G24M
Service Literature
Corp. 9723-L12
Revised 07-2001
G24M SERIES UNITS
G24M series units are mid-efficiency gas furnaces manufactured with tubular steel heat exchangers formed of aluminized steel. G24M 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. Early model G24M
units use electronic (direct spark) ignition. Late model G24M
model units feature the Lennox SureLightT silicon-nitride
ignition system. The G24MX 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.
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.
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.
SPECIFICATIONS
Model No.
G24M2(X)-45
45,000 (13.2)
36,900 (10.8)
80.1%
75.4%
G24M2-60
G24M3(X)-60
G24M2-75
G24M3(X)-75
Input Btuh (kW)
60,000 (17.6)
75,000 (22.0)
Output Btuh (kW)
49,200 (14.4)
61,700 (18.1)
lA.F.U.E.
80.5%
80.5%
80.1%
80.0%
California Seasonal Efficiency
76.4%
75.9%
76.8%
76.8%
Flue size connection diameter — in. (mm) round
3 (76)
4 (102)
Temperature rise range — _F (_C)
30 - 60 (17 - 33)
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
1/2 (13)
in.
9x7
10 x 7
9x7
10 x 7
Blower wheel nominal
mm
229 x 178
254 x 178
229 x 178
254 x 178
diameter x width
Blower motor output — hp (W)
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
Nominal cooling
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
that can be added
Shipping weight — lbs. (kg) 1 package
130 (59)
135 (61)
Electrical characteristics
120 volts — 60 hertz — 1 phase (less than 12 amps) All models
b Optional Accessories (Must Be Ordered Extra) b
LPG/propane kit
LB-69845L (38K84)
Twinning Kit
96J69 — 5 lbs. (2 kg)
Up-Flow/Horizontal Filter and Filter Rack Kits
Single (32J02) Ten Pack (66K64)
}No. & size of filters - in. (mm)
(1) 16 x 20 x 1 (406 x 508 x 25)
Catalog No.
LB-69843A (32J01) — 3 lbs. (1 kg)
¡Down-flow
No. & Size of Filters — in. (mm)
Filter Kit
(2) 16 x 20 x 1 (406 x 508 x 25)
LB-79239A (67J91) — 10 lbs. (4 kg)
79J15 — 25 lbs. (11 kg)
LB-69957 (46J66) — 15 lbs. (8 kg)
Down-flow Combustible Floor Base
Sidewall Power Venting Kit
Hanging Bracket Kit
lAnnual 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.
¡Filters are not furnished with kit and must be ordered extra.
Page 1
ã 1998 Lennox Industries Inc.
Litho U.S.A.
SPECIFICATIONS
Model No.
G24M4(X)-75
Input Btuh (kW)
Output Btuh (kW)
RA.F.U.E.
California Seasonal Efficiency
Flue size connection diameter — in. (mm) round
Temperature rise range — EF (EC)
High static certified by A.G.A./C.G.A. — in wg.
(Pa)
75,000 (22.0)
61,700 (18.1)
80.0%
76.3%
80.1%
76.5%
4 (102)
80.0%
77.0%
35 - 65 (19 - 36)
.50 (125)
1/2 (13)
12 x 8
305 x 203
1/2 (373)
Tons
kW
Shipping weight — lbs. (kg) 1 package
Electrical characteristics
12 x 9
305 x 229
3/4 (560)
2, 2-1/2, 3, 3-1/2 or 4
3-1/2, 4, 5 or 6
7.0, 8.8, 10.6, 12.3 or 14.1
12.3, 14.1, 17.6 or 21.1
140 (64)
175 (79)
175 (79)
120 volts — 60 hertz — 1 phase (less than 12 amps) All models
Nominal cooling
that can be added
H
Optional Accessories (Must Be Ordered Extra)
LPG/propane kit
Twinning Kit
Up--Flow/Horizontal Filter and Filter Rack Kits
cNo. & size of filters - in. (mm)
Down-flow
Filter Kit
G24M4/5(X)-100
100,000 (29.3)
82,000 (24.0)
45 - 75 (25 - 42)
Gas Piping Size I.P.S. Natural or LPG/propane
in.
Blower wheel nominal
diameter x width
mm
Blower motor output — hp (W)
o
G24M3/4(X)-100
LB-69845L
(38K84)
Single (
) Ten Pack (
)
(1) 16 x 20 x 1 (406 x 508 x 25)
66K64
Catalog No.
No. & Size of Filters — in.
(mm)
Down-flow Combustible floor Base
Sidewall Power Venting Kit
Hanging Bracket Kit
LB-69845K
— 5 lbs. (2 kg)
Single
Ten Pack
(1) 20 x 20 x 1 (508 x 508 x 25)
(81J14)
96J69
32J02
H
(46J14)
LB-69843A
(32J01)
(66K65)
— 3 lbs. (1 kg)
(2) 16 x 20 x 1 (406 x 508 x 25)
LB-79239A
(67J91)
— 10 lbs. (4 kg)
LB-79239B
— 10 lbs. (4 kg)
— 25 lbs. (11 kg)
LB-69957
— 15 lbs. (8 kg)
(67J92)
79J15
(46J66)
R
c
o
Annual Fuel Utilization Efficiency based on U.S. DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating f or non-weatherized
furnaces.
Polyurethane frame type filter is furnished with kit.
Filters are not furnished with kit and must be ordered extra.
3DJH SPECIFICATIONS
Model No.
G24M3/4-120
G24M4/5-140
G24M4/5(X)-120
Input Btuh (kW)
140,000 (41.0)
120,000 (35.2)
Output Btuh (kW)
114,800 (33.6)
98,400 (28.8)
RA.F.U.E.
80.0%
80.0%
80.1%
California Seasonal Efficiency
Not Available
Not Available
75.5%
oFlue size connection diameter — in. (mm) round
4 (102)
5 (127)
Temperature rise range — EF (EC)
45 - 75 (25 - 42)
High static certified by A.G.A./C.G.A. — in wg. (Pa)
.50 (125)
.65 (162)
Gas Piping Size I.P.S. Natural or LPG/propane - in (mm)
1/2 (13)
in.
12 x 8
12 x 9
Blower wheel nominal
mm
diameter x width
305 x 203
305 x 229
Blower motor output — hp (W)
1/2 (373)
3/4 (560)
Tons
2,
2-1/2,
3,
3-1/2
or
4
3-1/2,
4, 5 or 6
Nominal cooling
kW
7.0, 8.8, 10.6, 12.3 or 14.1
that can be added
12.3, 14.1, 17.6 or 21.1
Shipping weight — lbs. (kg) 1 package
190 (86)
175 (79)
Electrical characteristics
120 volts — 60 hertz — 1 phase (less than 12 amps) All models
H
LPG/propane kit
Twinning Kit
Up--Flow/Horizontal Filter and Filter Rack Kits
cNo. and size of filters - in. (mm)
Catalog No.
wDown-flow
No. & Size in.
Filter Rack
mm
of Filters
Optional Accessories (Must Be Ordered Extra)
H
LB-69845K
— 5 lbs. (2 kg)
Single
Ten Pack
Single
Ten Pack
(1) 20 x 20 x 1 (508 x 508 x 25)
20 x 20 x 1 (508 x 508 x 25)
LB-69843A
— 3 lbs. (1)
(1 kg)
(2) 16 x 20 x 1
(2) 406 x 508 x 25
LB-79239C
LB-79239B
— 10 lbs. (4 kg)
— 12 lbs. (5 kg)
— 25 lbs. (11 kg)
LB-69957
— 15 lbs. (8 kg)
(81J14)
96J69
(46J14)
(66K65)
(58J93)
(66K66)
(32J01)
Down-flow Combustible Floor Base
Sidewall Power Venting Kit
Hanging Bracket Kit
(67J93)
(67J92)
79J15
(46J66)
R
c
o
w
Annual Fuel Utilization Efficiency based on U.S. DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating f or non-weatherized
furnaces.
Polyurethane frame type filter is furnished with kit.
2 in. x 5 in. (51 mm x127 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.
