not furnished with kit and must be ordered extra.
Page 4
BLOWER PERFORMANCE DATA
80MGF2-45, 80MGF2-60 AND 80MGF2-75 BLOWER PERFORMANCE
Air Volume at Various Blower Speeds
External Static
Pressure
High
Medium-High
Medium-Low
Low
in. w.g.
Pa
cfm
L/s
cfm
L/s
cfm
L/s
cfm
L/s
0
0
1270
600
980
460
770
365
570
270
.05
12
1245
590
975
460
770
365
565
265
.10
25
1220
575
975
460
770
365
565
265
.15
37
1195
565
965
455
765
360
560
265
.20
50
1170
550
960
455
760
360
560
265
.25
62
1140
540
950
450
760
360
555
260
.30
75
1110
525
940
445
760
360
550
260
.40
100
1060
500
910
430
750
355
545
255
.50
125
990
465
880
415
740
350
540
255
.60
150
900
425
810
380
690
325
530
250
.70
175
800
380
740
350
630
295
520
245
NOTE All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished) in place. Also see Filter Air Resistance table
80MGF3-60 AND 80MGF3-75 BLOWER PERFORMANCE
Air Volume at Various Blower Speeds
External Static
Pressure
High
Medium-High
Medium-Low
Low
in. w.g.
Pa
cfm
L/s
cfm
L/s
cfm
L/s
cfm
L/s
0
0
1425
670
1240
585
1000
470
800
380
.05
12
1415
670
1230
580
995
470
800
380
.10
25
1400
660
1220
575
990
465
795
375
.15
37
1385
655
1200
565
985
465
795
375
.20
50
1370
645
1180
555
980
460
790
375
.25
62
1350
635
1160
545
970
460
780
370
.30
75
1330
630
1140
540
955
450
770
365
.40
100
1280
605
1095
515
925
435
750
355
.50
125
1210
570
1040
490
900
425
720
340
.60
150
1135
535
985
465
860
405
680
320
.70
175
1070
505
920
435
800
380
630
300
NOTE All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished) in place. Also see Filter Air Resistance table
Page 5
80MGF4-75, 80MGF3/4-100 AND 80MGF3/4-120 BLOWER PERFORMANCE
Air Volume at Various Blower Speeds
External Static
Pressure
High
Medium-High
Medium
Medium-Low
Low
in. w.g.
Pa
cfm
L/s
cfm
L/s
cfm
L/s
cfm
L/s
cfm
L/s
0
0
1830
865
1600
755
1325
625
1070
505
880
415
.05
12
1815
855
1585
750
1320
625
1070
505
880
415
.10
25
1800
850
1570
740
1315
620
1070
505
880
415
.15
37
1875
885
1550
730
1310
620
1065
505
875
415
.20
50
1750
825
1530
720
1300
615
1060
500
875
415
.25
62
1725
815
1515
715
1290
610
1050
495
870
410
.30
75
1700
800
1500
710
1275
600
1040
490
870
410
.40
100
1650
780
1460
690
1245
590
1020
480
860
405
.50
125
1600
755
1420
670
1210
570
1000
470
840
395
.60
150
1550
730
1380
650
1170
550
980
460
820
385
.70
175
1480
700
1330
630
1130
535
960
455
790
375
NOTE All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished) in place. Also see Filter Air Resistance table
80MGF4/5-100, 80MGF4/5-120 AND 80MGF4/5-140 BLOWER PERFORMANCE
Air Volume at Various Blower Speeds
External Static
Pressure
High
Medium-High
Medium
Medium-Low
Low
in. w.g.
Pa
cfm
L/s
cfm
L/s
cfm
L/s
cfm
L/s
cfm
L/s
0
0
2450
1155
2160
1020
1970
930
1700
800
1500
710
.05
12
2440
1150
2155
1015
1965
925
1695
800
1500
710
.10
25
2430
1145
2150
1015
1960
925
1690
800
1495
705
.15
37
2415
1140
2135
1010
1950
920
1685
795
1495
705
.20
50
2400
1135
2120
1000
1940
915
1680
795
1490
705
.25
62
2380
1125
2105
995
1930
910
1675
790
1480
700
.30
75
2360
1115
2090
985
1915
905
1670
790
1470
695
.40
100
2310
1090
2050
965
1870
880
1650
780
1440
680
.50
125
2260
1065
2000
945
1810
855
1610
760
1410
665
.60
150
2180
1030
1950
920
1750
825
1560
735
1370
645
.70
175
2100
990
1890
890
1700
800
1520
715
1330
630
NOTE All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished) in place. Also see Filter Air Resistance table
FILTER AIR RESISTANCE
cfm (L/s)
in. w.g. (Pa)
0 (0)
0.00 (0)
200 (95)
0.01 (2)
400 (185)
0.03 (7)
600 (280)
0.04 (10)
800 (375)
0.06 (15)
1000 (470)
0.09 (22)
1200 (560)
0.12 (30)
1400 (655)
0.15 (37)
1600 (750)
0.19 (47)
1800 (845)
0.23 (57)
2000 (935)
0.27 (67)
2200 (1030)
0.33 (82)
2400 (1125)
0.38 (95)
2600 (1220)
0.44 (110)
Page 6
80MGF PARTS IDENTIFICATION
and ORIENTATION
VENT ADAPTER
CABINET TOP
HEAT EXCHANGER
ASSEMBLY
FLUE BOX
COMBUSTION AIR
BLOWER
PRESSURE
SWITCH
80MGF
CABINET
PRIMARY
LIMIT
FRONT ACCESS
PANEL
NOx
TURBULATOR
BURNER
ASSEMBLY
TRANSFORMER
CONTROL
BOARD
SECONDARY
LIMITS
CABINET
BOTTOM
BLOWER ASSEMBLY
DOOR INTERLOCK SWITCH
FIGURE 1
HEATING COMPONENTS (shown in horizontal position)
PRIMARY LIMIT
ROLLOUT SWITCH (2)
COMBUSTION AIR
PROVE SWITCH
MANIFOLD
Left
Bottom
BURNERS
Back
Front
Top
Right
HEAT EXCHANGER
GAS VALVE
COMBUSTION AIR BLOWER
COLLECTOR
FIGURE 2
Page 7
80MGF BURNER ASSEMBLY
(Shown With SureLight ignitor)
SURELIGHT
IGNITOR
ROLLOUT
SWITCHES
BURNER BOX
TOP
VEST PANEL
UPPER
BURNER
MOUNTING
RAIL
LOWER
BURNER
MOUNTING
RAIL
FLAME
SENSOR
BURNER
HEAT EXCHANGER
PRIMARY LIMIT
Top
Back
ORIFICE
Left
GAS VALVE
Right
Front
BURNER BOX
MANIFOLD
Bottom
FIGURE 3
80MGF BLOWER DOOR COMPONENTS − BLOWER ACCESS
(SureLight MODEL SHOWN)
To Access Blower:
1− Turn off power to unit and disconnect L1 and L2
line voltage power.
2− Disconnect thermostat wiring connections
from furnace control board.
3− Disconnect blower leads from control board.
4− Disconnect J1 from P1.
5− Disconnect 6 pin P156 from control board.
6− Disconnect 9 pin P58 from control board.
7− Disconnect sensor wiire from center of board.
8− Remove screws (2) and lift panel from unit.
4
7
5
Top
3
Right
6
8
2
1
FIGURE 4
Page 8
Back
Left
Front
Bottom
I−UNIT COMPONENTS (Figures 1, 2, 3)
80MGF unit components are shown in figure 1. The blower
controls, gas valve and burners can be accessed by removing the front access panel. A separate blower access
door is located behind the front access panel. Electrical
control components are mounted to the blower access
door.
80MGF units are factory equipped with bottom return air panels. The panels are designed to be field removed as required
for bottom air return. Indentations on side of units, show
where side air return opening should be cut during installation.
A−Blower Door Components (Figure 4)
Electrical burner control and blower control components
are located on the outside surface of the blower access
door. Jackplugs allow the blower door to be easily removed for blower service.
Located on the blower door are the unit transformer (T1),
the furnace control (A3) and door interlock switch (S51).
Furnace control (A3) combines the function of a burner
ignition control and blower control.
1− Control Transformer (T1)
A transformer located on the blower door provides power
to the low voltage section of the unit. Transformers on all
models are rated 30VA with a 120V primary and a 24V secondary.
2−Door Interlock Switch (S51)
A door interlock switch rated 16A at 125VAC is located on
the blower access door. The switch is wired in series with
line voltage. When the blower door is removed the unit will
shut down.
3− Ram Control (A3)
The furnace control combines burner ignition functions
with blower control functions.
Some early model 80MGF units utilize a furnace control
manufactured by RAM Electronics Corporation. The RAM"
board is a printed circuit board which controls the blower, gas
valve, combustion air blower and ignition spark. It also monitors the flame, limit and gas valve operation. The control has
a non−adjustable, factory preset on" fan timing (45 seconds). Fan off" timings are adjustable. The board utilizes
both 120 and 24VAC. See figure 5. The board is also
equipped with a diagnostic LED for use when troubleshooting the unit.
When the furnace is idle (blower off and no heating or cooling demand), the diagnostic LED flashes at a slow steady
rate. On a call for heat, the diagnostic LED begins flashing
at a fast rate and the combustion air blower is energized.
The LED flashes different codes to indicate problem con-
ditions. The diagnostic LED lights red (not flashing) to indicate control board failure. Table 3 shows how to interpret the
other LED modes.
Pre-Purge
On a call for heat, the combustion air blower begins operating. If the combustion air prove switch closes, the combustion air blower continues to operate for 45 seconds
(pre-purge) before allowing ignition. Pre-purge allows the
heat exchanger to be cleared of combustion products and
to introduce fresh air for combustion. If the combustion air
prove switch does not close, the combustion air blower
continues to run indefinitely (until the prove switch closes).
Post-Purge
After a demand, the combustion air blower continues to
operate for 5 seconds (post-purge) before stopping. Postpurge allows the heat exchanger to be cleared of combustion products.
Ignition Control
The ignition control is a direct spark ignition control module
integral to the furnace control. See figure 5. When there is a
call for heat, the control delays ignition until combustion air
blower operation has been proved and pre-purge period
has elapsed. It then opens the gas valve and generates a
spark to ignite the burners. Trial for ignition lasts for 7 seconds. At the same time, the control begins monitoring the
flame sensor. If the flame current is too weak (less than 1
microamp) or if the burners do not ignite (within the 7 second ignition trial), the control will shut off spark and the combustion air blower and de-energize the gas valve. Flame
current should be between 1 and 5 microamps to keep the
gas valve open. See figure 23.
The control will attempt to ignite the burners up to two more
times. Each time the control restarts the ignition sequence,
it begins with a 45 second pre-purge. If flame is not sensed
after the third trial, the control locks out. Lockout means that
the control shuts off the gas valve, spark and combustion air
blower for 60 minutes. At the end of 60 minutes the control
completely resets and will attempt ignition up to three times.
The control can be manually reset before the end of 60 minutes by momentarily turning off power to the unit.
Page 9
DANGER
Shock hazard.
Spark related components contain high voltage.
Disconnect power before servicing. Control is
not field repairable. If control is inoperable, simply replace entire control.
Can cause injury or death. Unsafe operation will
result if repair is attempted.
RAM CONTROL (A3)
SPARK OUTPUT
24VAC VOLT
TERMINAL
CONNECTIONS
LINE VOLTAGE
TERMINAL
CONNECTIONS
See Table 2 for
Terminal Functions
See Table 2 for
Terminal Functions
FAN-OFF TIMING
SWITCHES
THERMOSTAT
CONNECTIONS
DIAGNOSTIC
LED
FIGURE 5
TABLE 1
Furnace Control A3 Limit Response During Operation
Response
Condition
Loss of Flame
Sensed Before
End of 45 second Blower On
Delay
(3 or Fewer
Trials
for Ignition)
Combustion
Air
Blower
Gas
Valve
Supply
Air
Blower
Diagnostic
LED
On
On
(Spark
Starts
Within 0.8
seconds)
On
Fast Flash
Blower Control and Timings
DANGER
Loss of Flame
Sensed After
45 second
Blower On
Delay (3 or
Fewer Trials
for Ignition)
On
Loss of Flame
Sensed (More
Than 3 Trials
for Ignition)
Off
Off
Off
2 Flashes
Flame Sensed
Without
Demand
On
Off
On
5 Flashes
Primary or Secondary Limit
Open
On
Off
On
4 Flashes
Rollout Switch
Open
On
Off
On
4 Flashes
Combustion Air
Prove Switch
Open
On
Off
On
3 Flashes
Off Then
On With
Spark
After PrePurge
When flame is sensed, the indoor blower starts after a 45
second delay. Gas valve remains open and blower continues to run until demand stops, flame sensor senses loss of
flame, a limit opens or the prove switch opens. If any of
these events occur during a thermostat demand, the gas
valve closes and the diagnostic LED registers the error
condition (table 1).
On
Electrical Shock Hazard.
This control contains field adjustable switches
and also contains line voltage. Make sure power
is disconnected before making any field adjustments or performing any service procedure.
Fast Flash
NOTEIf fan off" time is set too low, residual heat in
heat exchanger may cause primary limit S10 to trip resulting in frequent cycling of blower. If this occurs, adjust blower to longer time setting.
Fan ON" timing (time that the burners operate before the
supply air blower starts) is fixed at 45 seconds and cannot
be adjusted.
Page 10
Fan OFF" timings (time that the blower operates after a
heating or cooling demand has been satisfied) are determined by the arrangement of switches on the furnace
control board. See figure 5. To adjust fan off " timings,
gently reposition the switches to a new timing position.
Figure 6 shows the various fan off" timings and how
switches should be positioned. 80MGF−1, −2, −3, −4 and −6
units are shipped with a factory fan off" setting of 180 seconds. 80MGF−5 and −7 units are shipped with factory "off"
setting of 60 seconds. Fan off" time will affect comfort and
efficiency and is adjustable to satisfy individual applications. The fan off" timing is initiated after a heating or cooling demand but not after a blower demand (that is, when
indoor thermostat switch is changed from ON to AUTO
and heating/cooling demand is not present, the blower
stops immediately).