BLOWER DATA
G24M2-45, G24M2-60 AND G24M2-75 BLOW ER 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
3DJH BLOWER DATA
G24M3-60 AND G24M3-75 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
G24M4-75, G24M3/4-100 AND G24M3/4-120 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
3DJH BLOWER DATA
G24M4/5-100, G24M4/5-120 AND G24M4/5-140 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)
3DJH VENT ADAPTER
G24M
PARTS IDENTIFICATION
CABINET TOP
HEAT EXCHANGER
ASSEMBLY
FLUE BOX
COMBUSTION AIR
BLOWER
PRESSURE
SWITCH
G24M
CABINET
PRIMARY
LIMIT
FRONT LOUVERED
LOW PRESSURE SWITCH
PANEL
(Propane Only)
NOx
TURBULATOR
BURNER
ASSEMBLY
TRANSFORMER
SECONDARY
LIMITS
CABINET
BOTTOM
BLOWER ASSEMBLY
CONTROL
BOARD
DOOR INTERLOCK SWITCH
FIGURE 1
HEATING COMPONENTS (shown in horizontal position)
PRIMARY LIMIT
ROLLOUT SWITCH (2)
COMBUSTION AIR
PROVE SWITCH
ORIFICES
MANIFOLD
BURNERS
Left
Bottom
Front
Top
Right
HEAT EXCHANGER
GAS VALVE
COLLECTOR
FIGURE 2
Page 6
Back
COMBUSTION AIR BLOWER
G24M BURNER ASSEMBLY
(shown in upflow position with SureLight ignition system)
SURELIGHT
ROLLOUT
IGNITOR
SWITCHES
BURNER BOX
TOP
VEST PANEL
UPPER
BURNER
MOUNTING
RAIL
LOWER
BURNER
MOUNTING
RAIL
FLAME
BURNER
SENSOR
HEAT EXCHANGER
PRIMARY LIMIT
Top
Back
ORIFICE
Left
GAS VALVE
Right
Front
BURNER BOX
MANIFOLD
Bottom
FIGURE 3
G24M BLOWER DOOR COMPONENTS -- BLOWER ACCESS
To Access Blower:
4
1-- Turn off power to unit and disconnect L1
and L2 line voltage power.
2-- Disconnect thermostat wiring connections from furnace control board.
J135/
P135
3-- Remove screws (2) from blower panel.
4-- Disconnect J135 from P135 from limit
control.
5-- Disconnect J43 from blower motor.
J1/P1
6-- Remove blower panel and lift from unit.
5
Top
Right
Back
6
2
Left
1
3
FIGURE 4
Page 7
Front
Bottom
I-UNIT COMPONENTS (Figures 1, 2, 3)
DANGER
G24M unit components are shown in figure 1. The blower
controls, gas valve and burners can be accessed by reĆ
moving 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.
G24M units are factory equipped with bottom return air panels
in place. The panels are designed to be field removed as reĆ
quired for bottom air return. Indentations on side of units,
show where side return opening should be cut during installaĆ
tion.
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 reĆ
moved 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 secĆ
ondary.
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.
SURELIGHT IGNITOR
UPPER BURNER
MOUNTING RAIL
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- SureLight Ignition System (A3)
Late Model G24M Units
Late model G24M units are equipped with the Lennox
SureLight ignition system. The system consists of ignitor
(figure 5) and ignition control board (figure 6 with control
terminal designations in table 1). 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 termiĆ
nals rated at (4) four amps. See table 2 for troubleshootĆ
ing diagnostic codes. Table 3 and 4 show jack plug termiĆ
nal designations. Units equipped with the SureLight
board can be used with either electronic or electro-meĆ
chanical thermostats without modification. The SurĆ
eLight 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 temperaĆ
ture which will successfully light the burner, thus increasĆ
ing the life of the ignitor.
a-flame sensor
The flame sensor uses flame rectification to sense comĆ
bustion. During operation, flame is sensed by current
passed through the flame and sensing electrode. Figure 7
shows the gap between tip of the electrode and the burner
surface.
SURELIGHT IGNITOR BURNER ASSEMBLY
FLAME RETENTION RING
FIGURE 5
Page 8
ORIFICE
FLAME SENSOR
SURELIGHT CONTROL BOARD
LATE MODEL G24M UNITS
TABLE 1
SURELIGHT CONTROL TERMINAL DESIGNATIONS
ACB COOL
Blower - Cooling Speed (Line Volt)
ACB HEAT
Blower - Heating Speed (Line Volt)
PARK
Alternate Blower Speeds (Dead)
ACB LOW
Continuous Low Speed Blower
ACC
Accessory Terminal (Line Volt)
TX
120VAC Hot to Transformer
HOT
120VAC Hot Input
HTG ACC
Heat Only Accessory (Line Volt)
NEUTRALS
120VAC Neutrals
24VAC HOT
24VAC Hot from Transformer
24VAC RTN
24VAC Return from Transformer
FLAME SENSE Flame Sense Terminal
NORMAL FLAME SIGNAL > 0.7 MICROAMPS
LOW FLAME SIGNAL
< 0.7 MICROAMPS
MINIMUM FLAME SIGNAL < 0.15 MICROAMPS
FLAME SENSOR TO BURNER GAP
11/16 in. 18 mm
¦ 1/32 in. 0.79
mm
1/4 in. 7 mm
¦ 1/32 in. 0.79
mm
BURNER
3/16 in.
4.7 mm
FLAME
SIDE VIEWSENSOR
FIGURE 6
END VIEW
FIGURE 7
TABLE 2
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
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.
OFF
SLOW FLASH
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.
ALTERNATING SLOW
FLASH
ALTERNATING SLOW
FLASH
Watchguard - burners fail to ignite.
SLOW FLASH
OFF
Flame sensed without gas valve energized.
ON
SLOW FLASH
Rollout switch open. OR: 9 pin connector improperly attached.
ON
ON
OFF
ON
OFF
ON
Circuit board failure or control wired incorrectly.
FAST FLASH
SLOW FLASH
Main power polarity reversed. Switch line and neutral.
SLOW FLASH
FAST FLASH
Low flame signal. Measures below .7 microAmps. Replace flame sense rod.
ALTERNATING FAST
FLASH
ALTERNATING FAST
FLASH
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
Page 9
TABLE 3
not proven within 2-1/2 minutes, the control goes into
Watchguard-Pressure Switch mode for a 5-minute re-set
period.
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
NOTE - The G24M furnace contains electronic components that are polarity sensitive. Make sure that the
furnace is wired correctly and is properly grounded.
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. The ignitor stays energized for the first second of the 4-second trial. G24M
units with 63K89, 24L85 or 56L83: the ignitor stays energized the first second of the 4 second trial. G24M units with
board 97L48: ignitor stays energized during the 4-second
trial until flame is sensed. 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.
TABLE 4
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
c-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 8.
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.
NOTE—If 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.
b-Electronic Ignition
On a call for heat the SureLight control monitors the combustion air inducer prove switch. The control will not begin
the heating cycle if the prove switch is closed (by-passed).
Once the prove switch is determined to be open, the combustion air inducer is energized. When the differential in
the prove switch is great enough, the prove switch closes
and a 15-second pre-purge begins. If the prove switch is
Page 10
FAN-OFF TIME ADJUSTMENT
60sec.
90sec.
120sec.
180sec.
To adjust fan-off timing, flip dip switch to desired setting.
FIGURE 8
4-- Ram Control (A3)
Early Model G24M Units
Ignition Control
The ignition control is a direct spark ignition control
The furnace control combines burner ignition func-
module integral to the furnace control. See figure 9.
tions with blower control functions.
When there is a call for heat, the control delays ignition
Early
model
G24M
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 9. 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 conditions. The diagnostic LED lights
red (not flashing) to indicate control board failure. Table
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 the spark ignitor 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 21.
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
7 shows how to interpret the other LED modes.
will attempt ignition up to three times. The control can
Pre-Purge
On a call for heat, the combustion air blower begins
operating. If the combustion air prove switch closes,
be manually reset before the end of 60 minutes by momentarily turning off power to the unit.
DANGER
the combustion air blower continues to operate for 45
seconds (pre-purge) before allowing ignition. Prepurge allows the heat exchanger to be cleared of com-
Shock hazard.
bustion products and to introduce fresh air for com-
Spark related components contain high voltage.
Disconnect power before servicing. Control is not
field repairable. If control is inoperable, simply replace entire control.
bustion. If the combustion air prove switch does not
close, the combustion air blower continues to run indefinitely (until the prove switch closes).
Can cause injury or death. Unsafe operation will
result if repair is attempted.
Post-Purge
After a demand, the combustion air blower continues
to operate for 5 seconds (post-purge) before stopping.
Post-purge allows the heat exchanger to be cleared of
combustion products.
Page 11
EARLY MODEL G24M FURNACE CONTROL (A3)
SPARK OUTPUT
24VAC VOLT
TERMINAL
CONNECTIONS
LINE VOLTAGE
TERMINAL
CONNECTIONS
PLUG P20
See Table 6 for
Terminal
Functions
FAN-OFF TIMING
SWITCHES
THERMOSTAT
CONNECTIONS
DIAGNOSTIC
LED
FIGURE 9
TABLE 5
When flame is sensed, the indoor blower starts after a
Furnace Control A3 Limit Response During Operation
Response
45 second delay. Gas valve remains open and blower
Condition
Combustion
Air
Blower
Gas
Valve
Supply
Air
Blower
continues to run until demand stops, flame sensor
Diagnostic
stat demand, the gas valve closes and the diagnostic
Loss of Flame
Sensed Before
On Delay
LED registers the error condition (table 5).
On
End of 45 second Blower
senses loss of flame, a limit opens or the prove switch
opens. If any of these events occur during a thermo-
LED
(Spark
On
Starts
On
Fast Flash
Blower Control and Timings
Within 0.8
(3 or Fewer
DANGER
seconds)
Trials
for Ignition)
Electrical Shock Hazard.
Loss of Flame
Sensed After
Off Then
45 second
On With
Blower On
On
Spark
Delay (3 or
After Pre-
Fewer Trials
Purge
This control contains field adjustable switches
and also contains line voltage. Make sure power
On
is disconnected before making any field adjust-
Fast Flash
ments or performing any service procedure.
for Ignition)
NOTE—If fan “off” time is set too low, residual heat
Loss of Flame
Sensed (More
Than 3 Trials
Off
Off
Off
in heat exchanger may cause primary limit S10 to
2 Flashes
trip resulting in frequent cycling of blower. If this
for Ignition)
occurs, adjust blower to longer time setting.
Flame Sensed
Without
On
Off
On
5 Flashes
Demand
the supply air blower starts) is fixed at 45 seconds and
Primary or
Secondary
On
Off
On
4 Flashes
Limit Open
Rollout Switch
Open
Air Prove
cannot be adjusted.
Fan “OFF” timings (time that the blower operates after
On
Off
On
4 Flashes
a heating or cooling demand has been satisfied) are determined by the arrangement of switches on the fur-
Combustion
Switch Open
Fan “ON” timing (time that the burners operate before
On
Off
On
3 Flashes
nace control board. See figure 9. To adjust fan “off ”
timings, gently reposition the switches to a new timing
Page 12
TABLE 7
position. Figure 10 shows the various fan “off” timings
and how switches should be positioned. Unit is shipped
with a factory fan “off” setting of 180 seconds. Fan “off”
LED State
time will affect comfort and efficiency and is adjustable
Steady On
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
Slow Flash
Fast Flash
is changed from ON to AUTO and heating/cooling de-
Furnace Control A3 Diagnostic LED
Meaning
Remedy
Control Failure
Replace Control
Normal Operation
- - - -
and No Call For Heat
Normal Operation
- - - -
with Call For Heat
Failed to Sense or Sustain
mand is not present, the blower stops immediately).
Flame. Check Gas Valve,
Two
TABLE 6
Flashes
Control Lockout
Burners, Spark Electrode
and Wire, Flame Sensor.
FURNACE CONTROL A3 TERMINAL DESIGNATIONS
Terminal
Type
Function
24VAC HOT
1/4” Spade
24VAC In From Transformer
GND
1/4” Spade
To Cabinet Ground
Y
Screw Strip
Cooling Demand
G
Screw Strip
Blower Demand
Replace Control If All OK.
Failed to Prove CombusThree
Flashes
tion Blower Operation or
Pressure Switch Open
Blocked Vent. Repair or
Replace as Necessary.
Check Primary Limit,
Rollout Switches and Sec-
R
Screw Strip
24VAC to Thermostat
Four
W
Screw Strip
Heating Demand
Flashes
C
Screw Strip
24VAC Common
120VAC HOT
1/4” Spade
Line Voltage In
ondary Limits. Find source
Open Limit
of Overtemperature. If all
OK, Reset or Replace Limits as Necessary.
Five
Flame Sensed and Gas
Check Gas Valve. If OK,
Flashes
Valve Not Energized.
Check Flame Sensor.
120VAC RTN
1/4” Spade
Line Voltage Neutral
120VAC TX
1/4” Spade
Line Voltage Out To Transformer
CMB
J20/P20 Pin 1
Switched 120VAC to
Combustion Air Blower
B--Blower Motors and Capacitors
CMB RTN
J20/P20 Pin 2
120VAC Common
Combustion Air Blower
All G24M units use direct drive blower motors. All mo-
ACB HEAT
1/4” Spade
Switched 120VAC to
Blower Heating Tap
ACB LOW
1/4” Spade
120VAC Output to Supply Air
Blower for Continuous Operation During No Demand
ACB COOL
1/4” Spade
Switched 120VAC to Blower
Cooling Tap
VLV HOT
tors used are 120V permanent split capacitor motors to
ensure maximum efficiency. See table8 for ratings.
TABLE 8
G24M BLOWER RATINGS 120V 1PH
BLOWER MOTOR
HP
CAP
G24MQ2
1/4
5MFD 370V
5MFD 370V
J20/P20 Pin 13
24VAC to Gas Valve
G24MQ3
1/3
J20/P20 Pin 9
24VAC Common From
Gas Valve
G24MQ3/4
1/2
7.5MFD 370V
1/2
7.5MFD 370V
J20/P20
Pin 10
24VAC In From Pressure Switch
Switch Open: Prohibits Ignition
Switch Closed: Allows Ignition
G24MQ4
G24MQ4/5
3/4
40MFD 370V
G24MQ5/6
3/4
40MFD 370V
HIL IN
J20/P20
Pin 11
24VAC In From Limits
Limit Open: Closes Gas Valve
Limits Closed: Allows Ignition
HIL OUT
J20/P20
Pin 14
24VAC to Limit Train
and Pressure Switch
RO OUT
J20/P20 Pin 7
24VAC Out To Rollout Switches
VLV RTN
PSW IN
SECONDARY
LIMITS (S21)
RO IN
J20/P20 Pin 15
24VAC In From Rollout Switches
SPARK
ELECTRODE
Male Spark
Plug Type
High Voltage Out To
Spark Electrode
FS
J20/P20 Pin 12
Flame Microamp Sensing
FAN-OFF TIME ADJU
SUPPLY AIR BLOWER
AND SECONDARY LIMITS
Top
Back
Left
Right
Front
STMENT SWITCHES
Bottom
LOCATED ON FURNACE CONTROL (A3)
Fan-Off Timings
Switch
Timing
Seconds
1
2
Off
Off
90
Off
On
120
On
Off
180
On
On
240
BLOWER
MOTOR
FIGURE 10
MOTOR
Diagnostic LED
CAPACITOR
The furnace control is equipped with a diagnostic LED
To Remove Blower From Unit: Remove Bolts and
used for troubleshooting the unit and the control. LED
Wiring Jackplugs. Then Slide Out Front of Unit.
FIGURE 11
functions are shown in table 7.