TABLE 2
C
Screw Strip
Screw Strip
Screw Strip
Screw Strip
Early Units
1/4" Spade
Later Units
Screw Strip
LOCATED ON FURNACE CONTROL (A3)
Fan-Off Timings
Switch
1
2
Timing
Seconds
Off
Off
On
Off
On
Off
90
120
180
On
On
240
FIGURE 6
Diagnostic LED
The furnace control is equipped with a diagnostic LED
used for troubleshooting the unit and the control. LED
functions are shown in table 3.
TABLE 3
Furnace Control A3 Diagnostic LED
Meaning
Remedy
Steady On
Control Failure
Replace Control
Slow Flash
Normal Operation and
No Call For Heat
----
Fast Flash
Normal Operation with
Call For Heat
----
24VAC Common
Two
Flashes
Control Lockout
Failed to Sense or Sustain
Flame. Check Gas Valve,
Burners, Spark Electrode
and Wire, Flame Sensor.
Replace Control If All OK.
Three
Flashes
Pressure Switch Open
Failed to Prove Combustion Blower Operation or
Blocked Vent. Repair or
Replace as Necessary.
Four
Flashes
Open Limit
Check Primary Limit, Rollout
Switches and Secondary
Limits. Find source of Overtemperature. If all OK, Reset
or Replace Limits as Necessary.
Five
Flashes
Flame Sensed and Gas
Valve Not Energized.
Check Gas Valve. If OK,
Check Flame Sensor.
FURNACE CONTROL A3 TERMINAL DESIGNATIONS
Terminal
Type
Function
Y
G
R
W
FAN-OFF TIME ADJUSTMENT SWITCHES
Cooling Demand
Blower Demand
24VAC to Thermostat
Heating Demand
120VAC HOT
AUX
1/4" Spade
1/4" Spade
CMB BLWR
1/4" Spade
Line Voltage In
Line Voltage Out (Switched)
Switched 120VAC to
Combustion Air Blower
ACB HEAT
1/4" Spade
Switched 120VAC to
Blower Heating Tap
ACB COOL
1/4" Spade
Switched 120VAC to Blower
Cooling Tap
VALVE
24VAC HOT
GROUND
FLAME SENSE
1/4" Spade
1/4" Spade
1/4" Spade
1/4" Spade
PSW
1/4" Spade
HI LIMIT IN
1/4" Spade
HI LIMIT OUT
1/4" Spade
24VAC to Gas Valve
24VAC In From Transformer
To Cabinet Ground
Flame Microamp Sensing
24VAC In From Pressure Switch
Switch Open: Prohibits Ignition
Switch Closed: Allows Ignition
24VAC In From Limits
Limit Open: Closes Gas Valve
Limits Closed: Allows Ignition
24VAC to Limit Train
and Pressure Switch
ROLLOUT IN
1/4" Spade
24VAC In From Rollout Switches
LED State
Page 11
4− EGC Control (A3)
Some early model 80MGF units are equipped with an integrated ignition/blower control (EGC−1 or EGC−2) which controls ignition, safety circuits, blower operation, fan off timing,
and allows for thermostat connection and troubleshooting. The EGC is a printed circuit board which is divided
into two sections, 120 and 24VAC. Line voltage comes
into the board on the 120VAC side. See figure 8. Terminal
designations are listed in tables 5 and 6.
Ignition Control
80MGF units use the EGC direct spark integrated ignition control. The EGC controls and monitors the entire
sequence of operation. On a call for heat from the thermostat the control monitors the combustion air blower
pressure switch. The control will not begin the heating
cycle if the pressure switch is closed (by-passed). Once
the pressure switch is determined to be open, the combustion air blower is energized. When the differential in pressure across the pressure switch is great enough, the pressure switch closes and a 15 second pre-purge period
begins. After the pre-purge period, the gas valve will open
and ignition (spark) will be attempted for 10 seconds. After
ignition, the control initiates a ten second flame stabilization period. The flame stabilization period allows the
burners to heat up and the flame to stabilize. Once flame
is established, the control will constantly monitor the burner
flame using flame rectification. Flame failure response time is
0.8 seconds.
If the initial attempt for ignition fails, the sequence is repeated up to five times. After the fifth trial, the control goes into
Watchguard"*. During watchguard mode, the entire unit will
be de-energized for one hour. After one hour the control will
repeat the ignition sequence. Watchguard may be manually
reset by breaking and remaking thermostat demand.
when no voltage should be present, the control de-energizes
the combustion air blower which terminates voltage to the
valve. The system goes into hard lock-out which is reset only
by removing power to the unit.
If flame is sensed when no flame should be present, the control will energize the combustion and indoor blowers. The
unit will remain locked in this sequence until the flame is no
longer sensed or the main power is turned off to reset the
control.
DANGER
Shock hazard. Avoid personal injury. Make sure to
disconnect power before changing fan off" timing.
Blower Operation / Fan Off Timings
Fan off" timing (time that the blower operates after the heat
demand has been satisfied) can be adjusted by moving the
jumper on the EGC blower control board. Figure 7 shows
the various fan off" timings and how jumper should be positioned. To adjust fan off " timing, gently disconnect jumper
and reposition across pins corresponding with new timing.
Unit is shipped with a factory fan off" setting of 180 seconds.
Fan on" time is factory set at 45 seconds following the
opening of the main gas valve and is not adjustable.
Fan off" time will affect comfort and efficiency and is adjustable to satisfy individual applications. The fan off" timing is initiated after a heating demand but not after a cooling demand.
NOTEIf fan off" time is set too low, residual heat in
heat exchanger may cause primary limit S10 to trip, resulting in frequent cycling of blower. If this occurs, adjust
blower to longer fan off" time setting.
*NOTE−If flame is established beyond the 10 second flame
stabilization period then lost, the control resets for five more
ignition trials. The control can be reset five times during one
unsatisfied thermostat demand, providing a maximum
of 25 trials for ignition.
Safety Circuits
During the entire heating demand the control monitors the
safety circuits. If the primary or secondary heating limits
open, the control de-energizes the main gas valve and
combustion air blower while the indoor blower remains energized. When the limit automatically resets, the ignition sequence also resets. If either of the limits trip five consecutive times during one unsatisfied thermostat demand, the
control will go into watchguard for one hour.
The control monitors main valve voltage. If voltage is sensed
FAN-OFF TIME ADJUSTMENT
TIMING
JUMPER
180
To adjust fan-off timing:
Remove jumper from EGC and select one
of the other pin combinations to achieve
the desired time.
60
TIMING PINS
(seconds)
Leave jumper off for
240 second fan-off timing.
120
90
FIGURE 7
Thermostat Connection
Thermostat wires are connected to the terminal strip
found on the EGC control board.
Page 12
Troubleshooting
TABLE 4
The EGC control board is equipped with two diagnostic green
LEDs to indicate the mode of failure. The LED lights are
marked DIAG #1 and DIAG #2. The codes are given in table
4. On the EGC−1 only, the last failure code is stored in
memory and may be retrieved by depressing and holding
the memory recall button. When this button is depressed,
the LEDs will signal the last failure code in memory. Power
must be restored to the control (depress blower interlock
switch) within one minute of blower access panel removal in
order to retain memory. To clear the memory of the stored
failure code, remove main power and short the jumper next
to the diagnostic button for five seconds.
EGC DIAGNOSTIC CODES
DIAG #1
DIagnostic Condition
DIAG #2
Simultaneous
Flash
Simultaneous
Flash
On
Flash
Flash
Off
Alternate
Flash
Alternate Flash
Off
Flash
Flash
On
Continuous
On
Continuous On
EGC−2 INTEGRATED CONTROL
8
*
* *
9
10 11 12
13
14
*
* *
15
16
Power ON". Normal Operation. Increased flash rate indicates there
is a heating demand.
Primary or Secondary
Limit Switch Open.
Auto-Reset Switch.
Pressure Switch Watchguard,
pressure switch opened during
operation or condensate
drain blocked.
Watchguard, burners
failed to ignite.
Flame sensed without
valve energized.
Roll-out Switch Open.
Manual-Reset Switch.
Circuit board self-check failure or
ignition/blower control
is wired incorrectly.
NOTE: EGC−1 board will have terminal (#15) for
7
ACB low speed.
NOTE: EGC−1 board will have terminal
(#16) for ACB Heat speed.
6
5
4
DIAGNOSTIC LEDS
DIAGNOSTIC MODULE
BLOWER TIME
ADJUSTMENT
JUMPER
THERMOSTAT
TERMINAL STRIP
(DETACHABLE)
1
EDGE
CONNECTION
2
7
8
5
3
24VAC
PLUG P20
4
6
9
3 2
1
RED DIAGNOSTIC BUTTON
DIAGNOSTIC CODE ERASE JUMPER
(EGC−1 only. Depress button and hold (Remove power to control and short pins for
for display of last failure code.)
10 seconds to erase previous code.)
FIGURE 8
Page 13
TABLE 5
BLOWER CONTROL A15 TERMINAL DESIGNATIONS
Terminal
Designation
Type
Function
(See fig. 8)
R
Screw Strip
G
Screw Strip
W
Screw Strip
Y
Screw Strip
C
1
2
3
4, 5, 6
Screw Strip
1/4" Spade
1/4" Spade
1/4" Spade
1/4" Spade
7
1/4" Spade
8
9
10
11
12, 13
14
1/4" Spade
1/4" Spade
1/4" Spade
1/4" Spade
1/4" Spade
1/4" Spade
15
1/4" Spade
16
1/4" Spade
24VAC to Thermostat (Red)
Manual Fan Input from Thermostat
(Green)
Heat Demand Input from Thermostat
(White)
Cool Demand Input from Thermostat
(Yellow)
Common Ground to Thermostat
24VAC Hot from Transformer
24VAC Return to Transformer
24VAC Ground
120VAC Return − 120VAC Common
120VAC Return − 120VAC Common
Input
Combustion Blower (Line Voltage)
Heat Only Accessory (Line Voltage)
120VAC Hot to Transformer
120VAC Hot Input
Accessories (Line Voltage)
ACB Cool Speed (Line Voltage)
EGC−1 ACB Low Cont. Speed
(Line Voltage)
EGC−2 ACB Heat Speed
(Line Voltage)
ACB Heat Speed (Line Voltage)
5−Flame Sensor (−11 models)
A flame sensor is located on the left side of the burner support. See figure 9. The sensor is mounted on a bracket in
the burner support and the tip protrudes into the flame envelope of the left−most burner. The sensor is fastened to
burner supports and can be removed for service without
removing any part of the burners. During operation, flame
is sensed by current passed through the flame and sensing electrode. The SureLight control allows the gas valve
to remain open as long as flame signal is sensed.
NORMAL FLAME SIGNAL u 0.7 MICROAMPS
LOW FLAME SIGNAL
v 0.7 MICROAMPS
MINIMUM FLAME SIGNAL v 0.15 MICROAMPS
1/4 in. 7 mm
1/32 in. 0.79
mm
BURNER
FLAME
TABLE 6
Rollout Switch Out
Spare
Gas Valve Common
Pressure Switch Return
Hi Limit Return / Pressure Switch Out
Flame Sensor
Gas Valve Out
High Limit Out
Rollout Switch Return
DANGER
Shock hazard.
Disconnect power before servicing. Control is not
field repairable. If control is inoperable, simply
replace entire control.
Can cause injury or death. Unsafe operation will
result if repair is attempted.
3/16 in.
4.7 mm
SIDE VIEWSENSOR
END VIEW
FIGURE 9
NOTE − The 80MGF furnace contains electronic components that are polarity sensitive. Make sure that the
furnace is wired correctly and is properly grounded.
EGC CONTROL JACK/PLUG 20 TERMINAL DESIGNATIONS
Pin #
Function
1
2
3
4
5
6
7
8
9
11/16 in. 18 mm
1/32 in. 0.79
mm
6− SureLight Ignition System A3
(−11 models)
All 80MGF−11 model units are equipped with the Lennox
SureLight ignition system. The system consists of ignition
control board (figure 11 with control terminal designations in table 10) and ignitor (figure 12). The board and ignitor work in combination to ensure furnace ignition and
ignitor durability. The SureLight integrated board controls
all major furnace operations. The board also features two
LED lights for troubleshooting and two accessory terminals rated at (4) four amps. See table 9 for troubleshooting diagnostic codes. Table 7 and 8 show jack plug terminal designations. Units equipped with the SureLight
board can be used with either electronic or electro−mechanical thermostats without modification. The SureLight
ignitor is made of durable silicon−nitride. Ignitor longevity
is also enhanced by voltage ramping by the control board.
The board finds the lowest ignitor temperature which will
successfully light the burner, thus increasing the life of the
ignitor.
Page 14
TABLE 7
SureLight BOARD J156 (J2) TERMINAL
DESIGNATIONS
PIN #
FUNCTION
1
Ignitor
2
Not Used
3
Ignitor Neutral
4
Combustion Air Blower Line Voltage
5
Not Used
6
Combustion Air Blower Neutral
TABLE 8
SureLight BOARD J58 (J1) TERMINAL
DESIGNATIONS
PIN #
FUNCTION
1
Primary Limit In
2
Gas Valve Common
3
Roll Out Switch Out
4
Gas Valve 24V
5
Pressure Switch In
6
Pressure Switch and Primary Limit Out
7
Not Used
8
Roll Out Switch In
9
Ground
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
CAUTION
Electrostatic discharge can affect electronic
components. Take precautions during furnace
installation and service to protect the furnace’s
electronic controls. Precautions will help to avoid
control exposure to electrostatic discharge by
putting the furnace, the control and the technician at the same electrostatic potential. Neutralize electrostatic charge by touching hand and all
tools on an unpainted unit surface, such as the
gas valve or blower deck, before performing any
service procedure.
a−Electronic Ignition
On a call for heat the SureLight control monitors the combustion air blower pressure switch. The control will not begin the heating cycle if the pressure switch is closed (by−
passed). Once the pressure switch is determined to be
open, the combustion air blower is energized. When the
differential in the pressure switch is great enough, the
pressure switch closes and a 15−second pre−purge begins. If the pressure switch is not proven within 2−1/2 minutes, the control goes into Watchguard−Pressure Switch
mode for a 5−minute re−set period.