Page 13
C--Combustion Air Blower (B6)
E--Primary Limit Control (S10)
All G24M units use a combustion air blower to move
LIMIT CONTROL FOR
G24M SERIES UNITS
air through the burners and heat exchanger during
heating operation. Some early model G24M units are
THIS TYPE AUTO-RESET LIMIT
IS USED FOR THE PRIMARY LIMIT (S10) AND
equipped with a blower that uses a PSC (Permanent
RIGHT SECONDARY LIMIT (S21)
(see FIGURE 11)
Split Capacitor) 120VAC motor. PSC motors use run
capacitors. Other early and late model G24M units are
equipped with a blower that uses a shaded pole 120V
FIGURE 13
motor. The motor operates during all heating opera-
The primary limit (S10) on G24M units is located in the
tion and is controlled by furnace control A3. For G24M
middle of the heating vestibule panel. When excess heat
units equipped with the Ram ignition system, the
is sensed in the heat exchanger, the limit will open. If the
blower will operate for 45 seconds before burner igni-
limit is tripped, the furnace control energizes the supply
tion (pre-purge) and for 5 seconds after the gas valve
air blower and closes the gas valve. The limit automati-
closes (post-purge). For G24M units equipped with the
cally resets when unit temperature returns to normal.
SureLight ignition system, the blower will operate for
The switch is factory set and cannot be adjusted. The
15 seconds before burner ignition (pre purge) and for 5
switch may have different setpoints for each unit model
seconds after the the gas valve closes (post purge).
number. However, the setpoint will be printed on the
A pressure switch connected to the combustion air
side of the limit.
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 negative. 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.
F--Secondary Limit Controls (S21)
The secondary limit (S21) on G24M units is located in the
blower compartment in the back side of the blower
housing.
When excess heat is sensed in the 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
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
set and cannot be adjusted. Two limits are supplied in
each furnace and each limit is a different style (figures
13 and 14). The setpoint will be printed on the side of
the limit. If stick limit (figure 14) suffers from nuisance
trips anf the furnace is in the horizontal position, replace with limit kit no. 50L98.
SECONDARY LIMIT CONTROL (S21)
with the ignition control A3. When S47 senses rollout,
FOR G24M SERIES UNITS
the ignition control immediately stops ignition and
control will be disabled. Rollout can be caused by a
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.
LIMIT (S21) (see FIGURE 11)
INSULATING COVER (s)
FIGURE 14
ROLLOUT SWITCH (S47)
MANUAL
RESET BUTTON
USED FOR THE LEFT SECONDARY
LIMIT
blocked flue or lack of combustion air. The switch is
THIS TYPE AUTO-RESET LIMIT IS
SPADE CONNECTORS
out is detected, the gas valve will close and ignition
LIMIT
INSULATING COVER
closes the gas valve. If unit is running and flame roll-
G--Spark Electrode and Flame Sensor
Early Model G24M Units
Figure 15 shows the arrangement of flame sensor,
spark electrode and burners. The ignition control uses
direct spark to ignite the rightmost burner and the
FIGURE 12
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 16 shows the gap between tip of the electrodes
and the burner surface.
Page 14
Top
TYPICAL BURNER/ELECTRODE ORIENTATION
view looking at flame end of burners
1/8”(+1/64”)
UPPER BURNER
BURNER
MOUNTING RAIL
GROUND
SPARK ELECTRODE
MANIFOLD
Right
ORIFICE
Bottom
FLAME SENSOR
LOWER BURNER
FLAME RETENTION RING
Left
(SOME UNITS MAY HAVE
MOUNTING RAIL
SENSOR LOCATED IN
MIDDLE OF BURNER)
FIGURE 15
TYPICAL ACCESS TO REGULATOR
SPARK ELECTRODE TO BURNER GAP
FOR ADJUSTMENT AND L.P. CHANGEOVER
(Honeywell VR8205 series gas valve shown)
p
p
11/16 in. 18 mm
1/4 in. 7 mm
1/32 in. 0.79
1/32 in. 0.79
mm
BURNER
mm
287/(7
3/16 in.
35(6685(
4.7 mm
7$3
,1/(7
21
35(6685(
7$3
2))
FLAME
SIDE VIEWSENSOR
*$6 9$/9( 6+2:1 ,1 2)) 326,7,21
END VIEW
&$3 6&5(:
%ODFN
FIGURE 16
H--Gas Valve
The G24M uses a gas
635,1*
35(6685(
valve manufactured by Honey-
7DSHUHG (QG
5(*8/$725
$'-867,1* 6&5(:
'RZQ
5HG
:KLWH
well (figure 17) or White Rodgers (figure 18). The valve
is internally redundant to assure safety shut--off. If the
,1/(7
gas valve must be replaced, the same type valve must
35(6685(
7$3
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
*$6 ,1/(7
regulator adjustment screw is located on the valve. Refer
to figure 17 or 18 for location of valve features.
FIGURE 17
An LPG changeover kit is available from Lennox. The kit
includes burner orifices and a regulator conversion kit.
WHITE RODGERS
GAS VALVE
I--Combustion Air Blower Prove
(Pressure) Switch (S64)
36E GAS VALVE
KNOB SHOWN
REGULATOR
COVER SCREW
IN OFF POSITION
G24M 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
GAS INLET
means of a flexible silicone hose. It monitors air pressure in the combustion air blower housing.
35(6685(
35(6685(
7$3
7$3
FIGURE 18
Page 15
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 opera-
III--START-UP
A--Preliminary and Seasonal Checks
1 -- Inspect electrical wiring, both field and factory
tion if the combustion air blower is not operating.
installed for loose connections. Tighten as required.
2 -- Check voltage at disconnect switch. Voltage must
PROVE SWITCH
COMBUSTION AIR BLOWER
be within range listed on the nameplate. If not,
PROVE SWITCH
Normally Open
consult the power company and have voltage
Closes on Negative Pressure
condition corrected before starting unit.
B--Heating Start-Up
1 -- Set thermostat to OFF position. Close manual
knob on gas valve.
2 -- Wait 5 minutes.
3 -- Open manual knob on gas valve, replace burner
Sensing Tube
Attaches to Top
access door and turn on unit electrical supply.
Side Of Blower
Back
WARNING
Top
Right
Shock and burn hazard.
PROVE
SWITCH
G24M units are equipped with either a direct spark
Left
Front
or hot surface ignition system. Do not attempt to
Bottom
light manually.
FIGURE 19
4 -- Set fan switch to AUTO or ON and move system
On start-up, the switch senses that the combustion air
selection switch to HEAT. Adjust thermostat to a
blower is operating. It closes a circuit to the furnace
setting above room temperature.
control when pressure inside the combustion air
5 -- If unit does not light the first time, the SureLight
blower increases above switch setting (negative) w.c.
control will attempt four more ignitions, the Ram
The pressure sensed by the switch is relative to atmo-
control will attempt two more ignitions before
spheric pressure. If the flue becomes obstructed dur-
locking out.
ing operation, the switch senses a loss of negative
6 -- If lockout occurs, repeat steps 1, 2, 3 and 4.
pressure (pressure becomes more equal with atmo-
C--Safety or Emergency Shutdown
spheric pressure) and opens the circuit to the furnace
control and gas valve. The switch trip pressure is dif-
Turn off unit power. Close manual and main gas valves.
IMPORTANT
ferent 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
In case emergency shutdown is required, turn off
a safety shut-down control in the furnace and must not
the main shut-off valve and disconnect the main
be bypassed for any reason.
power to unit. These controls should be properly
II--PLACEMENT AND INSTALLATION
labeled by the installer.
Make sure unit is installed in accordance with installa-
D--Extended Period Shutdown
tion instructions and applicable codes.
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.
Page 16
IV--HEATING SYSTEM SERVICE CHECKS
underfire. High pressure can result in permanent dam-
A--A.G.A./C.G.A. Certification
age to gas valve or overfire. For natural gas units, op-
All units are A.G.A. design certified without modifica-
tween 5.0” W.C. and 13.0” W.C. For L.P. gas units,
tions. Refer to the G24M Operation and Installation
operating pressure at unit gas connection must be be-
Instruction Manual for Information.
tween 10.0” W.C. and 13.0” W.C.
B--Gas Piping
On multiple unit installations, each unit should be
Gas supply piping should not allow more than 0.5”W.C.
checked separately, with and without other units oper-
drop in pressure between gas meter and unit. Supply
ating. Supply pressure must fall within range listed in
gas pipe must not be smaller than unit gas connection.
previous paragraph.
Compounds
used
on
gas
piping
erating pressure at unit gas connection must be be-
threaded
joints
E--Check Manifold Pressure
should be resistant to action of liquefied petroleum
After line pressure has been checked and adjusted,
gases.
check manifold pressure. Move pressure gauge to out-
C--Testing Gas Piping
let pressure tap located on unit gas valve (GV1).
When pressure testing gas lines, the gas valve must be
proper regulator adjustment. Manifold pressure for the
disconnected and isolated. Gas valves can be dam-
G24M can be measured at any time the gas valve is
aged if subjected to more than 0.5psig (14” W.C.). See
open and is supplying gas to the unit. Normal manifold
figure 20. If the pressure is equal to or less than 0.5psig
pressure for natural gas units is 3.5 in. w.c. For LP/pro-
(14”W.C.), use the manual shut--off valve before pres-
pane gas the correct manifold pressure is 9.5 in. w.c.
Checks of manifold pressure are made as verification of
sure testing to isolate furnace from gas supply.
IMPORTANT
GAS PIPING TEST PROCEDURE
MANUAL MAIN SHUT--OFF VALVE
For safety, connect a shut-off valve between the
WILL NOT HOLD TEST PRESSURE
manometer and the gas tap to permit shut off of
IN EXCESS OF 0.5 PSIG (14”W.C.)
gas pressure to the manometer.
TABLE 9
GAS VALVE REGULATION
Unit (Fuel)
Operating Pressure (outlet) in. W.C.
Natural
L.P.
CAP
3.5 +0 --0.3
9.5 + 0.5
GAS VALVE
The gas valve is factory set and should not require adFIELD PROVIDED
justment. All gas valves are factory regulated. See
LINE PRESSURE TAP
table 9.
FIGURE 20
Manifold Adjustment Procedure:
When checking piping connections for gas leaks, use
1 -- Connect a test gauge to outlet pressure tap on gas
preferred means. Kitchen detergents can cause harmful
valve. Start unit and allow 5 minutes for unit to
corrosion on various metals used in gas piping. Use of a
reach steady state.
specialty Gas Leak Detector is strongly recommended. It
is
available
through
Lennox
under
part
number
2 -- While waiting for the unit to stabilize, notice the
flame. Flame should be stable and should not lift
31B2001. See Corp. 8411--L10, for further details.
from burner. Natural gas should burn blue. L.P. gas
Do not use matches, candles, flame or any other
source of ignition to check for gas leaks.
should burn mostly blue with some orange streaks.
3 -- After allowing unit to stabilize for 5 minutes, re-
D--Testing Gas Supply Pressure
cord manifold pressure and compare to values
When testing supply gas pressure, connect test gauge
given in table 9.
to inlet pressure tap (field provided). See figure 20.
NOTE--Shut unit off and remove manometer as
Check gas line pressure with unit firing at maximum
soon as an accurate reading has been obtained.
rate. Low pressure may result in erratic operation or
Take care to replace pressure tap plug.
Page 17
F- Proper Gas Flow
TABLE 11
Furnace should operate at least 5 minutes before checkĆ
ing gas flow. Determine time in seconds for two revoluĆ
tions of gas through the meter. (Two revolutions assures
a more accurate time.) Divide by two and compare to time
in table 10 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.
TABLE 10
GAS METER CLOCKING CHART
Seconds for One Revolution
Natural
LP
G24M
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
26
52
64
128
Natural-1000 btu/cu ft
ALTITUDE
feet (m)
GAS FUEL
MANIFOLD
PRESSURE
in. W.C. (kPa)
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)
Natural
3.2 (0.80)
Propane/LP
8.6 (2.14)
0 - 4500
(0 - 1372)
6500 - 7500
(1372 - 2286)
TABLE 12
Pressure Switch Part Number
No Change
No Change
88J8001
18L2401
18L2401
No Change
Unit Model
G24M-45
G24M-60
G24M-75
G24M-100
G24M-120
G24M-140
IMPORTANT
LP-2500 btu/cu ft
For safety, shut unit off and remove manometer as
soon as an accurate reading has been obtained.
Take care to replace pressure tap plug.
NOTE- To obtain accurate reading, shut off all other
gas appliances connected to meter.
G-High Altitude Derate
H-Flame Signal
NOTE-In Canada, certification for installation at altiĆ
tudes over 4500 ft. (1372m) above sea level is the jurisĆ
diction of the local authorities.
G24M-1 through -9 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 oriĆ
fice change is required.
NOTE-This is the only permissible field derate for this
appliance.
G24M-10 and -11 Models
Table 11 shows manifold pressure settings for installations
at different altitudes. Refer to table 12 for pressure switch
replacement for models at elevations of 4500 feet (1372m)
and greater.
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 elecĆ
trode during unit operation. Current passes from the senĆ
sor through the flame to ground to complete a safety cirĆ
cuit.
To Measure Flame Signal:
1 - Place meter in series between furnace control and
sensor wire. Connect the positive (+) lead of meter to
the ignition control sensor connection and the negaĆ
tive (-) lead of the meter to the sensor wire. See figure
21.
2 - Set thermostat for a heating demand and check flame
signal with unit operating. For G24M series with a RAM
control, a reading of 1 to 5 microamps DC should occur.
The furnace control must see at least 1.0 microamps in
order to keep the gas valve energized. G24M units with
the SureLight control should read 0.7 microamps or
more.
Page 18
FLAME SIGNAL TEST
RAM CONTROL
SHOWN
D.C. MICROAMP
METER
FLAME
SENSOR
IGNITION
CONĆ
TROL
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 raĆ
diant heat from the heat exchanger.
2 - Set thermostat to highest setting.
SENSE"
TERMINAL
SENSOR
WIRE
FIGURE 21
Flame signal from the Ram control may rise above 5 microĆ
amps 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.
3 - After plenum thermometers have reached their highĆ
est 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, inĆ
crease 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 22.
2 - Punch a 1/4" diameter hole STATIC PRESSURE
TEST
in supply and return air pleĆ
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.
2 - Generally, blower operation is set at thermostat subĆ
base fan switch. With fan switch in ON position, blower
operates continuously on low speed. With fan switch in
AUTO position, blower cycles with demand or runs conĆ
tinuously while heating or cooling circuit cycles.
3 - In all cases, blower and entire unit will be off when the
system switch is in OFF position.
B-Temperature Rise
set for unit operation within the range of AIR TEMP. RISE
°F" listed in the unit rating plate.
To Measure Temperature Rise:
Temperature rise for G24M units depends on unit input,
blower speed, blower horsepower and static pressure as
marked on the unit rating plate. The blower speed must be
nums. Insert manometer
MANOMETER
hose flush with inside edge
of hole or insulation. Seal
around the hose with perĆ
G24M UNIT
magum. Connect the zero
FIGURE 22
end of the manometer to the
discharge (supply) side of the system. On ducted sysĆ
tems, connect the other end of manometer to the reĆ
turn duct as above. For systems with non-ducted reĆ
turns, 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 blowĆ
er 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.
Page 19
D-Blower Speed Taps Leadless Motors
Blower speed tap selection is accomplished by changing the
taps at the blower motor harness connector. Disconnect harĆ
ness connector from motor to expose speed selectors.
Blower speed selections are listed in table 13.
To Change Blower Speed:
1 - Turn off electric power to furnace.
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 conĆ
nected 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 14 for blower motor tap colĆ
ors for each speed.
TABLE 13
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 (refer to
unit wiring diagram).
5 - Depress harness connector tab to release wire termiĆ
nal. Select connector location for new speed (refer to
unit wiring diagram). Insert wire terminal until it is seĆ
curely in place. See figure 23.
6 - Replace harness connector to motor.