After the 15−second pre−purge period, the SureLight ignitor warms up for 20 seconds after which the gas valve
opens for a 4−second trial for ignition. 80MGF units with
board 63K89, 24L85 or 56L83: the ignitor stays energized
for the first second of the 4−second trial. Units with board
97L48: ignitor stays energized for the full 4−second trial for
ignition. If ignition is not proved during the 4−second period, the control will try four more times with an inter purge
and warm−up time between trials of 35 seconds. After a total of five trials for ignition (including the initial trial), the
control goes into Watchguard−Flame Failure mode. After a
60−minute reset period, the control will begin the ignition
sequence again.
The SureLight control board has an added feature that
prolongs the life of the ignitor. After a successful ignition,
the SureLight control utilizes less power to energize the ignitor on successive calls for heat. The control continues to
ramp down the voltage to the ignitor until it finds the lowest
amount of power that will provide a successful ignition.
This amount of power is used for 255 cycles. On the 256th
call for heat, the control will again ramp down until the lowest power is determined and the cycle begins again.
b−Fan Time Control
The fan on time of 45 seconds is not adjustable. Fan off
time (time that the blower operates after the heat demand
has been satisfied) can be adjusted by flipping the dip
switches located on the SureLight integrated control. The
unit is shipped with a factory fan off setting of 90 seconds.
Fan off time will affect comfort and is adjustable to satisfy
individual applications. See figure 10.
FAN-OFF TIME ADJUSTMENT
60sec.
90sec.
120sec.
180sec.
To adjust fan−off timing, flip dip switch to desired setting.
FIGURE 10
Page 15
The SureLight board is equipped with two LED lights for troubleshooting. The lights are found just above the 24VAC terminal strip see figure 8. The diagnostic codes are listed below in table 9.
TABLE 9
DIAGNOSTIC CODES
MAKE SURE TO ID LED’S CORRECTLY: REFER TO INSTALLATION INSTRUCTIONS FOR CONTROL BOARD LAYOUT.
LED #1
LED #2
DESCRIPTION
SIMULTANEOUS
SLOW FLASH
SIMULTANEOUS
SLOW FLASH
Power − Normal operation
Also signaled during cooling and continues fan.
SIMULTANEOUS FAST
FLASH
SIMULTANEOUS FAST
FLASH
Normal operation − signaled when heating demand initiated at thermostat.
SLOW FLASH
ON
OFF
SLOW FLASH
ALTERNATING SLOW
FLASH
ALTERNATING SLOW
FLASH
SLOW FLASH
OFF
ON
ON
ON
OFF
SLOW FLASH
ON
OFF
ON
FAST FLASH
SLOW FLASH
SLOW FLASH
FAST FLASH
ALTERNATING FAST
FLASH
ALTERNATING FAST
FLASH
Primary or Secondary limit open. Units with board 63K8901 or 24L85: Limit must
close within 5 trials for ignition or board goes into one hour limit Watchguard.
Units with board 56L83 or 97L48: Limit must close within 3 minutes or board
goes into one hour limit Watchguard.
Pressure switch open or has opened 5 times during a single call for heat; OR:
Blocked inlet/exhaust vent; OR: Condensate line blocked; OR: Pressure switch
closed prior to activation of combustion air blower.
Watchguard − burners fail to ignite.
Flame sensed without gas valve energized.
Rollout switch open. OR: 9 pin connector improperly attached.
Circuit board failure or control wired incorrectly.
Main power polarity reversed. Switch line and neutral.
Low flame signal. Measures below .7 microAmps. Replace flame sense rod.
Improper main ground or line voltage below 75 volts; OR: Broken ignitor; OR:
Open ignitor circuit.
NOTE − Slow flash equals 1 Hz (one flash per second). Fast flash equals 3 Hz (three flashes per second). Drop out flame sense current < 0.15 microAmps
SureLight Ignitor
SURELIGHT INTEGRATED CONTROL BOARD
SURELIGHT IGNITOR
FIGURE 12
TABLE 10
TERMINAL DESIGNATIONS
ACB COOL
Blower − Cooling Speed (Line Volt)
ACB HEAT
Blower − Heating Speed (Line Volt)
PARK
Alternate Blower Speeds (Dead)
Continuous Low Speed Blower
ACB LOW
Accessory Terminal (Line Volt)
ACC
TX
120VAC Hot to Transformer
HOT
120VAC Hot Input
HTG ACC
Heat Only Accessory (Line Volt)
120VAC Neutrals
NEUTRALS
24VAC Hot from Transformer
24VAC HOT
24VAC RTN
24VAC Return from Transformer
FLAME SENSE Flame Sense Terminal
FIGURE 11
Page 16
B−Blower Motors and Capacitors
All 80MGF units use direct drive blower motors. All motors
used are 120V permanent split capacitor motors to ensure
maximum efficiency. See table 11 for ratings.
TABLE 11
80MGF BLOWER RATINGS 120V 1PH
BLOWER MOTOR
80MGF2
80MGF3
80MGF3/4
80MGF4
80MGF4/5
80MGF5/6
HP
1/4
1/3
1/2
1/2
3/4
3/4
CAP
5MFD 370V
5MFD 370V
7.5MFD 370V
7.5MFD 370V
40MFD 370V
40MFD 370V
SUPPLY AIR BLOWER
AND SECONDARY LIMITSSECONDARY
LIMITS (S21)
Top
Back
Left
Front
Bottom
Right
tive. If pressure becomes less negative (signifying an obstruction) the pressure switch opens. When the pressure
switch opens, the furnace control (A3) immediately closes
the gas valve to prevent burner operation.
D−Flame Rollout Switches (S47)
Flame rollout switch is a high temperature limit located on
top of the burner box. Each furnace is equipped with two
identical switches. One switch is located over the leftmost
burner and the other switch is located over the rightmost
burner. The limit is a N.C. SPST manual-reset limit connected in series with the ignition control A3. When S47
senses rollout, the ignition control immediately stops ignition and closes the gas valve. If unit is running and flame
rollout is detected, the gas valve will close and ignition control will be disabled. Rollout can be caused by a blocked
flue or lack of combustion air. The switch is factory set and
cannot be adjusted. The setpoint will be printed on the side of
the limit. The switch can be manually reset. To manually reset a tripped switch, push the reset button located on the
control.
ROLLOUT SWITCH (S47)
MANUAL
RESET BUTTON
BLOWER
MOTOR
FIGURE 14
MOTOR
CAPACITOR
E−Primary Limit Control (S10)
To Remove Blower From Unit: Remove Bolts and
Wiring Jackplugs. Then Slide Out Front of Unit.
LIMIT CONTROL FOR
80MGF SERIES UNITS
FIGURE 13
THIS TYPE AUTO-RESET LIMIT
IS USED FOR THE PRIMARY LIMIT (S10) AND
RIGHT SECONDARY LIMIT (S21)
(see FIGURE 13)
C−Combustion Air Blower (B6)
All 80MGF units use a combustion air blower to move air
through the burners and heat exchanger during heating
operation. The blowers will use either a shaded pole 120V
motor or a C−frame 120V motor. Shaded pole and C−frame
motors do not use run capacitors. The motor operates during all heating operation and is controlled by furnace control A3. The motor also operates for a period before burner
ignition (pre−purge). The pre−purge time is 45 seconds for
80MGF units equipped with the RAM control and 15 seconds for units equipped with the EGC control. With either
the RAM, EGC or SureLight control board, the motor will
operate 5 seconds after the gas valve closes (post-purge).
A pressure switch connected to the combustion air blower
housing is used to prove combustion air blower operation.
The switch monitors air pressure in the blower housing. During normal operation, the pressure in the housing is nega-
FIGURE 15
The primary limit (S10) on 80MGF units is located in the
middle of the heating vestibule panel. When excess heat is
sensed in the heat exchanger, the limit will open. If the limit is
tripped, the furnace control energizes the supply air blower
and closes the gas valve. The limit automatically resets when
unit temperature returns to normal. The switch is factory set
and cannot be adjusted. The switch may have a different
setpoint for each unit model number. However, the setpoint
will be printed on the side of the limit. There are two types of
primary limit. See figures 15 and 16.
Page 17
F−Secondary Limit Controls (S21)
The secondary limit (S21) on 80MGF units is located in the
blower compartment in the back side of the blower housing.
When excess heat is sensed in the heat blower compartment,
the limit will open. If the limit is tripped, the furnace control energizes the supply air blower and closes the gas valve. The
limit automatically resets when unit temperature returns to
normal. The switch is factory set and cannot be adjusted.
Two limits are supplied in each furnace and each limit is a
different style (figures 15 and 16). The setpoint will be
printed on the side of the limit. If stick limit (Figure 16) suffers from nuisance trips and the furnace is in the horizontal
position, replace with limit kit no. 50L98.
LIMIT CONTROL (S21) (S10)
FOR 80MGF SERIES UNITS
G−Spark Electrode and Flame Sensor
(Models with EGC or Ram control only)
Figure 17 shows the arrangement of flame sensor, spark
electrode and burners. The Ram and EGC ignition control
uses direct spark to ignite the rightmost burner and the
burners cross-light to the left. The flame sensor uses flame
rectification to sense combustion. A flame retention ring in
the end of each burner is used to maintain correct flame
length and shape and to keep the flame from lifting off the
burner head.
Figure 18 shows the gap between tip of the electrodes and
the burner surface.
H−Gas Valve
THIS TYPE AUTO-RESET LIMIT IS
USED FOR THE LEFT SECONDARY
LIMIT (S21) (see FIGURE 13)
LIMIT
SPADE CONNECTORS
LIMIT
INSULATING COVER
The 80MGF uses a gas valve manufactured by Honeywell or WhiteRodgers. The valve is internally redundant to
assure safety shut−off. If the gas valve must be replaced,
the same type valve must be used.
24VAC terminals and gas control knob are located on top of
the valve. All terminals on the gas valve are connected to
wires from the electronic ignition control. 24V applied to the
terminals energizes the valve.
Inlet and outlet pressure taps are located on the valve. A regulator adjustment screw is located on the valve. Refer to figures
19 or 20 for location of valve features.
INSULATING COVER (s)
FIGURE 16
An LPG changeover kit is available from Lennox. The kit includes burner orifices and a regulator conversion kit.
TYPICAL BURNER/ELECTRODE ORIENTATION
DIRECT SPARK MODELS ONLY
1/8"(+1/64")
SPARK ELECTRODE
UPPER BURNER
MOUNTING RAIL
GROUND
BURNER
MANIFOLD
FLAME RETENTION RING
FIGURE 17
Page 18
LOWER BURNER
MOUNTING RAIL
23/32 in.
(18 mm)
Top
Right
ORIFICE
FLAME SENSOR
Left
Bottom
The switch is a single-pole single-throw pressure switch
electrically connected to the furnace control. The purpose
of the switch is to prevent burner operation if the combustion air blower is not operating.
SPARK ELECTRODE TO BURNER GAP
BURNER
5/16 in.
(7 mm)
PROVE SWITCH
COMBUSTION AIR BLOWER
PROVE SWITCH
Normally Open
Closes on Negative Pressure
SPARK
ELECTRODE
SPARK ELECTRODE
FLAME SENSOR TO BURNER GAP
BURNER
5/16 in.
(7 mm)
Sensing Tube
Attaches to Top
Side Of Blower
Back
PROVE
SWITCH
FLAME SENSOR
Left
FIGURE 18
Top
Right
Front
Bottom
WHITE RODGERS 36E SERIES GAS VALVE
FIGURE 21
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
On start-up, the switch senses that the combustion air
blower is operating. It closes a circuit to the furnace control
when pressure inside the combustion air blower increases
above pressure switch set point (In. negative w.c.). The
pressure sensed by the switch is relative to atmospheric
pressure. If the flue becomes obstructed during operation,
the switch senses a loss of negative pressure (pressure
becomes more equal with atmospheric pressure) and
opens the circuit to the furnace control and gas valve. The
switch trip pressure is different depending on unit model
number. The trip pressure is printed on the side of the limit.
The switch is factory set and is not field adjustable. It is a
safety shut-down control in the furnace and must not be
bypassed for any reason.
MANIFOLD
PRESSURE
OUTLET
GAS VALVE SHOWN IN OFF POSITION
FIGURE 19
HONEYWELL VR8205 SERIES GAS VALVE
MANIFOLD
PRESSURE
OUTLET
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
II−PLACEMENT AND INSTALLATION
Make sure unit is installed in accordance with installation
instructions and applicable does.
ON
III−START-UP
OFF
GAS VALVE SHOWN IN OFF POSITION
FIGURE 20
I−Combustion Air Blower Prove
(Pressure) Switch (S64)
80MGF series units are equipped with a combustion air
prove switch located on the vestibule panel. The switch is
connected to the combustion air blower housing by means
of a flexible silicone hose. It monitors air pressure in the
combustion air blower housing.
BEFORE LIGHTING smell all around the appliance area
for gas. Be sure to smell next to the floor because some gas
is heavier than air and will settle on the floor.
Use only your hand to turn the gas control knob. Never use
tools. If the knob will not turn by hand, do not try to repair it,
call a qualified service technician. Force or attempted repair
may result in a fire or explosion.
Page 19
A−Preliminary and Seasonal Checks
C−Safety or Emergency Shutdown
1− Inspect electrical wiring, both field and factory installed
for loose connections. Tighten as required.
2− Check voltage at disconnect switch. Voltage must be
within range listed on the nameplate. If not, consult the
power company and have voltage condition corrected
before starting unit.
B−Heating Start-Up
1 − STOP! Read the safety information at the beginning
of this section.
2 − Set thermostat to lowest setting.
3 − Turn off all electrical power to appliance.
4 − This appliance is equipped with an ignition device
which automatically lights the burners. Do not try to
light the burners by hand.
5 − Remove access panel.
Turn off unit power. Close manual and main gas valves.
D−Extended Period Shutdown
Turn off thermostat or set to UNOCCUPIED" mode. Close
all gas valves (both internal and external to unit) to guarantee no gas leak into combustion chamber. Turn off power
to unit. All access panels, covers and vent caps must be in
place and secured.
IV−HEATING SYSTEM SERVICE CHECKS
A−A.G.A./C.G.A. Certification
All units are A.G.A. and or C.G.A. design certified without
modifications. Refer to the 80MGF Operation and Installation Instruction Manual Information.
B−Gas Piping
Gas supply piping should not allow more than 0.5"W.C.
drop in pressure between gas meter and unit. Supply gas
pipe must not be smaller than unit gas connection.
WARNING
Shock and burn hazard.
Compounds used on gas piping threaded joints should be
resistant to action of liquefied petroleum gases.
80MGF units are equipped with a direct spark ignition system. Do not attempt to light manually.
6 − White Rodgers 36E Gas Valve −− Switch gas valve
lever to OFF. See figure 19.
Honeywell VR8205 Gas Valve −− Turn knob on gas
valve clockwise
to OFF. Do not force. See figure 20.
7 − Wait five (5) minutes to clear out any gas. If you then
smell gas, STOP! Immediately call your gas supplier
from a neighbor’s phone. Follow the gas supplier’s instructions. If you do not smell gas go to next step.
8 − White Rodgers 36E Gas Valve −− Switch gas valve lever
to ON.
Honeywell VR8205 Gas Valve −− Turn knob on gas
to ON. Do not force.
valve counterclockwise
9 − Replace access panel.
10− Turn on all electrical power to unit.
11− Set thermostat to desired setting.
12− If the appliance will not operate, follow the instructions
To Turn Off Gas To Unit" and call your service technician or gas supplier.
C−Testing Gas Piping
IMPORTANT
In case emergency shutdown is required, turn off
the main shut-off valve and disconnect the main
power to unit. These controls should be properly
labeled by the installer.
When pressure testing gas lines, the gas valve must be
disconnected and isolated. Gas valves can be damaged if
subjected to more than 0.5psig (14" W.C.). See figure 22. If
the pressure is equal to or less than 0.5psig (14"W.C.), use
the manual shut−off valve before pressure testing to isolate furnace from gas supply.
Turning Off Gas To Unit
1 − Set thermostat to lowest setting.
2 − Turn off all electrical power to unit if service is to be
performed.
3 − Remove access panel.
4 − Switch lever on White Rodgers gas valve to OFF; turn
knob on Honeywell valve clockwise
to OFF. Do not
force.
5 − Replace lower access panel.
Page 20
GAS PIPING TEST PROCEDURE
MANUAL MAIN SHUT−OFF VALVE
WILL NOT HOLD TEST PRESSURE
IN EXCESS OF 0.5 PSIG (14"W.C.)
CAP
GAS VALVE
FIELD PROVIDED
LINE PRESSURE TAP
FIGURE 22
When checking piping connections for gas leaks, use preferred means. Kitchen detergents can cause harmful corrosion on various metals used in gas piping. Use of a specialty
Gas Leak Detector is strongly recommended. It is available
through Lennox under part number 31B2001. See Corp.
8411−L10, for further details.
Do not use matches, candles, flame or any other source of
ignition to check for gas leaks.
D−Testing Gas Supply Pressure
When testing supply gas pressure, connect test gauge to
inlet pressure tap (field provided). See figure 22. Check
gas line pressure with unit firing at maximum rate. Low
pressure may result in erratic operation or underfire. High
pressure can result in permanent damage to gas valve or
overfire. For natural gas units, operating pressure at unit
gas connection must be a minimum of 4.5" W.C. For L.P.
gas units, operating pressure at unit gas connection must
be a minimum of 9.0" W.C.
On multiple unit installations, each unit should be checked
separately, with and without other units operating. Supply
pressure must fall within range listed in previous paragraph.
E−Check Manifold Pressure
After line pressure has been checked and adjusted, check
manifold pressure. Move pressure gauge to outlet pressure tap located on unit gas valve (GV1). Checks of manifold pressure are made as verification of proper regulator
adjustment. Manifold pressure for the 80MGF can be measured at any time the gas valve is open and is supplying gas
to the unit. Normal manifold pressure for natural gas units is
3.5 in. w.c. For LP/propane gas the correct manifold pressure is 9.0 in. w.c.
The gas valve is factory set and should not require adjustment. All gas valves are factory regulated. See table 12.
Manifold Adjustment Procedure:
1− Connect a test gauge to outlet pressure tap on gas
valve. Start unit and allow 5 minutes for unit to reach
steady state.
2− While waiting for the unit to stabilize, notice the flame.
Flame should be stable and should not lift from burner.
Natural gas should burn blue. L.P. gas should burn
mostly blue with some orange streaks.
3− After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to values given in
table 12.
NOTE−Shut unit off and remove manometer as soon as
an accurate reading has been obtained. Take care to
replace pressure tap plug.
F− Proper Gas Flow (Approximate)
Furnace should operate at least 5 minutes before checking gas flow. Determine time in seconds for two revolutions of gas through the meter. (Two revolutions assures
a more accurate time.) Divide by two and compare to
time in table 13 below. Adjust manifold pressure on gas
valve to match time needed.
NOTE− To obtain accurate reading, shut off all other
gas appliances connected to meter.
IMPORTANT
For safety, connect a shut-off valve between the
manometer and the gas tap to permit shut off of
gas pressure to the manometer.
TABLE 12
GAS VALVE REGULATION
Unit (Fuel)
Natural
L.P.
TABLE 13
GAS METER CLOCKING CHART
Seconds for One Revolution
Natural
LP
80mgf
g
Unit
1 cu ft
2 cu ft
1 cu ft
2 cu ft
Dial
Dial
Dial
DIAL
−45
80
160
200
400
−60
60
120
150
300
−75
48
96
120
240
−100
36
72
90
180
−120
30
60
75
150
−140
25
50
64
128
Natural−1000 btu/cu ft
Operating Pressure (outlet) in. W.C.
3.5 +0 −0.3
9.0 + 0.5
Page 21
LP−2500 btu/cu ft
the ignition control sensor connection and the negative (−) lead of the meter to the sensor wire. See figure
23.
2− Set thermostat for a heating demand and check flame
signal with unit operating. See table 16 for microamp
reading for the various control boards used.
G−High Altitude Derate
NOTE−In Canada, certification for installation at altitudes over 4500 ft. (1372m) above sea level is the jurisdiction of the local authorities.
80MGF−1 through −8 Models
This unit does not require gas pressure adjustment, or
pressure switch change when operating at elevations of 0
to 7500 ft. (0 to 2248m). Check gas line pressure with unit
firing. The minimum pressure as shown on the nameplate
for natural and propane gases must be maintained. No orifice change is required.
FLAME SIGNAL TEST
D.C. MICROAMP
METER
IGNITION
CONTROL
FLAME
SENSOR
SENSOR
WIRE
NOTE−This is the only permissible field derate for this
appliance.
FIGURE 23
80MGF−9, −10 and −11 Models
Table 14 shows manifold pressure settings for installations
at different altitudes. Refer to table 15 for pressure switch
replacement for models at elevations of 4500 feet (1372m)
and greater.
ALTITUDE
feet (m)
GAS FUEL
Natural
3.5 (0.87)
Propane/LP
9.5 (2.36)
4500 − 5500
(1372 − 1676)
Natural
3.4 (0.86)
Propane/LP
9.2 (2.29)
5500 − 6500
(1676 − 1981)
Natural
3.3 (0.82)
Propane/LP
8.9 (2.21)
6500 − 7500
(1372 − 2286)
Natural
3.2 (0.80)
Propane/LP
8.6 (2.14)
Unit Model
80MGF−45
80MGF−60
80MGF−75
80MGF−100
80MGF−120
80MGF−140
TABLE 15
Pressure Switch Part Number
No Change
No Change
88J8001
18L2401
18L2401
No Change
0 − 4500
(0 − 1372)
TABLE 16
MICROAMP
SIGNAL
DROP OUT
SIGNAL
Ram
1.0 to 5.0
t1.0
EGC
1.0 to 5.0
v.45
SureLight
w.70
v.15
CONTROL
TABLE 14
MANIFOLD
PRESSURE
in. W.C. (kPa)
SENSE"
TERMINAL
Flame signal may rise above 5 microamps for the first few
seconds after ignition then level off within the range.
WARNING
Fire and explosion hazard.
These instructions MUST be followed exactly.
Can cause a fire or explosion resulting in property
damage, personal injury or loss of life.
V−TYPICAL OPERATING CHARACTERISTICS
A−Blower Operation and Adjustment
NOTE− The following is a generalized procedure and
does not apply to all thermostat controls.
1− Blower operation is dependent on thermostat control
system.
H−Flame Signal
A microamp DC meter is needed to check the flame signal
on the primary ignition control.
Flame (microamp) signal is an electrical current which
passes from the furnace control through the sensor electrode during unit operation. Current passes from the sensor through the flame to ground to complete a safety circuit.
To Measure Flame Signal:
1− Place meter in series between furnace control and
sensor wire. Connect the positive (+) lead of meter to
2− Generally, blower operation is set at thermostat subbase fan switch. With fan switch in ON position, blower
operates continuously on heating speed. With fan
switch in AUTO position, blower cycles with demand or
runs continuously while heating or cooling circuit cycles.
3− Depending on the type of indoor thermostat, blower
and entire unit will be off when the system switch is in
OFF position.
B−Temperature Rise
Temperature rise for 80MGF units depends on unit input,
blower speed, blower horsepower and static pressure as
marked on the unit rating plate. The blower speed must be
set for unit operation within the range of AIR TEMP. RISE
°F" listed on the unit rating plate.
Page 22
TABLE 17
To Measure Temperature Rise:
1 − Place plenum thermometers in the supply and return
air plenums. Locate supply air thermometer in the first
horizontal run of the plenum where it will not pick up radiant heat from the heat exchanger.
2 − Set thermostat to highest setting.
3 − After plenum thermometers have reached their highest and steadiest readings, subtract the two readings.
The difference should be in the range listed on the unit
rating plate. If the temperature is too low, decrease
blower speed. If temperature is too high, first check
the firing rate. Provided the firing rate is acceptable, increase blower speed to reduce temperature. To
change blower speed taps see the Blower Speed Taps
section in this manual.
C−External Static Pressure
1 − Measure tap locations as shown in figure 24.
2 − Punch a 1/4" diameter hole STATIC PRESSURE
in supply and return air pleTEST
nums. Insert manometer
MANOMETER
hose flush with inside edge
of hole or insulation. Seal
around the hose with per80MGF UNIT
magum. Connect the zero
end of the manometer to the
FIGURE 24
discharge (supply) side of the system. On ducted systems, connect the other end of manometer to the return duct as above. For systems with non−ducted returns, leave the other end of the manometer open to
the atmosphere.
3 − With only the blower motor running and the evaporator
coil dry, observe the manometer reading. Adjust blower motor speed to deliver the air desired according to
the job requirements.
4 − External static pressure drop must not be more than
0.5" W.C.
5 − Seal around the hole when the check is complete.
BLOWER SPEED SELECTION
Factory Connected
Speed Taps
Unit
Speeds
Available
Cool (Black)
Heat (Red)
80MGF2-45
2
4
4
80MGF2-60
2
4
4
80MGF3-60
2
4
4
80MGF2-75
2
3
4
80MGF3-75
2
4
4
80MGF4-75
2
4
5
80MGF3/4-100
2
4
5
80MGF4/5-100
2
5
5
80MGF3/4-120
2
3
5
80MGF4/5-120
2
5
5
80MGF4/5-140
2
3
5
TABLE 18
BLOWER SPEED SELECTION
HI
LOW
◊
◊
2
◊
2
2
3
◊
3
3
4
4
4
TAPS AVAILABLE
3
4
5
5
6
5
MOTOR PLUG SPEED TAP DESIGNATION
5 − Depress harness connector tab to release wire terminal. Select connector location for new speed (refer to
unit wiring diagram). Insert wire terminal until it is securely in place. See figure 25.
6 − Replace harness connector to motor.
BLOWER SPEED TAP SELECTION
Leadless motors only
HARNESS
CONNECTOR
D−Blower Speed Taps Leadless Motors
Blower speed tap selection is accomplished by changing the
taps at the blower motor harness connector. Disconnect harness connector from motor to expose speed selectors.
Blower speed selections are listed in table 17.
To Change Blower Speed:
1 − Turn off electric power to furnace.
2 − Remove front panel and blower access door. See
figure 4.
3 − Disconnect blower motor harness from motor.
4 − Select desired speeds for heating and cooling. (Red =
heating, Black = cooling, White = common). See table
17.
Page 23
DEPRESS TAB TO RELEASE
WIRE TERMINAL. SELECT
CONNECTOR LOCATION FOR
NEW SPEED (REFER TO UNIT
WIRING DIAGRAM). INSERT
WIRE UNTIL IT IS SECURELY
IN PLACE.
FIGURE 25
MOTOR
E−Blower Speed Taps Leaded Motors
−11 Models
A−Cleaning Heat Exchanger and Burners
Blower speed tap changes are made on the SureLight
control board. See figure 8. Unused taps must be secured
on dummy terminals "PARK M1" and or "PARK M2" on the
SureLight board. The heating tap is connected to the "ACB
HEAT " terminal and the cooling tap is connected to the
"ACB COOL" terminal. The continuous blower tap is connected to the "ACB LOW" terminal.
To change existing heat tap, turn off power then switch out
speed tap on "ACB HEAT" with tap connected to "PARK
M1" or "PARK M2". See table 19 for blower motor tap colors for each speed.
TABLE 19
NOTE−Use papers or protective covering in front of furnace while cleaning furnace.
Due to dimples designed in the heatexchanger, cleaning is
not recommended. Removal is for inspection only.
Burners
Burners and burner flame should be inspected at the beginning of each heating season. Clean burners, if necessary, as outlined below:
1 − Turn off electrical and gas supply to unit.
2 − Remove burner box top.
3 − Remove burner retaining bracket.
4 − Remove burners.
5 − Clean burner insert with bottle brush as shown in figure 26.
NOTE−Use papers or protective covering in front of furnace while cleaning furnace.