TABLE 14
BLOWER SPEED TAP SELECĆ
TION
HARNESS
LEADLESS MOTORS CONNECTOR
VI-MAINTENANCE
DEPRESS TAB TO RELEASE
WIRE TERMINAL. SELECT
CONNECTOR
LOCATION
FOR NEW SPEED (REFER TO
UNIT WIRING DIAGRAM). INĆ
SERT WIRE UNTIL IT IS SEĆ
CURELY IN PLACE.
At the beginning of each heating season, the system
should be checked as follows:
A-Filters
A filter must be used in order to ensure long life and proper
operation. The filter is located in the return air duct or return
air register. Filters must be cleaned or replaced when dirty
to assure proper unit operation.
MOTOR
FIGURE 23
B-Heat Exchanger and Burners
E-Blower Speed Taps Leaded Motors
Blower speed tap changes are made on the SureLight
control board. See figure 6. Unused taps must be secured
on dummy terminals "PARK M1" and or "PARK M2" on the
NOTE-Use papers or protective covering in front of furĆ
nace while cleaning furnace.
Due to dimples designed in the heatexchanger, cleaning is
not recommended. Removal is for inspection only.
Page 20
To clean burners:
CAUTION
1 -- Turn off both electrical and gas power supplies to
furnace.
Potential for gas leaks, fire or explosion.
2 -- Disconnect gas supply piping and remove gas
Some soaps used for leak detection are corrosive
manifold.
to certain metals.
3 --
Disconnect ignitor and flame sensor leads.
4 --
Remove burner tray and burners.
5 --
Clean burner retention ring with wire brush.
6 --
Use test tube brush to clean inside of each burner.
7 --
Replace burners and burner tray, making sure
Can cause damage to piping resulting in gas
leaks, fire or explosion.
burners are properly seated in slots on tray and ori-
C--Supply Air Blower
1 -- Check and clean blower wheel.
2 -- Motors used on the Lennox G24M series units
are permanently lubricated and need no further
fice in manifold.
8 --
Reinstall burner box and gas supply piping. Reconnect ignitor and flame sense leads.
9 --
Carefully check all piping connections (factory and
field) for gas leaks. Use a leak detecting solution or
other preferred means.
10 -- Restore electrical power and gas supply. Follow
lighting instructions on front of unit.
Carefully clean piping thor-
oughly after leak detection has been completed.
lubrication.
D--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.
E--Electrical
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 24
Page 21
VII--WIRING, OPERATION SEQUENCE
&TROUBLESHOOTING
A--Field Wiring, Thermostat Connections
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,17(5/2&.
6:,7&+
),*85( G24M and CONDENSING UNIT
THERMOSTAT DESIGNATIONS
(Refer to specific thermostat and outdoor unit.)
Thermostat
Y
G24M
Furnace
COOLING
Y
Condensing Unit
COMPRESSOR
HS UNIT
COMPRESSOR
INDOOR BLOWER
G
G
HEAT
W
W
POWER
R
R
COMMON
COMMON
C
C
),*85( 3DJH HS UNIT
COMMON
*1'
B--Early Model G24M Series With Ram Ignition Control
limits (S21) are closed, the furnace control begins
1 -- When disconnect is closed, 120V is routed through
a 45 second time-delay (pre-purge).
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
6 -- At the end of the pre-purge cycle, the furnace control simultaneously opens the gas valve and sends
A3 and T1 to receive voltage.
high voltage to the spark electrode.
2 -- T1 supplies 24VAC to terminal “24VAC” on A3. In
turn, terminal “R” of A3 supplies 24VAC to termi-
7 -- When flame is sensed, the furnace control begins
a 45 second delay before energizing the indoor
nal “RC” of the indoor thermostat (not shown).
blower.
3 -- When there is a call for heat, W1 of the thermostat
energizes W of the furnace control with 24VAC.
8 -- When heat demand is satisfied, W1 of the thermostat de-energizes W of the furnace control and the
4 -- CMB BLWR of the blower control energizes the
furnace control immediately de-energizes the gas
combustion air blower (B6). When the combustion
valve. The combustion air blower runs for 5 se-
air blower nears full speed, combustion air prove
conds (post-purge) before being de-energized.
switch (S18) closes.
Also, the indoor blower runs for a designated peri-
5 -- When S18 closes, assuming the flame rollout
switch (S47), primary limit (S10) and secondary
3DJH od (90--240 seconds) as set by switches on furnace
control.
C--Ram Ignition Control Troubleshooting Guide
RAM CONTROL
HEATING TROUBLE SHOOTING SEQUENCE
NORMAL HEATING MODE
ABNORMAL HEATING MODE
LED: SLOW FLASH RATE
THERMOSTAT CALLS FOR HEAT
LED: FAST FLASH RATE
FLAME OFF?
NO
CONTROL SELF--CHECK OKAY?
NO
HI LIMIT SWITCH CLOSED?
NO
PRESSURE SWITCH OPEN?
NO
YES
YES
YES
YES
COMBUSTION AIR BLOWER ON?
PRESSURE 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
CHECK TO SEE IF MAIN VALVE IS OFF.
SEQUENCE HOLDS UNTIL HI LIMIT CLOSES.
LED: 4 flashes.
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.
MAIN VALVE AND SPARK OFF.
YES
SYSTEM FAN ON.
(Fixed 45--second delay)
FLAME SENSE OKAY?
NO
NO
YES
START IGNITION SPARK (IN 0.8 SEC. MAXIMUM).
HAS FLAME BEEN DETECTED WITHIN 7 SEC.?
FLAME CONTINUOUSLY CHECKED?
ROLLOUT SWITCHES CLOSED
YES
HI LIMIT SWITCH CLOSED?
YES
PRESSURE SWITCH CLOSED?
YES
NO
LOCKOUT. MAIN VALVE OFF.
COMBUSTION AND SYSTEM FANS ON.
RESET OR REPLACE ROLLOUT SWITCH.
LED: 4 flashes.
NO
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
COMB. AIR BLOWER OFF (5 sec. delay)
COMBUSTION FAN ON. SYSTEM FAN OFF.
(AFTER DELAY TO OFF INTERVAL COMPLETED.)
YES
FAN OFF (After selected 90, 120,
180, or 240 delay)?
NO
NO
YES
LED: Fast flash rate.
3DJH YES
RAM CONTROL
COOLING TROUBLE SHOOTING SEQUENCE
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
COMPLETING SELECTED DELAY INTERVAL
(At dip switches).
MANUAL FAN TROUBLESHOOTING SEQUENCE
LED: Slow flash rate.
REMAINS UNCHANGED THROUGHOUT SEQUENCE.
MANUAL FAN SELECTION MADE AT THERMOSTAT.
CONTROL ENERGIZES SYSTEM FAN AT CONTINUOUS
SPEED. ACC TERMINAL ENERGIZED.
THERMOSTAT CALLS FOR HEAT.
YES
NO
SYSTEM FAN SWITCHES TO HEATING SPEED AFTER
SELECTED DELAY. ACC TERM. REMAINS ENERGIZED.
THERMOSTAT CALLS FOR COOLING.
YES
SYSTEM FAN SWITCHED TO COOLING
SPEED. ACC TERMINAL REMAINS ENERGIZED.
NO
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 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.
3DJH D-Late Model G24M Series With SureLight Ignition Control
TYPICAL G24M DIAGRAM
(-11 MODEL SHOWN)
123-
4-
When there is a call for heat, W1 of the thermostat energizes W of the furnace control with 24VAC.
S10 primary limit switch and S47 rollout switch are closed.
Call for heat can continue.
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.
SureLight control energizes ignitor. A 20-second warm-up
period begins.
5-
678-
Page 26
Gas valve opens for a 4-second trial for ignition. Ignitor
stays energized the first second of trial. (Board 97L48 only:
ignitor energized during trial or until flame is sensed.
Flame is sensed, gas valve remains open for the heat call.
After 45-second delay, SureLight control energizes indoor
blower B3.
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.
SURELIGHT CONTROL HEATING
SEQUENCE OF OPERATION
NORMAL HEATING MODE
ABNORMAL HEATING MODE
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
POWER ON
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?