CLEANING BURNERS
BURNER
BOTTLE
BRUSH
VI−MAINTENANCE
At the beginning of each heating season, the system
should be checked as follows:
Filters
All 80MGF filters are installed external to the unit. Filters
should be inspected monthly and cleaned or replaced
when necessary to assure proper furnace operation. See
table 20 for filter sizes. Replacement filters for
80MGF-45/60/75 units must have a minimum velocity rating
of
400
FPM.
Replacement
filters
for
80MGF-100/120/140 units require a minimum velocity rating of 625 FPM.
TABLE 20
MODEL NUMBER
FILTER SIZE
80MGF−45/60/75
16" X 20" X 1"
80MGF−100/120/140
20" X 20" X 1"
FIGURE 26
6 − Use bottle brush to clean inside of each burner.
7 − Replace burners and burner retaining bracket, making sure burners are properly seated in slots on tray
and orifice in manifold.
8 − Check electrode gap using appropriately sized twist
drills or feeler gauges. Gap should be between 2.79 to
3.56mm (0.110 and 0.140 inches).
9 − Reinstall burner box top.
CAUTION
Some soaps used for leak detection are corrosive
to certain metals. Carefully rinse piping thoroughly after leak test has been completed. Do not use
matches, candles, flame or other sources of ignition to check for gas leaks.
WARNING
Blower door must be securely in place when blower and burners are operating. Gas fumes, which
could contain carbon monoxide, can be drawn
into living space resulting in personal injury or
death.
10 − Restore electrical power and gas supply. Follow lighting instructions on front of unit. Check the following:
appearance of burner flame, burner pressure, gas flow
and temperature rise. Make adjustments, if necessary.
See adjustments section.
B−Supply Air Blower
1 − Check and clean blower wheel.
2 − Motors used on the Lennox 80MGF series units are
permanently lubricated and need no further lubrication.
Page 24
C−Flue and Chimney
Flue must conform to all AGA/GAMA venting requirements. Flue pipe deteriorates from the inside out and must
be disconnected in order to check thoroughly. Check flue
pipe, chimney and all connections for tightness and to
make sure there is no blockage or leaks.
D−Electrical
CAUTION
Potential for gas leaks, fire or explosion.
Some soaps used for leak detection are corrosive
to certain metals. Carefully clean piping thoroughly after leak detection has been completed.
Can cause damage to piping resulting in gas
leaks, fire or explosion.
1 − Check all wiring for loose connections.
2 − Check for correct voltage.
3 − Check amp−draw on blower motor.
HEAT EXCHANGER REMOVAL (unit shown in horizontal position)
REMOVE SCREWS (4)
Left
Back
Bottom
Top
Front
Right
SLIDE ENTIRE ASSEMBLY OUT OF CABINET
FIGURE 27
Page 25
VII−WIRING AND SEQUENCE OF OPERATION
5
3
2
6
1
4
8
7
80MGF WITH RAM CONTROL
1- When disconnect is closed, 120V is routed through
door interlock switch (S51) to feed the line voltage
side of the furnace control (A3) and transformer T1 primary. Door interlock switch must be closed for A3 and
T1 to receive voltage.
2- T1 supplies 24VAC to terminal 24VAC" on A3. In turn,
terminal R" of A3 supplies 24VAC to terminal RC" of
the indoor thermostat (not shown).
3- When there is a call for heat, W1 of the thermostat energizes W of the furnace control with 24VAC.
4- CMB BLWR of the blower control energizes the combustion air blower (B6). When the combustion air
blower nears full speed, combustion air prove switch
(S18) closes.
5- When S18 closes, assuming the flame rollout switch
(S47) primary limit (S10) and secondary limits (S21)
are closed, the furnace control begins a 45 second
time-delay (pre-purge).
6- At the end of the pre-purge cycle, the furnace control
simultaneously opens the gas valve and sends high
voltage to the spark electrode.
7- When flame is sensed, the furnace control begins a 45
second delay before energizing the indoor blower.
8- When heat demand is satisfied, W1 of the thermostat
de-energizes W of the furnace control and the furnace
control immediately de-energizes the gas valve. The
combustion air blower runs for 5 seconds (post-purge)
before being de-energized. Also, the indoor blower
runs for a designated period (90−240 seconds) as set
by switches on furnace control.
Page 26
80MGF TROUBLESHOOTING SEQUENCE
NORMAL HEATING MODE
ABNORMAL HEATING MODE
LED: SLOW FLASH RATE
THERMOSTAT CALLS FOR HEAT
LED: FAST FLASH RATE
FLAME OFF?
YES
CONTROL SELF−CHECK OKAY?
YES
HI LIMIT SWITCH CLOSED?
LOCKOUT: MAIN VALVE OFF
COMB. AIR AND SYSTEM FANS ON
RESET THERMOSTAT
LED: 5 flash if flame sensed with valve off
LED: Steady on if control board failure
NO
NO
CHECK TO SEE IF MAIN VALVE IS OFF.
SEQUENCE HOLDS UNTIL HI LIMIT CLOSES.
LED: 4 flashes.
NO
YES
PRESSURE SWITCH OPEN?
NO
YES
COMBUSTION AIR BLOWER ON?
PRESSURE SWITCH CLOSED?
CHECK TO SEE IF MAIN VALVE IS OFF.
SEQUENCE HOLDS UNTIL PRES. SWITCH OPENS.
LED: 3 flashes.
NO
CHECK TO SEE IF MAIN VALVE IS OFF.
SEQUENCE HOLDS UNTIL PRES. SWITCH CLOSES.
LED: Fast flash rate.
NO
MAIN VALVE AND SPARK ARE OFF.
INCREMENT TRIAL REGISTER
THREE TRIALS COMPLETED?
YES
PREPURGE (45 seconds)
IGNITION TRIAL (7 seconds) −− START IGNITION
SPARK, OPEN MAIN GAS VALVE. INCREMENT
TRIAL REGISTER. HAS FLAME BEEN
REGISTERED WITHIN 7 SECONDS?
YES
IGNITION RESET PERIOD
COMBUSTION & SYSTEM FANS OFF.
IS 60 MIN. RESET PERIOD COMPLETE?
LED: Fast flash rate.
YES
SYSTEM FAN ON.
(Fixed 45−second delay)
FLAME SENSE OKAY?
MAIN VALVE AND SPARK OFF.
NO
NO
YES
START IGNITION SPARK (IN 0.8 SEC. MAXIMUM).
HAS FLAME BEEN DETECTED WITHIN 7 SEC.?
FLAME CONTINUOUSLY CHECKED?
YES
ROLLOUT SWITCHES CLOSED
NO
SEQUENCE HOLDS. MAIN VALVE OFF.
COMBUSTION AND SYSTEM FANS ON.
RESET OR REPLACE ROLLOUT SWITCH.
LED: 4 flashes.
YES
HI LIMIT SWITCH CLOSED?
YES
NO
PRESSURE SWITCH CLOSED?
NO
YES
THERMOSTAT OPENS
MAIN VALVE OFF. COMBUSTION & SYSTEM FANS ON.
SEQUENCE HOLDS UNTIL SWITCH CLOSES.
LED: 4 flashes for hi limit.
LED: 3 flashes for pressure switch.
LED: SLOW FLASH RATE
SWITCH CLOSED
YES
COMB. AIR BLOWER OFF (5 sec. delay)
NO
COMBUSTION FAN ON. SYSTEM FAN OFF.
(AFTER DELAY TO OFF INTERVAL COMPLETED.)
FAN OFF (After selected 90, 120,
180, or 240 delay)?
LED: Fast flash rate.
Page 27
YES
80MGF TROUBLESHOOTING SEQUENCE − COOLING
LED: Slow flash rate.
REMAINS UNCHANGED THROUGHOUT COOLING CYCLE.
THERMOSTAT CALLS FOR COOLING.
COMPRESSOR CONTACTOR AND SYSTEM FAN
ENERGIZED AT COOLING SPEED AFTER
1 SECOND DELAY.
THERMOSTAT OPENS.
COMPRESSOR OFF.
SYSTEM FAN OFF AFTER COMPLETING
SELECTED DELAY INTERVAL
(At dip switches).
80MGF TROUBLESHOOTING SEQUENCE − FAN ONLY
LED: Slow flash rate.
REMAINS UNCHANGED THROUGHOUT SEQUENCE.
MANUAL FAN SELECTION MADE AT THERMOSTAT.
CONTROL ENERGIZES SYSTEM FAN
AT HEATING SPEED.
THERMOSTAT CALLS FOR HEAT.
YES
NO
THERMOSTAT CALLS FOR COOLING.
YES
SYSTEM FAN REMAINS ON HEATING SEQUENCE AND
RUNS THROUGH COMPLETION.
NO
SYSTEM FAN SWITCHED
TO COOLING SPEED. COOLING
SEQUENCE RUNS TO COMPLETION.
SYSTEM FAN ON AT HEATING SPEED
UNTIL MANUAL FAN IS SWITCHED
OFF AT THERMOSTAT.
SLOW FLASH
FAST FLASH
2 FLASH
3 FLASH
4 FLASH
5 FLASH
STEADY ON
LED CODES
NORMAL OPERATION. NO CALL FOR HEAT.
NORMAL OPERATION. CALL FOR HEAT.
. SYSTEM LOCKOUT. FAILURE TO DETECT OR SUSTAIN FLAME.
PRESSURE SWITCH OPEN OR CLOSED.
HIGH LIMIT OR ROLLOUT SWITCH OPEN.
FLAME SENSED AND GAS VALVE NOT ENERGIZED.
CONTROL BOARD FAILURE.
Page 28
80MGF WITH EGC−2 IGNITION CONTROL
1 − When disconnect is closed, 120V is routed through door
interlock switch (S51) to feed the line voltage side of the
ignition control (A3) and transformer T1 primary. Door interlock switch must be closed for A3 and T1 to receive
voltage.
2 − T1 supplies 24VAC to terminal 24VAC" on A3. In turn,
terminal R" of A3 supplies 24VAC to terminal R" of the
indoor thermostat (not shown).
3 − When there is a call for heat, W1 of the thermostat energizes W of the ignition control with 24VAC.
4 − CAB of the ignition control energizes the combustion air
blower (B6). When the combustion air blower nears
full speed, combustion air prove switch (S18)
closes.
5 − When S18 closes, assuming primary limit (S10) and
secondary limit (S21) are closed, a 15 second pre−purge
begins. After the pre−purge period the ignition control
starts ignition spark and opens main gas valve.
6 − After 45 seconds, ignition control (A3) energizes the
indoor blower (B3).
7 − When heat demand is satisfied, W1 of the thermostat deenergizes W of the ignition control and the gas valve is
immediately de-energized. The combustion air blower
immediately stops. The indoor blower runs for a designated fan off" period (60−240 seconds) as set by jumper
on ignition control.
Page 29
80MGF WITH EGC−2 HEATING SEQUENCE OF OPERATION
ABNORMAL HEATING MODE
NORMAL HEATING MODE
GAS VALVE OFF. COMB. BLOWER ON. INDOOR
BLOWER ON HEAT SPEED. SEQUENCE HOLDS UNTIL
NO FLAME SENSED OR MAIN POWER IS INTERRUPTED
AND RESET. DIAG. CODE: 1− FLASHING; 2−OFF
(FLAME SENSED WITHOUT VALVE ENERGIZED)
CONTROL MAIN POWER ON"
FLAME OFF?
NO
YES
CONTROL SELF−CHECK OKAY?
YES
ROLL−OUT SWITCH CLOSED
NO
GAS VALVE, COMB. BLOWER AND INDOOR BLOWER
(WITH DELAY) OFF. REMOVE POWER TO RESET
CONTROL. DIAG. CODE: BOTH ON (CONTROL
SELF−CHECK FAILURE OR INCORRECT WIRING)
NO
YES
LED: SLOW FLASH RATE
GAS VALVE, COMB. BLOWER AND INDOOR BLOWER
(WITH DELAY) OFF. SEQUENCE HOLDS UNTIL
ROLL−OUT SWITCH IS MANUALLY CLOSED.
DIAG. CODE: 1−ON;
2−FLASHING (FLAME ROLL−OUT OPEN)
THERMOSTAT CALLS FOR HEAT
LED: FAST FLASH RATE
COMB. AIR BLOWER PRESSURE SWITCH OPEN?
YES
COMBUSTION AIR BLOWER ON?
HTG ACC. TERM. ENERGIZED.
YES
PRESSURE SWITCH CLOSED WITHIN 2.5 MIN.?
NO
GAS VALVE, COMB. BLOWER AND INDOOR BLOWER
(WITH DELAY) OFF. SEQUENCE HOLDS UNTIL
PRESSURE SWITCH CLOSES OR THERMOSTAT
RESETS CONTROL. DIAG. CODE: 1−OFF;
2−FLASHING (C.A.B. PRESSURE SWITCH OPEN)
NO
YES
YES
COMB. AIR BLOWER PREPURGE (15 seconds)
IGNITION TRIAL (10 seconds) −− START IGNITION
SPARK, OPEN MAIN GAS VALVE.
HAS FLAME REGISTERED WITHIN 10 SECONDS
AFTER IGNITION TRIAL?
YES
IS FLAME SENSED AFTER 10 SECOND
FLAME RECTIFICATION PERIOD?
YES
GAS VALVE OFF. COMB. BLOWER ON. INDOOR
BLOWER (WITH 45 DELAY) ON. HAS CONTROL FAILED
FLAME SENSE 5 TIMES DURING ONE HEAT DEMAND?
IF YES, SYSTEM GOES INTO 60 MIN.WATCHGUARD.
DIAG. CODE: 1−ALT. FLASHING / 2−ALT. FLASHING IF
NO, GO TO COMB. AIR BLOWER ON?"
NO
NO
HAS CONTROL RESET IGNITION SEQUENCE 5 TIMES
IF YES, SYSTEM GOES INTO 60 MIN. WATCHGUARD.
DIAG. CODE: 1−ALT. FLASHING / 2−ALT. FLASHING IF
NO, GO TO COMB. AIR BLOWER ON?"
INDOOR AIR BLOWER ON.
(Fixed 45−second delay)
PRIMARY/SECONDARY LIMITS MONITORED IN
HEAT CYCLE. ARE SWITCHES CLOSED?
NO
GAS VALVE OFF. COMB. BLOWER OFF. INDOOR
BLOWER ON UNTIL LIMIT CLOSES. DIAG.
CODE: 1−FLASHING / 2−ON (LIMIT OPEN)
IS LIMIT NOW CLOSED?
YES
YES
PRESSURE SWITCH CLOSED?
PRESSURE SWITCH WATCHGUARD CONDITION:
GAS VALVE, COMB. BLOWER AND INDOOR BLOWER
(WITH DELAY) OFF. DIAG. CODE: 1−OFF /
2−FLASHING (C.A.B. PRESSURE SWITCH OPEN) IS 5
MINUTE RESET PERIOD COMPLETE?
NO
YES
HAS PRIMARY LIMIT OPENED 5 TIMES DURING
ONE UNSATISFIED HEAT DEMAND. IF YES,
SYSTEM GOES INTO 60 MIN.WATCHGUARD.
DIAG. CODE: 1−FLASHING / 2−ON
IF NO, GO TO COMB. AIR BLOWER ON?"
THERMOSTAT OPENS
LED: SLOW FLASH RATE
COMB. AIR BLOWER OFF (5 sec. delay)
HTG ACC. TERM.DE−ENERGIZED.
GAS VALVE, COMB. BLOWER AND INDOOR BLOWER
(WITH DELAY) OFF. DIAG. CODE: 1−OFF / 2−FLASHING NO
(C.A.B. PRESSURE SWITCH OPEN) HAS C.A.B.
PRESSURE SWITCH CLOSED IN 2.5 MINUTES?
INDOOR AIR BLOWER OFF (After selected 60, 90,
120, 180, or 240 delay)?
YES
Page 30
80MGF WITH EGC−2 COOLING SEQUENCE OF OPERATION
LED: Slow flash rate.
REMAINS UNCHANGED THROUGHOUT COOLING CYCLE.
THERMOSTAT CALLS FOR COOLING.
COMPRESSOR CONTACTOR AND SYSTEM FAN
ENERGIZED AT COOLING SPEED AFTER
1 SECOND DELAY. ACC TERMINAL ENERGIZED.
THERMOSTAT OPENS.
COMPRESSOR OFF.
SYSTEM FAN AND ACC TERMINAL OFF AFTER
0 SECONDS.
80MGF WITH EGC−2 MANUAL CONTINUOUS FAN SEQUENCE OF OPERATION
LED: Slow flash rate.
REMAINS UNCHANGED THROUGHOUT SEQUENCE.
CONTINUOUS FAN SELECTION MADE AT THERMOSTAT.
CONTROL ENERGIZES SYSTEM FAN AT HEAT SPEED.
ACC TERMINAL ENERGIZED.
HTG ACC. TERM. ENERGIZED
WITH COMB. AIR BLOWER.
THERMOSTAT CALLS FOR HEAT.
YES
NO
SYSTEM FAN REMAINS ON HEATING SPEED AFTER
SELECTED DELAY. ACC TERM. REMAINS ENERGIZED.
THERMOSTAT CALLS FOR COOLING.
YES
NO
SYSTEM FAN SWITCHED TO COOLING
SPEED. ACC TERMINAL REMAINS ENERGIZED.
THERMOSTAT OPENS.
SYSTEM FAN SWITCHED OFF AFTER DELAY.
ACC TERMINAL DE−ENERGIZED.
THERMOSTAT OPENS.
SYSTEM FAN SWITCHES TO CONTINUOUS SPEED
AND ENERGIZES ACC TERMINAL. BOTH REMAIN ON
UNTIL CONTINUOUS FAN IS SWITCHED OFF AT THERMOSTAT.
Page 31
80MGF WITH EGC−1 IGNITION CONTROL
1 − When disconnect is closed, 120V is routed through door
interlock switch (S51) to feed the line voltage side of the
ignition control (A3) and transformer T1 primary. Door interlock switch must be closed for A3 and T1 to receive
voltage.
2 − T1 supplies 24VAC to terminal 24VAC" on A3. In turn,
terminal R" of A3 supplies 24VAC to terminal R" of the
indoor thermostat (not shown).
3 − When there is a call for heat, W1 of the thermostat energizes W of the ignition control with 24VAC.
4 − CAB of the ignition control energizes the combustion air
blower (B6). When the combustion air blower nears
full speed, combustion air prove switch (S18)
closes.
5 − When S18 closes, assuming primary limit (S10) and
secondary limit (S21) are closed, a 15 second pre−purge
begins. After the pre−purge period the ignition control
starts ignition spark and opens main gas valve.
6 − After 45 seconds, ignition control (A3) energizes the
indoor blower (B3).
7 − When heat demand is satisfied, W1 of the thermostat deenergizes W of the ignition control and the gas valve is
immediately de-energized. The combustion air blower
immediately stops. The indoor blower runs for a designated fan off" period (60−240 seconds) as set by jumper
on ignition control.
Page 32
80MGF WITH EGC−1 HEATING SEQUENCE OF OPERATION
ABNORMAL HEATING MODE
NORMAL HEATING MODE
GAS VALVE OFF. COMB. BLOWER ON. INDOOR
BLOWER ON HEAT SPEED. SEQUENCE HOLDS UNTIL
NO FLAME SENSED OR MAIN POWER IS INTERRUPTED
AND RESET. DIAG. CODE: 1− FLASHING; 2−OFF
(FLAME SENSED WITHOUT VALVE ENERGIZED)
CONTROL MAIN POWER ON"
FLAME OFF?
NO
YES
CONTROL SELF−CHECK OKAY?
YES
ROLL−OUT SWITCH CLOSED
NO
GAS VALVE, COMB. BLOWER AND INDOOR BLOWER
(WITH DELAY) OFF. REMOVE POWER TO RESET
CONTROL. DIAG. CODE: BOTH ON (CONTROL
SELF−CHECK FAILURE OR INCORRECT WIRING)
NO
YES
LED: SLOW FLASH RATE
GAS VALVE, COMB. BLOWER AND INDOOR BLOWER
(WITH DELAY) OFF. SEQUENCE HOLDS UNTIL
ROLL−OUT SWITCH IS MANUALLY CLOSED.
DIAG. CODE: 1−ON;
2−FLASHING (FLAME ROLL−OUT OPEN)
THERMOSTAT CALLS FOR HEAT
LED: FAST FLASH RATE
COMB. AIR BLOWER PRESSURE SWITCH OPEN?
NO
YES
GAS VALVE, COMB. BLOWER AND INDOOR BLOWER
(WITH DELAY) OFF. SEQUENCE HOLDS UNTIL
PRESSURE SWITCH CLOSES OR THERMOSTAT
RESETS CONTROL. DIAG. CODE: 1−OFF;
2−FLASHING (C.A.B. PRESSURE SWITCH OPEN)
COMBUSTION AIR BLOWER ON?
HTG ACC. TERM. ENERGIZED?
YES
PRESSURE SWITCH CLOSED WITHIN 2.5 MIN.?
YES
COMB. AIR BLOWER PREPURGE (15 seconds)
NO
YES
IGNITION TRIAL (10 seconds) −− START IGNITION
SPARK, OPEN MAIN GAS VALVE.
HAS FLAME REGISTERED WITHIN 10 SECONDS
AFTER IGNITION TRIAL?
YES
IS FLAME SENSED AFTER 10 SECOND
FLAME RECTIFICATION PERIOD?
YES
GAS VALVE OFF. COMB. BLOWER ON. INDOOR
BLOWER (WITH 45 DELAY) ON. HAS CONTROL FAILED
FLAME SENSE 5 TIMES DURING ONE HEAT DEMAND?
IF YES, SYSTEM GOES INTO 60 MIN.WATCHGUARD.
DIAG. CODE: 1−ALT. FLASHING / 2−ALT. FLASHING IF
NO, GO TO COMB. AIR BLOWER ON?"
NO
NO
HAS CONTROL RESET IGNITION SEQUENCE 5 TIMES
IF YES, SYSTEM GOES INTO 60 MIN. WATCHGUARD.
DIAG. CODE: 1−ALT. FLASHING / 2−ALT. FLASHING IF
NO, GO TO COMB. AIR BLOWER ON?"
INDOOR AIR BLOWER ON.
(Fixed 45−second delay)
PRIMARY/SECONDARY LIMITS MONITORED IN
HEAT CYCLE. ARE SWITCHES CLOSED?
NO
GAS VALVE OFF. COMB. BLOWER OFF. INDOOR
BLOWER ON UNTIL LIMIT CLOSES. DIAG.
CODE: 1−FLASHING / 2−ON (LIMIT OPEN)
IS LIMIT NOW CLOSED?
YES
YES
PRESSURE SWITCH CLOSED?
PRESSURE SWITCH WATCHGUARD CONDITION:
GAS VALVE, COMB. BLOWER AND INDOOR BLOWER
(WITH DELAY) OFF. DIAG. CODE: 1−OFF /
2−FLASHING (C.A.B. PRESSURE SWITCH OPEN) IS 5
MINUTE RESET PERIOD COMPLETE?
NO
YES
HAS PRIMARY LIMIT OPENED 5 TIMES DURING
ONE UNSATISFIED HEAT DEMAND. IF YES,
SYSTEM GOES INTO 60 MIN.WATCHGUARD.
DIAG. CODE: 1−FLASHING / 2−ON
IF NO, GO TO COMB. AIR BLOWER ON?"
THERMOSTAT OPENS
LED: SLOW FLASH RATE
COMB. AIR BLOWER OFF (5 sec. delay)
HTG ACC. TERM. DE−ENERGIZED.
GAS VALVE, COMB. BLOWER AND INDOOR BLOWER
(WITH DELAY) OFF. DIAG. CODE: 1−OFF / 2−FLASHING NO
(C.A.B. PRESSURE SWITCH OPEN) HAS C.A.B.
PRESSURE SWITCH CLOSED IN 2.5 MINUTES?
INDOOR AIR BLOWER OFF (After selected 60, 90,
120, 180, or 240 delay)?
YES
Page 33
80MGF WITH EGC−1 COOLING SEQUENCE OF OPERATION
LED: Slow flash rate.
REMAINS UNCHANGED THROUGHOUT COOLING CYCLE.
THERMOSTAT CALLS FOR COOLING.
COMPRESSOR CONTACTOR AND SYSTEM FAN
ENERGIZED AT COOLING SPEED AFTER
1 SECOND DELAY. ACC TERMINAL ENERGIZED.
THERMOSTAT OPENS.
COMPRESSOR OFF.
SYSTEM FAN AND ACC TERMINAL OFF AFTER
0 SECONDS.
80MGF WITH EGC−1 MANUAL CONTINUOUS FAN SEQUENCE OF OPERATION
LED: Slow flash rate.
REMAINS UNCHANGED THROUGHOUT SEQUENCE.
CONTINUOUS FAN SELECTION MADE AT THERMOSTAT.
CONTROL ENERGIZES SYSTEM FAN AT LOW SPEED.
ACC TERMINAL ENERGIZED.
HTG ACC. TERM. ENERGIZED
WITH COMB. AIR BLOWER.
THERMOSTAT CALLS FOR HEAT.
YES
NO
SYSTEM FAN SWITCHES TO HEAT SPEED AFTER
SELECTED DELAY. ACC TERM. REMAINS ENERGIZED.
THERMOSTAT CALLS FOR COOLING.
YES
NO
SYSTEM FAN SWITCHED TO COOLING
SPEED. ACC TERMINAL REMAINS ENERGIZED.
THERMOSTAT OPENS.
SYSTEM FAN SWITCHED OFF AFTER DELAY.
ACC TERMINAL DE−ENERGIZED.
THERMOSTAT OPENS.
SYSTEM FAN SWITCHES TO CONTINUOUS SPEED
AND ENERGIZES ACC TERMINAL. BOTH REMAIN ON
UNTIL CONTINUOUS FAN IS SWITCHED OFF AT THERMOSTAT.
Page 34
80MGF WITH SURELIGHT IGNITION CONTROL
1 − When there is a call for heat, W1 of the thermostat energizes W of the furnace control with 24VAC.
2 − S10 primary limit switch and S47 rollout switch are
closed. Call for heat can continue.
3 − SureLight control energizes combustion air blower
B6. Combustion air blower runs until S18 combustion
air prove switch closes (switch must close within 2−1/2
minutes or control goes into 5 minute Watchguard
Pressure Switch delay). Once S18 closes, a 15−second pre−purge follows.
4 − SureLight control energizes ignitor. A 20−second
warm−up period begins.
5 − Gas valve opens for a 4−second trial for ignition.
6 − Flame is sensed, gas valve remains open for the heat
call.
7 − After 45−second delay, SureLight control energizes
indoor blower B3.
8 − When heat demand is satisfied, W1 of the indoor thermostat de−energizes W of the SureLight control which
de−energizes the gas valve. Combustion air blower
B6 continues a 5−second post−purge period, and indoor blower B3 completes a selected OFF time delay.
Page 35
SURELIGHT CONTROL
HEATING SEQUENCE OF OPERATION
NORMAL HEATING MODE
ABNORMAL HEATING MODE
POWER ON
GAS VALVE OFF. COMBUSTION AIR BLOWER ON.
INDOOR BLOWER ON.
LED #1 ALTERNATING FAST FLASH
LED#2 ALTERNATING FAST FLASH
CHECK FOR BROKEN IGNITOR OR
OPEN IGNITOR CIRCUIT
CONTROL SELF−CHECK OKAY?
NO
COMBUSTION AIR BLOWER ON FOR 1 SECOND.
GAS VALVE OFF. COMBUSTION AIR BLOWER OFF.
INDOOR BLOWER DELAY OFF.
LED #1 ON
LED #2 ON
(RESET CONTROL BY TURNING MAIN POWER OFF.)
YES
TURN INDUCER ON FOR 1 SECOND.
IS POLARITY REVERSED?
SIGNAL IMPROPER
GROUND AT LED.
SIGNAL HOLDS
UNTIL UNIT IS
PROPERLY
GROUNDED.
POLARITY REVERSED.
LED #1 −− FAST FLASH
LED #2 −− SLOW FLASH
NO
NO
YES
IS THERE
PROPER GROUND?
IS VOLTAGE
ABOVE 75 VOLTS?