NO
SIGNAL IMPROPER
GROUND AT LED.
SIGNAL HOLDS
UNTIL UNIT IS
PROPERLY
GROUNDED.
NO
IS VOLTAGE
ABOVE 75 VOLTS?
YES
IS THERE
PROPER GROUND?
YES
NO
BURNER OFF?
(CONTINUOUS FLAME CHECK)
POLARITY REVERSED.
LED #1 ---- FAST FLASH
LED #2 ---- SLOW FLASH
LOW VOLTAGE SIGNAL AT LED HOLDS
UNTIL VOLTAGE RISES ABOVE 75 VOLTS.
NO
ROLLOUT SWITCH CLOSED?
YES
NO
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.
YES
NORMAL OPERATION:
GAS VALVE OFF. COMBUSTION AIR BLOWER ON.
INDOOR BLOWER ON HEATING SPEED.
LED #1 ---- SLOW FLASH
LED #2 ---- OFF
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
HAS COMBUSTION AIR PRESSURE
SWITCH CLOSED IN 2.5 MINUTES?
NO
YES
15-SECOND COMBUSTION AIR BLOWER PREPURGE
INITIATED BY CLOSED PRESSURE SWITCH.
YES
CONTINUED NEXT PAGE
3DJH 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
4-SECOND TRIAL FOR IGNITION. GAS VALVE OPENS.
IGNITOR ENERGIZED FOR 1 SECOND AFTER VALVE
OPENS. NO FLAME SENSED DURING THIS PERIOD.
BOARD 97L48: IGNITOR ENERGIZED DURING TRIAL OR
UNTIL FLAME SENSED.
YES
FLAME STABILIZATION PERIOD.
4 SECONDS
NO
NO
LEDS SIGNAL
ALTERNATING
FAST FLASH
IS IGNITOR INTACT AND CONNECTED?
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?
NO
YES
FLAME RECTIFICATION CURRENT
CHECK. CAN FLAME BE PROVEN WITHIN
4 SECONDS AFTER GAS VALVE OPENS?
(>0.15 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
FLAME PRESENT?
YES
NO
LOW FLAME SIGNAL
(Does not affect operation of control)
LED #1 -- SLOW FLASH
LED #2 -- FAST FLASH
FLAME SIGNAL ABOVE 0.7 MICROAMPS?
YES
INDOOR BLOWER ON DELAY BEGINS
(45 seconds.)
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
NO
PRIMARY AND SECONDARY LIMIT
SWITCHES CLOSED?
NO
HAS CONTROL RESET IGNITION
SEQUENCE FOUR TIMES?
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 2 DIAGNOSTIC CODES for limit reset operation)
NO
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
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 28
5-MINUTE PRESSURE SWITCH
WATCHGUARD MODE.
YES
SURELIGHT CONTROL COOLING SEQUENCE
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?
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?
NO
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. TERM. ENERGIZED.
THERMOSTAT OPENS.
COMPRESSOR OFF.
ACB COOL SPEED AND ACC. TERM. OFF
WITH 0-SECOND DELAY.
3DJH 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 30
E--SureLight Ignition Control Troubleshooting Guide
UPON INITIAL POWER UP, REMOVE ALL THERMOSTAT DEMANDS TO THE UNIT
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 Main voltage 120V not supplied to
up.
unit.
--
1.1.2
Miswiring of furnace or improper
connections.
LED#1--Off
LED#2--Off
1.1.3
Circuit breaker tripped or fails to
close.
Corrective Action / Comments
ACTION 1 -- Check 120V main voltage.
Determine cause of main power failure.
ACTION 1 -- Check for correct wiring of 120V
to power make up box and transformer.
ACTION 2 -- Check 24V wiring to control
board.
ACTION 1 -- Replace circuit breaker if it is reset but does not have continuity.
ACTION 2 -- If circuit breaker still trips, check
for short.
ACTION 1 -- Check that door switch is activated
1.1.4
Door interlock switch failure.
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.
1.1.6
Failed control board.
1.2
Diagnostic lights flash the roll-out code.
--
LED#1--On,
LED#1
O
LED#2--Slow
LED#2
Slow Flash
1.2.1
ACTION 1 -- Check that transformer output is
24V. Replace if malfunctioning
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.
Roll--out switch open.
ACTION 2 -- Determine the cause of the roll--
1.2.2
ACTION 1 -- Check continuity across roll--out
Roll--out switch failure.
1.2.3
Mis iring or improper connections
Miswiring
at roll--out switch.
1.2.4
Nine pin connector failure
out switch activation before leaving furnace.
switch. Replace roll--out switch if switch is
reset but does not have continuity.
ACTION 1 -- Check wiring connections to
switch.
ACTION 1 -- Check 9--pin connector for proper connection to control board.
ACTION 2 -- Check continuity of the multi
plug pin.
1.3
-- On initial power--up the comb. air
blower does not energize.
1.3.1
-- Diagnostic lights flash the reverse polarity code.
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 air blower does not energize. Open combustion air blower motor
-- Diagnostic lights flash normal circuit.
power on operation.
operation
ACTION 1 -- Check for 120V to combustion air
blower. If no power, check wire and connections.
1.4.2
LED#1--Slow Flash
LED#2--Slow Flash
Failed combustion air blower motor.
3DJH 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 combusg
tion air blower remains energized.
-- Diagnostic
flash
the iimDi
ti lilights
ht fl
h th
proper main ground.
--
LED#1--Alternating Fast Flash
LED#2--Alternating Fast Flash
Possible Cause
1.5.1
Improper ground to the unit.
1.5.2
6--Pin connector is improperly attached to the circuit board.
1.5.3
Line voltage is below 75V.
Corrective Action / Comments
ACTION 1 -- Check that the unit is properly
ground.
ACTION 2 -- Install a proper main ground to
the unit
ACTION 1 -- Check 6--pin connector for proper
installation. Correctly insert connector into
control.
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 OPERATES IN COOLING MODE BUT NOT IN THE HEATING MODE, WITH
COMBUSTION AIR BLOWER CYCLING 5 SECONDS ON 55 SECONDS OFF.
Condition
Possible Cause
Corrective Action / Comments
2.1
On initial power--up the combustion air blower remains energized.
-- Diagnostic lights flash the im
proper main ground.
-- Combustion air blower cycles 5
seconds on 55 seconds off.
--
2.1.1
Open ignitor circuit.
2.1.2
LED#1--Alternating Fast Flash
LED#2--Alternating Fast Flash
Broken or failed ignitor.
ACTION 1 -- Check for correct wiring and
loose connections in the ignitor circuit. Check
mult--plug connections for correct installation.
ACTION 1 -- Unplug ignitor and read resistance across ignitor. If resistance does not
read between 10.9 and 19.7 ohms, replace the
ignitor.
PROBLEM 3: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER DOES
NOT ENERGIZE
Condition
Possible Cause
3.1
Unit operates with a cooling or
3.1.1
continuous fan demand.
Primary
or
secondary
(if equipped)
-- Combustion air blower will not
limit
open.
start with a Heating demand.
-- Diagnostic lights flash the limit
failure mode.
mode
--
3.1.2
LED#1--Slow Flash,
LED#2--On
Miswiring of furnace or improper
connections at limit switch(es).
Corrective Action / Comments
ACTION
1
switch(es).
--
Check
Switches
continuity
reset
across
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.
ACTION 1 -- Check for correct wiring and
loose connections. Correct wiring and/or replace any loose connections.
3.2
-- Unit operates with a cooling and
continuous fan demand.
-- Combustion air blower will not
start with a Heating demand.
-- Diagnostic lights flash the pressure switch failure code.
code
LED#1--Off,
LED#2--Slow Flash
3.2.1
Miswiring of furnace or improper
connections to combustion air
blower.
ACTION 1 -- Check for correct wiring and
3.2.2
ACTION 1 -- Check that the pressure switch is
Pressure switch stuck closed.
3DJH loose connections. Correct wiring and/or replace any loose connections.