NO
LOW VOLTAGE SIGNAL AT LED HOLDS
UNTIL VOLTAGE RISES ABOVE 75 VOLTS.
YES
NO
ROLLOUT SWITCH CLOSED?
YES
GAS VALVE OFF. COMBUSTION AIR BLOWER OFF.
INDOOR BLOWER OFF WITH DELAY.
LED #1 −− ON. LED #2 −− SLOW FLASH.
SEQUENCE HOLDS UNTIL ROLLOUT SWITCH CLOSES.
GAS VALVE OFF. COMBUSTION AIR BLOWER ON.
INDOOR BLOWER ON HEATING SPEED.
LED #1 −− SLOW FLASH
LED #2 −− OFF
NO
BURNER OFF?
(CONTINUOUS FLAME CHECK)
YES
NORMAL OPERATION:
LED #1 −− SLOW FLASH
LED #2 −− SLOW FLASH
THERMOSTAT CALLS FOR HEAT:
LED #1 −− FAST FLASH
LED #2 −− FAST FLASH
YES
NO
IS COMBUSTION AIR
PRESSURE SWITCH OPEN?
YES
IS COMBUSTION AIR BLOWER ENERGIZED?
(HTG ACC TERMINAL IS ENERGIZED WITH C.A.B.)
YES
NO
HAS COMBUSTION AIR PRESSURE
SWITCH CLOSED IN 2.5 MINUTES?
YES
15-SECOND COMBUSTION AIR BLOWER PREPURGE
INITIATED BY CLOSED PRESSURE SWITCH.
YES
CONTINUED NEXT PAGE
Page 36
GAS VALVE OFF.
COMBUSTION AIR BLOWER OFF.
INDOOR BLOWER OFF WITH DELAY.
LED #1 OFF
LED #2 SLOW FLASH
(Sequence holds until pressure switch
closes or thermostat resets control.)
PRESSURE SWITCH IS IN WATCHGUARD MODE.
GAS VALVE OFF. COMBUSTION AIR BLOWER OFF.
INDOOR BLOWER OFF WITH DELAY.
LED #1 −− OFF. LED #2 −− SLOW FLASH.
IS 5-MINUTE RESET PERIOD COMPLETE?
NORMAL HEATING MODE
ABNORMAL HEATING MODE
15-SECOND COMBUSTION AIR INDUCER PREPURGE
INITIATED BY CLOSED PRESSURE SWITCH.
NO
IS VOLTAGE ABOVE 75 VOLTS?
YES
IS THERE A PROPER GROUND?
YES
YES
YES
NO
IGNITOR WARM-UP −− 20 SECONDS.
YES
NO
NO
LEDS SIGNAL
ALTERNATING
FAST FLASH
IS IGNITOR INTACT AND CONNECTED?
4-SECOND TRIAL FOR IGNITION.
GAS VALVE OPENS. IGNITOR ENERGIZED FOR
1 SECOND AFTER VALVE OPENS.
NO FLAME SENSED DURING THIS PERIOD.
BOARD 97L48 ONLY: IGNITOR ENERGIZED FOR THE
FULL 4−SECOND TRIAL FOR IGNITION.
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
INDOOR BLOWER OFF.
NO HAS CONTROL FAILED TO SENSE FLAME FOR
FIVE CONSECUTIVE TRIES DURING A SINGLE
HEAT DEMAND?
YES
NO
YES
FLAME STABILIZATION PERIOD.
4 SECONDS
FLAME RECTIFICATION CURRENT
CHECK. CAN FLAME BE PROVEN WITHIN
4 SECONDS AFTER GAS VALVE OPENS?
(u0.15 microamps)
IGNITION WATCHGUARD MODE. GAS VALVE OFF.
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF WITH DELAY
LED 1 ALT. SLOW FLASH LED 2 ALT SLOW FLASH
IS 60-MINUTE RESET PERIOD COMPLETE?
YES
YES
NO
YES
LOW FLAME SIGNAL
(Does not affect operation of control)
LED #1 −− SLOW FLASH
LED #2 −− FAST FLASH
NO
FLAME SIGNAL ABOVE 0.7 MICROAMPS?
YES
INDOOR BLOWER ON DELAY BEGINS
(45 seconds.)
YES
NO
PRIMARY AND SECONDARY LIMIT
SWITCHES CLOSED?
NO
HAS CONTROL RESET IGNITION
SEQUENCE FOUR TIMES?
FLAME PRESENT?
GAS VALVE DE−ENERGIZED.
COMBUSTION AIR INDUCER
DE−ENERGIZED.INDOOR BLOWER
ON UNTIL SWITCH CLOSES.LED #1
−− SLOW FLASH. LED #2 −− ON.
IS LIMIT SWITCH CLOSED?
YES
LIMIT SWITCH WATCH GUARD
MODE. GAS VALVE OFF.
COMB. AIR INDUCER OFF. INDOOR BLOWER OFF WITH
DELAY. LED#1−SLOW FLASH
LED#2− ON. IS 60MINUTE RESET PERIOD COMPLETE.?
YES
NO
YES
HAS PRIMARY/SECONDARY LIMIT RESET.
(See table 9 DIAGNOSTIC CODES for limit reset operation)
GAS VALVE POWER OFF.
COMBUSTION AIR INDUCER POWER OFF.
INDOOR BLOWER OFF WITH DELAY
LED #1 −− ON. LED #2 −− SLOW FLASH.
SEQUENCE HOLDS UNTIL ROLLOUT SWITCH IS RESET
NO
ROLLOUT SWITCH CLOSED?
YES
COMBUSTION AIR PRESSURE
SWITCH CLOSED?
YES
THERMOSTAT DEMAND SATISFIED.
YES
LED #1 & #2 SIMULTANEOUS SLOW FLASHES.
YES
NO
YES
GAS VALVE DE−ENERGIZED.
COMBUSTION AIR INDUCER ON.
INDOOR BLOWER OFF WITH DELAY
LED #1 −− OFF. LED #2 −− SLOW FLASH.
HAS CAB SWITCH CLOSED IN 2.5 MINUTES?
NO
YES
COMB. AIR INDUCER CONTINUES 5-SECOND POST PURGE
AFTER T’STAT DEMAND IS SATISFIED. INDOOR AIR BLOWER
COMPLETES SELECTED OFF" DELAY BEFORE SHUTTING OFF.
ACB.HEAT SPEED, HTG ACC TERM. AND ACC TERM. OFF.
Page 37
5-MINUTE PRESSURE SWITCH
WATCHGUARD MODE.
YES
SURELIGHT CONTROL
COOLING SEQUENCE OF OPERATION
NORMAL COOLING MODE
ABNORMAL COOLING MODE
POWER ON
IGNITION CONTROL MAIN POWER ON.
GAS VALVE OFF. COMBUSTION AIR BLOWER OFF.
INDOOR BLOWER OFF WITH NORMAL DELAY.
SIGNAL CIRCUIT BOARD FAILURE AT LED.
INTERRUPT MAIN POWER TO RESET CONTROL.
NO
CONTROL SELF DIAGNOSTIC CHECK.
IS CONTROL OPERATING NORMALLY?
YES
TURN INDUCER ON FOR 1 SECOND.
YES
IS POLARITY REVERSED?
SIGNAL IMPROPER
GROUND AT LED.
SIGNAL HOLDS
UNTIL UNIT IS
PROPERLY
GROUNDED.
SIGNAL POLARITY REVERSED AT LED.
NO
NO
YES
IS THERE
PROPER GROUND?
IS VOLTAGE
ABOVE 75 VOLTS?
ROLLOUT SWITCH MONITORED CONTINUOUSLY.
IS ROLLOUT SWITCH CLOSED?
NO
LOW VOLTAGE SIGNAL AT LET HOLDS
UNTIL VOLTAGE RISES ABOVE 75 VOLTS.
NO
GAS VALVE OFF. COMBUSTION AIR BLOWER OFF.
INDOOR BLOWER OFF WITH NORMAL DELAY.
SIGNAL CIRCUIT BOARD FAILURE AT LED.
SEQUENCE HOLDS UNTIL ROLLOUT SWITCH CLOSES.
NO
GAS VALVE OFF. COMBUSTION AIR BLOWER OFF.
INDOOR BLOWER OFF WITH NORMAL DELAY.
SIGNAL CIRCUIT BOARD FAILURE AT LED.
SEQUENCE HOLDS UNTIL FLAME IS NOT SENSED.
YES
CHECK FOR MAIN BURNER FLAME SENSE.
IS MAIN BURNER FLAME OFF?
LED: SLOW FLASH RATE REMAINS UNCHANGED
THROUGHOUT COOLING CYCLE.
THERMOSTAT CALLS FOR COOLING.
COMPRESSOR CONTACTOR AND SYSTEM FAN
ENERGIZED WITH 0-SECOND DELAY. ACB COOL
SPEED AND ACC. TERMINAL IS ENERGIZED.
THERMOSTAT OPENS.
COMPRESSOR OFF.
SYSTEM FAN AND ACC. TERM. OFF
WITH 0-SECOND DELAY.
Page 38
SURELIGHT CONTROL
CONTINUOUS LOW SPEED FAN SEQUENCE OF OPERATION
LED: SLOW FLASH RATE REMAINS
UNCHANGED THROUGHOUT SEQUENCE.
MANUAL FAN SELECTION MADE AT THERMOSTAT.
CONTROL (G) ENERGIZES SYSTEM FAN AT ACB
LOW SPEED. ACC. TERMINAL IS ENERGIZED.
THERMOSTAT CALLS FOR HEAT (W).
NO
HTG ACC. TERM. ENERGIZES
WITH COMB. AIR BLOWER.
YES
BOARD NO. 63K8901
SYSTEM FAN DE−ENERGIZED. SYSTEM FAN
ENERGIZES ON ACB HEAT SPEED AFTER
NORMAL DELAY.
THERMOSTAT CALLS FOR COOLING.
NO
YES
BOARD NO. 24L85, 56L83, 97L48
SYSTEM FAN SWITCHES TO ACB HEAT SPEED
AFTER NORMAL DELAY (fan remains energized)
SYSTEM FAN SWITCHED TO ACB COOL
SPEED. ACC. TERM. REMAINS ON.
THERMOSTAT OPENS. COMBUSTION AIR
AND HTG ACC TERMINAL DE−ENERGIZE.
THERMOSTAT OPENS.
BOARD 63K89: SYSTEM FAN OFF. ACC. TERM.
OFF. (AFTER OFF DELAY COMPLETED).
BOARDS 24L85, 56L83 AND 97L48:
SYSTEM FAN SWITCHES TO
LOW SPEED AFTER NORMAL DELAY.
(fan remains energized)
MANUAL FAN SELECTION MADE AT THERMOSTAT.
CONTROL (G) ENERGIZES SYSTEM FAN AT ACB
LOW SPEED. ACC. TERM. ENERGIZED.
Page 39
VIII−Troubleshooting−SureLight Control
PROBLEM: 1 UNIT FAILS TO OPERATE IN THE COOLING, HEATING, OR CONTINUOUS FAN MODE
Condition
Possible Cause
1.1
1.1.1
− Both diagnostic lights fail to light up. Main voltage 120V not supplied to
unit.
LED#1−Off
LED#2−Off
ACTION 1 − Check for correct wiring of 120V to
power make up box and transformer.
ACTION 2 − Check 24V wiring to control board.
1.1.3
Circuit breaker tripped or fails to
close.
ACTION 1 − Replace circuit breaker if it is reset
but does not have continuity.
ACTION 2 − If circuit breaker still trips, check for
short.
1.1.4
Door interlock switch failure.
ACTION 1 − Check that door switch is activated
when door is closed.
ACTION 2 − Check wire connections to switch, replace loose connectors.
ACTION 3 − Check continuity of switch in closed
position. Replace if malfunctioning
1.1.5
Transformer Failure.
ACTION 1 − Check that transformer output is
24V. Replace if malfunctioning
Failed control board.
− Diagnostic lights flash the roll−out
code.
LED#1−On,
LED#1
O
LED#2−Slow
LED#2
Slow Flash
1.3
− On initial power−up the comb. air
blower does not energize.
− Diagnostic lights flash the reverse
polarity code.
ACTION 1 − Check 120V main voltage.
Determine cause of main power failure.
1.1.2
Miswiring of furnace or improper
connections.
1.1.6
1.2
Corrective Action / Comments
1.2.1
Roll−out switch open.
ACTION 1 − If all the above items have been
checked, replace board.
ACTION 1 − Manually reset the roll−out switch
by pushing the top button.
ACTION 2 − Determine the cause of the roll−out
switch activation before leaving furnace.
1.2.2
Roll−out switch failure.
ACTION 1 − Check continuity across roll−out
switch. Replace roll−out switch if switch is reset
but does not have continuity.
1.2.3
Mis iring or improper connections at
Miswiring
roll−out switch.
ACTION 1 − Check wiring connections to switch.
switch
1.2.4
Nine pin connector failure
ACTION 1 − Check 9−pin connector for proper
connection to control board.
ACTION 2 − Check continuity of the multi plug
pin.
1.3.1
120V main power polarity reversed.
ACTION 1 − Check the 120V has line and neutral
correctly input into control.
ACTION 2 − Reverse the line and neutral at the
120V field connection.
LED#1−Fast Flash,
LED#2−Slow Flash.
1.4
1.4.1
− On initial power up the combustion
Open combustion air blower motor
air blower does not energize.
− Diagnostic lights flash normal power circuit.
on operation.
LED#1−Slow Flash
LED#2−Slow Flash
1.4.2
Failed combustion air blower motor.
Page 40
ACTION 1 − Check for 120V to combustion air
blower. If no power, check wire and connections.
ACTION 1 − If power is present at blower, replace
blower.
PROBLEM 1: UNIT FAILS TO OPERATE IN THE COOLING, HEATING, OR CONTINUOUS FAN MODE
Condition
1.5
− On initial power−up the combustion
air blower remains energized.
g
− Diagnostic
Di
ti lilights
ht flflash
h th
the iimproper
main ground.
LED#1−Alternating Fast Flash
LED#2−Alternating Fast Flash
Possible Cause
Corrective Action / Comments
1.5.1
Improper ground to the unit.
ACTION 1 − Check that the unit is properly
grounded.
ACTION 2 − Install a proper main ground to the
unit
1.5.2
6−Pin connector is improperly attached to the circuit board.
ACTION 1 − Check 6−pin connector for proper
installation. Correctly insert connector into control.
1.5.3
Line voltage is below 75V.
ACTION 1 − Check that the line voltage is above
75V. Determine cause of voltage drop and supply correct voltage to the control.
PROBLEM 2: UNIT FAILS TO OPERATE IN THE COOLING OR HEATING MODE, BUT COMBUSTION AIR BLOWER OPERATES CONTINUOUS. UNITS WITH CONTROL BOARDS DATE CODED
AFTER NOV.1 1997, WILL OPERATE IN COOLING WITH COMBUSTION AIR BLOWER CYCLING
5 SECONDS ON 55 SECONDS OFF, BUT NOT IN THE HEATING MODE.
Condition
2.1
− On initial power−up the combustion
air blower remains energized.
− Diagnostic lights flash the improper
main ground.
− Units with control boards date
coded after Nov.1
Nov 1 1997; combustion
air blower will cycle 5 seconds on 55
seconds off.
Possible Cause
Corrective Action / Comments
2.1.1
Open ignitor circuit.
ACTION 1 − Check for correct wiring and loose
connections in the ignitor circuit. Check multi −
plug connections for correct installation.
2.1.2
Broken or failed ignitor.
ACTION 1 − Unplug ignitor and read resistance
across ignitor. If resistance does not read between 10.9 and 19.7 ohms, replace the ignitor.
LED#1−Alternating Fast Flash
LED#2−Alternating Fast Flash
PROBLEM 3: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER DOES
NOT ENERGIZE
Condition
3.1
− Unit operates with a cooling or continuous fan demand.
− Combustion air blower will not start
with a Heating demand.
− Diagnostic
g
lights
g
flash the limit failure
mode.
d
LED#1−Slow Flash,
LED#2−On
Possible Cause
Corrective Action / Comments
3.1.1
Primary or secondary (if equipped)
limit open.
ACTION 1 − Check continuity across switch(es).
Switches reset automatically upon cool down.
ACTION 2 − Check for restrictions on blower inlet
air (including filter) and outlet air. Determine
cause for limit activation before placing unit back
in operation.
3.1.2
Miswiring of furnace or improper connections at limit switch(es).
ACTION 1 − Check for correct wiring and loose
connections. Correct wiring and/or replace any
loose connections.
3.2
3.2.1
− Unit operates with a cooling and continuous fan demand.
Miswiring of furnace or improper con− Combustion air blower will not start
nections to combustion air blower.
with a Heating demand.
− Diagnostic lights flash the pressure
switch failure code.
LED#1−Off,
LED#2−Slow Flash
3.2.2
Pressure switch stuck closed.
Page 41
ACTION 1 − Check for correct wiring and loose
connections. Correct wiring and/or replace any
loose connections.
ACTION 1 − Check that the pressure switch is
open without the combustion air blower operating. Replace if malfunctioning
PROBLEM 3: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER DOES
NOT ENERGIZE (CONT.).
Condition
Possible Cause
3.3
− Unit operates with a cooling and con3.3.1
tinuous fan demand.
Miswiring of furnace or improper con− Combustion air blower will not start
nections to combustion air blower.
with a Heating demand.
− Diagnostic lights flash the pressure
switch failure code 2.5
2 5 minutes after
heating demand.
3.3.2
Combustion air blower failure.
LED#1−Off,
LED#2−Slow Flash
Corrective Action/Comments
ACTION 1 − Check for correct wiring and loose
connections. Correct wiring and/or replace any
loose connections.
ACTION 1 − If there is 120V to combustion air
blower and it does not operate, replace combustion air blower.
PROBLEM 4: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER
ENERGIZES, IGNITOR IS NOT ENERGIZED.
Condition
Possible Cause
Corrective Action/Comments
4.1
− Unit operates with a cooling and
continuous fan demand.
− Combustion air blower energizes
with a heating demand.
demand
− Diagnostic lights flash the pressure
switch failure code 2.5 minutes after
heating demand.
4.1.1
Pressure switch does not close due
to incorrect routing of the pressure
switch tubing.
ACTION 1 − Check that the pressure switch tubing is correctly routed. Correctly route pressure
switch tubing.
4.1.2
Pressure switch does not close due
to obstructions in the pressure tubing.
ACTION 1 − Remove any obstructions from the
pressure tubing and/or taps.
4.1.3
Pressure switch tubing damaged
ACTION 1 − Check pressure switch tubing for
leaks. Replace any broken tubing.
LED#1−Off
LED#2
Slow Flash
LED#2−Slow
4.1.4
Pressure switch does not close due
to a low differential pressure across
the pressure switch.
ACTION 1 − Check the differential pressure
across the pressure switch. This pressure
should exceed the set point listed on the
switch.
ACTION 2 − Check for restricted inlet and exhaust vent. Remove all blockage.
ACTION 3 − Check for proper vent sizing and
run length. See installation instructions.
ACTION 4 − Check voltage to combustion air
blower.
4.1.5
Wrong pressure switch installed in
the unit, or pressure switch is out of
calibration.
ACTION 1 − Check that the proper pressure
switch is installed in the unit. Replace pressure
switch if necessary.
4.1.6
Miswiring of furnace or improper connections at pressure switch.
ACTION 1 − Check for correct wiring and loose
connections. Correct wiring and/or replace any
loose connections.
4.1.7
Pressure switch failure.
ACTION 1 − If all the above modes of failure have
been checked, the pressure switch may have
failed. Replace pressure switch and determine if
unit will operate.
Page 42
PROBLEM 5: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER
ENERGIZES, IGNITOR IS ENERGIZED. (CONT.)
Condition
Possible Cause
Corrective Action/Comments
5.1
5.1.1
Check that gas is being supplied to
the unit.
ACTION 1 − Check line pressure at the gas
valve. Pressure should not exceed 13" WC for
both natural and propane. Line pressure should
read a minimum 4.5" WC for natural and 8.0"WC
for propane.
5.1.2
Miswiring of gas valve or loose connections at multi−pin control amp
plugs or valve.
ACTION 1 − Check for correct wiring and loose
connections. Correct wiring and/or replace any
loose connections.
5.1.3
Malfunctioning gas valve or ignition
control.
ACTION 1 − Check that 24V is supplied to the
gas valve approximately 35 seconds after heat
demand is initiated.
ACTION 2 − Replace the valve if 24V is supplied
but valve does not open (check for excessive
gas line pressure before replacing gas valve).
ACTION 3 − Replace the control board if 24V is
not supplied to valve.
− Unit operates with a cooling and
continuous fan demand.
− Combustion air blower energizes
with Heating demand.
− Ignitor is energized but unit fails to
light.
LED#1−Alternating Slow Flash
LED#2−Alternating Slow Flash
PROBLEM 6: BURNERS LIGHT WITH A HEATING DEMAND BUT UNIT SHUTS DOWN
PREMATURELY
Condition
Possible Cause
Corrective Action/Comments
6.1
− Burners fire with a heating demand.
− Burners light but unit shuts off prior
to satisfying T−stat demand.
− Diagnostic lights flash the pressure
switch code.
6.1.1
Low pressure differential at the pressure switch.
ACTION 1 − Check for restricted vent inlet or exhaust. Remove all blockage.
ACTION 2: Check for proper vent sizing. See
installation instructions.
LED#1−Off
LED#2−Slow Flash
6.2
− Combustion air blower energizes
with a heating demand.
− Burners
B
light
li ht but
b t fail
f il to
t stay
t lit
lit.
− After 5 tries the control diagnostics
flash the watchguard burners failed to
ignite code.
LED#1−Alternating Slow Flash
LED#2−Alternating Slow Flash
6.2.1
Sensor or sense wire is improperly
installed.
ACTION 1 − Check that sensor is properly located (page 10) and that the sense wire is
properly attached to both the sensor and the
control.
6.2.2
Sensor or sense wire is broken.
ACTION 1 − Check for a broken sensor.
ACTION 2 − Test continuity across the sense
wire. If wire or sensor are damaged replace
the component.
6.2.3
Sensor or sensor wire is grounded to
the unit.
ACTION 1 − Check for resistance between the
sensor rod and the unit ground.
ACTION 2 − Check for resistance between the
sensor wire and the unit ground.
ACTION 3 − Correct any shorts found in circuit.
6.2.4
Control does not sense flame.
ACTION 1 − Check the microamp signal from
the burner flame. If the microamp signal is below 0.70 microamps, check the sense rod for
proper location or contamination.
ACTION 2 − Replace, clean, or relocate flame
sense rod. If rod is to be cleaned, use steel
wool or replace sensor. DO NOT CLEAN ROD
WITH SAND PAPER. SAND PAPER WILL
CONTRIBUTE TO THE CONTAMINATION
PROBLEM. NOTE: Do not attempt to bend
sense rod.
Page 43
PROBLEM 6: BURNERS LIGHT WITH HEATING DEMAND BUT UNIT SHUTS DOWN
PREMATURELY (CONT.)
Condition
6.3
− Combustion air blower energizes
with a heating demand.
− Burners light.
− Roll−out switch trips during the
heating demand.
− Diagnostic lights flash roll−out failure.
LED#1−On
LED#2−Slow Flash
6.4
− Combustion air blower energizes
with a heating demand.
− Burners light roughly and the unit
fails to stay lit.
− Diagnostic lights flash watchguard
flame failure.
LED#1−Alternating Slow Flash
LED#2−Alternating Slow Flash
Possible Cause
Corrective Action/Comments
6.3.1
Unit is firing above 100% of the
nameplate input.
ACTION 1 − Check that the manifold pressure
matches value listed on nameplate. See installation instructions for proper procedure.
ACTION 2 − Verify that the installed orifice size
match the size listed on the nameplate or installation instructions.
ACTION 3 − Check gas valve sensing hose to insure no leaks are present.
ACTION 4 − Check the input rate to verify rate
matches value listed on nameplate.
6.3.2
Gas orifices leak at the manifold connection.
ACTION 1 − Tighten orifice until leak is sealed.
NOTE: Be careful not to strip orifice threads. ACTION 2 − Check for gas leakage at the threaded
orifice connection. Use approved method for
leak detection (see unit instructions).
6.3.3
Insufficient flow through the heat exchanger caused by a sooted or restricted heat exchanger.
ACTION 1 − Check for sooting deposits or other
restrictions in the heat exchanger assembly.
Clean assembly as outlined in instruction manual.
ACTION 2 − For 80MGF gas furnaces, check for
proper combustion and flow. CO2 should measure between 6.0% and 8.0% for natural and
6.5% and 8.5% for L.P. CO should measure below .04% (400PPM) in an air−free sample of flue
gases.
6.3.4
Burners are not properly located in
the burner box.
ACTION 1 − Check that the burners are firing into
the center of the heat exchanger openings. Correct the location of the burners if necessary.
6.4.1
Recirculation of flue gases. This condition causes rough ignitions and operation. Problem is characterized by
nuisance flame failures.
ACTION 1 − Check for proper flow of exhaust
gases away from intake vent. Remove any obstacles in front of the intake and exhaust vent
which would cause recirculation.
ACTION 2 − Check for correct intake and exhaust vent installation. See instructions
6.4.2
Improper burner cross−overs
ACTION 1 − Remove burner and inspect the
cross−overs for burrs, or any restriction or if
crossover is warped. Remove restriction or replace burners.
Page 44
PROBLEM 6: BURNERS LIGHT WITH HEATING DEMAND BUT UNIT SHUTS DOWN
PREMATURELY (CONT.)
6.5
− Combustion air blower energizes
with a heating demand.
− Burners light.
− Diagnostic lights flash watch guard
flame failure.
− NOTE" Unit might go into 60 minute Watchguard mode depending on
intermittent nature of sensor signal.
6.5.1
Loose sensor wire connection
causes intermittent loss of flame signal.
ACTION 1 − Check that the sensor is properly located.
ACTION 2 − Check that the sense wire is properly attached to both the sensor and the control.
Pay extra attention to the pin connectors.
LED#1−Alternating Slow Flash
LED#2−Alternating Slow Flash
PROBLEM 7: CONTROL SIGNALS LOW FLAME SENSE DURING HEATING MODE
Condition
7.0
− Unit operates correctly but the
diagnostic lights flash low flame
sense code
code.
LED#1−Slow Flash
LED#2−Fast Flash
Possible Cause
Corrective Action/Comments
7.1.1
Sense rod is improperly located on
the burner.
ACTION 1 − Check the sense rod for proper location on the burner. Properly locate the sense rod
or replace if rod cannot be located correctly.
7.1.2
Sense rod is contaminated.
ACTION 1 − Check sense rod for contamination
or coated surface. Clean the sense rod with steel
wool or replace sensor. DO NOT USE SAND PAPER TO CLEAN ROD. SAND PAPER WILL
CONTRIBUTE TO THE CONTAMINATION
PROBLEM.
PROBLEM 8: INDOOR BLOWER FAILS TO OPERATE IN COOLING, HEATING, OR CONTINUOUS
FAN MODE
Condition
8.0
− Indoor blower fails to operate in
continuous fan, cooling, or heating
mode.
Possible Cause
Corrective Action/Comments
8.1.1
Miswiring of furnace or improper connections at control or indoor blower
motor.
ACTION 1− Correct wiring and/or replace any
loose connections. Check for correct wiring and
loose connections.
8.1.2
120V is not being supplied to the indoor air blower or blower motor failure.
ACTION 1 − Check for 120V at the various calls
for indoor blower by energizing "Y", "G", and "W"
individually on the low voltage terminal strip.
Note that when "W’ is energized, the blower is
delayed 45 seconds. If there is 120V to each motor tap but the blower does not operate, replace
the motor.
8.1.3
Defective control board
ACTION 1 − If there is not 120V when "Y", "G", or
"W" is energized, replace the control.
PROBLEM 9: RF STATIC DURING TIME FOR IGNITION
Condition
Possible Cause
Corrective Action/Comments
9.0
− AM radio interference
9.1.2
Ignitor operation
ACTION 1− Call Technical Support, Dallas
Page 45
SERVICE NOTES
Page 46