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
Corrective Action/Comments
3.3
-- Unit operates with a cooling and
continuous fan demand.
-- Combustion air blower will not
start with a Heating demand.
-- Diagnostic lights flash the pressure switch failure code 2.5 minutes
after heating demand.
LED#1--Off,
LED#2--Slow Flash
3.3.1
Miswiring of furnace or improper
connections to combustion air
blower.
ACTION 1 -- Check for correct wiring and
3.3.2
ACTION 1 -- If there is 120V to combustion air
Combustion air blower failure.
loose connections. Correct wiring and/or replace any loose connections.
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
4.1
4.1.1
Unit operates with a cooling and
Pressure switch does not close
continuous fan demand.
due to incorrect routing of the
-- Combustion air blower enerpressure switch lines.
gizes with a heating demand.
demand
4.1.2
-- Diagnostic lights flash the presPressure
switch
does not close
sure switch failure code 2.5 mindue
to
obstructions
in the pressure
utes after heating demand.
lines.
--
LED#1--Off
LED#2--Slow
LED#2
Slow Flash
4.1.3
Pressure switch lines damaged
Corrective Action/Comments
ACTION 1 -- Check that the pressure switch
lines are correctly routed. Correctly route
pressure switch lines.
ACTION 1 -- Remove any obstructions from
the the pressure lines and/or taps.
ACTION 1 -- Check pressure switch lines for
leaks. Replace any broken lines.
ACTION 1 -- Check the differential pressure
across the pressure switch. This pressure
should exceed the set point listed on the
4.1.4
Pressure switch does not close
due to a low differential pressure
across the pressure switch.
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 thre combustion air blower.
4.1.5
Wrong pressure switch installed in
the unit, or pressure switch is out
of calibration.
4.1.6
Miswiring of furnace or improper
connections at pressure switch.
4.1.7
Pressure switch failure.
3DJH ACTION 1 -- Check that the proper pressure
switch is installed in the unit. Replace pressure switch if necessary.
ACTION 1 -- Check for correct wiring and
loose connections. Correct wiring and/or replace any loose connections.
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.
PROBLEM 5: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER
ENERGIZES, IGNITOR IS ENERGIZED. (CONT.)
Condition
5.1
Possible Cause
5.1.1
-- Unit operates with a cooling and Check that gas is being supplied to
continuous fan demand.
the unit.
-- Combustion air blower enerener
5.1.2
gizes with Heating demand.
Miswiring of gas valve or loose
-- Ignitor is energized but unit fails
connections at multi--pin control
to light.
amp plugs or valve.
Corrective Action/Comments
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.
ACTION 1 -- Check for correct wiring and
loose connections. Correct wiring and/or replace any loose connections.
ACTION 1 -- Check that 24V is supplied to the
gas valve approximately 35 seconds after
LED#1--Alternating Slow Flash
LED#2--Alternating Slow Flash
5.1.3
Malfunctioning gas valve or ignition control.
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.
PROBLEM 6: BURNERS LIGHT WITH A HEATING DEMAND BUT UNIT SHUTS DOWN
PREMATURELY
Condition
Possible Cause
Corrective Action/Comments
6.1.1
ACTION 1 -- Check for restricted vent inlet or
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.
Low pressure differential at the
pressure switch.
exhaust. Remove all blockage.
ACTION 2: Check for proper vent sizing. See
installation instructions.
LED#1--Off
LED#2--Slow Flash
6.2
6.2.1
-- Combustion air blower energizes Sensor or sense wire is improperly
with a heating demand.
installed.
-- B
Burners lilight
ht b
butt ffail
il tto stay
t lit
lit.
6.2.2
-- After 5 tries the control diagnostics flash the watchguard burners
Sensor or sense wire is broken.
failed to ignite code.
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.
ACTION 1 -- Check for a broken sensor.
ACTION 2 -- Test continuity across the sense
wire. If wire or sensor are damaged replace
the component.
ACTION 1 -- Check for resistance between
LED#1--Alternating Slow Flash
LED#2--Alternating Slow Flash
6.2.3
Sensor or sensor wire is grounded
to the unit.
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.
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 contamina-
6.2.4
Control does not sense flame.
tion.
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.
3DJH PROBLEM 6: BURNERS LIGHT WITH HEATING DEMAND BUT UNIT SHUTS DOWN
PREMATURELY (CONT.)
Condition
Possible Cause
Check that the manifold pressure
matches value listed on nameplate. See
installation instructions for proper procedure.
Verify that the installed orifice
size match the size listed on the nameplate or
installation instructions.
Check gas valve sensing hose to
insure no leaks are present.
Check the input rate to verify rate
matches value listed on nameplate.
Tightenorifice untilleakissealed.
Be careful not to strip orifice threads.
Check for gas leakage at the
threaded orifice connection. Use approved
method for leak detection (see unit instructions).
Checkforsootingdepositsorother restrictions in the heat exchanger assembly. Clean assemblyas outlined in instruction
manual.
For G24M gas furnaces, check for
proper combustion and flow. CO2 should
measure between 6.0% and 8.0% for NG and
between 6.5% and 8.5% for LP. CO should
measure below .04% (400PPM) in an air--free
sample of flue gases for either NG or LP.
Check that the burners are firing
into the center of the heat exchanger openings. Correct the location of the burners if
necessary.
ACTION 1 --
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.
Corrective Action/Comments
6.3.1
Unit is firing above 100% of the
nameplate input.
ACTION 2 --
ACTION 3 -ACTION 4 --
ACTION 1 --
LED#1--On
LED#2--Slow Flash
6.3.2
Gas orifices leak at the manifold
connection.
NOTE:
ACTION 2 --
ACTION 1 --
6.3.3
Insufficient flow through the heat
exchanger caused by a sooted or
restricted heat exchanger.
6.3.4
Burners are not properly located in
the burner box.
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
6.4.1
Recirculation of flue gases. This
condition causes rough ignitions
and operation. Problem is characterized by nuisance flame failures.
6.4.2
Improper burner cross--overs
3DJH ACTION 2 --
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.
Check for correct intake and exhaust vent installation. See instructions
ACTION 1 --
ACTION 2 --
Remove burner and inspect the
cross--overs for burrs, or any restriction or if
crossover is warped. Remove restriction or
replace burners.
ACTION 1 --
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.
Check that the sensor is properly
located.
Checkthatthesense wireisproperly attached to both the sensor and the control.Payextraattentiontothe pinconnectors.
ACTION 1 -ACTION 2 --
LED#1--Alternating Slow Flash
LED#2--Alternating Slow Flash
PROBLEM 7: CONTROL SIGNALS LOW FLAME SENSE DURING HEATING MODE
Condition
Possible Cause
7.0
7.1.1
-- Unit operates correctly but the
diagnostic lights flash low flame
sense code.
code
Sense rod is improperly located on
the burner.
Corrective Action/Comments
Check the sense rod for proper
location on the burner. Properly locate the
sense rod or replace if rod cannot be located
correctly.
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.
ACTION 1 --
ACTION 1 --
7.1.2
LED#1--Slow Flash
LED#2--Fast Flash
Sense rod is contaminated.
PROBLEM 8: INDOOR BLOWER FAILS TO OPERATE IN COOLING, HEATING, OR CONTINUOUS
FAN MODE
Condition
Possible Cause
8.0
8.1.1
-- Indoor blower fails to operate in
continuous fan, cooling, or heating
mode.
Miswiring of furnace or improper
connections at control or indoor
blower motor.
Corrective Action/Comments
Correct wiring and/or replace any
loose connections. Check for correct wiring
and loose connections.
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.
If there is not 120V when ”Y”,
”G”, or ”W” is energized, replace the control.
ACTION 1 --
8.1.2
120V is not being supplied to the
indoor air blower or blower motor
failure.
8.1.3
Defective control board
ACTION 1 --
PROBLEM 9: RF STATIC DURING TIME FOR IGNITION
Condition
Possible Cause
9.0
9.1.2
-- AM radio interference.
Ignitor operation
3DJH Corrective Action/Comments
ACTION 1 -- Call Technical Support, Dallas.