Post on 06-Feb-2018
Page 1 1998 Lennox Industries Inc.Litho U.S.A.
Corp. 9723-L12
G24MService Literature Revised 07-2001
G24M SERIES UNITSG24M series units are mid-efficiency gas furnaces manufac-tured with tubular steel heat exchangers formed of alumi-nized steel. G24M units are available in heating capacities of45,000 to 140,000 Btuh and cooling applications up to 5tons. Refer to Engineering Handbook for proper sizing.Units are factory equipped for use with natural gas. A kit isavailable for conversion to LPG operation. Early model G24Munits use electronic (direct spark) ignition. Late model G24Mmodel units feature the Lennox SureLightT silicon-nitrideignition system. The G24MX unit meets the California Nitro-gen Oxides (NOx) Standards and California Seasonal Effi-ciency requirements. All units use a redundant gas valve toassure safety shut-off as required by A.G.A. or C.G.A.Units may be installed in upflow, downflow or horizontal posi-tion. The heat exchanger is designed for upright or horizon-tal use only. When the unit is installed in the downflow posi-tion, the heat exchanger is field removed and reinstalled so itis upright when the cabinet is inverted. No field conversion isrequired when the unit is installed in the horizontal position.
The heat exchanger, burners and manifold assembly caneasily be removed for inspection and service by simply dis-connecting gas, unplugging wiring harness and spark wiresand removing four screws holding the heat exchanger inplace. Then the heat exchanger slides out of the cabinet.
All specifications in this manual are subject to change. Pro-cedures outlined in this manual are presented as a recom-mendation only and do not supersede or replace local orstate codes. In the absence of local or state codes, theguidelines and procedures outlined in this manual (exceptwhere noted) are recommended only and do not constitutecode.
SPECIFICATIONSModel No. G24M2(X)-45 G24M2-60 G24M3(X)-60 G24M2-75 G24M3(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)lA.F.U.E. 80.1% 80.5% 80.5% 80.1% 80.0%California Seasonal Efficiency 75.4% 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)
Blower wheel nominal in. 9 x 7 10 x 7 9 x 7 10 x 7Blower wheel nominaldiameter x width mm 229 x 178 254 x 178 229 x 178 254 x 178
Blower motor output — hp (W) 1/4 (187) 1/3 (224) 1/4 (187) 1/3 (224)Nominal cooling Tons 1, 1-1/2 or 2 2, 2-1/2 or 3 1, 1-1/2 or 2 2, 2-1/2 or 3Nominal cooling
that can be added 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 10.6Shipping 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)bLPG/propane kit LB-69845L (38K84)Twinning Kit 96J69 — 5 lbs. (2 kg)Up-Flow/Horizontal Filter and Filter Rack Kits}No. & size of filters - in. (mm)
Single (32J02) Ten Pack (66K64)(1) 16 x 20 x 1 (406 x 508 x 25)
¡Down-flowCatalog No. LB-69843A (32J01) — 3 lbs. (1 kg)
¡Down-flowFilter Kit 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 LB-69957 (46J66) — 15 lbs. (8 kg)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.
3DJH �
SPECIFICATIONS
Model No. G24M4(X)-75 G24M3/4(X)-100 G24M4/5(X)-100
Input Btuh (kW) 75,000 (22.0) 100,000 (29.3)
Output Btuh (kW) 61,700 (18.1) 82,000 (24.0)
RA.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 � EF (EC) 45 - 75 (25 - 42) 35 - 65 (19 - 36)
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)
Blower wheel nominalin. 12 x 8 12 x 9
Blower wheel nominaldiameter x width
mm 305 x 203 305 x 229
Blower motor output � hp (W) 1/2 (373) 3/4 (560)
Nominal coolingTons 2, 2-1/2, 3, 3-1/2 or 4 3-1/2, 4, 5 or 6
Nominal coolingthat can be added
kW 7.0, 8.8, 10.6, 12.3 or 14.1 12.3, 14.1, 17.6 or 21.1
Shipping weight � lbs. (kg) 1 package 140 (64) 175 (79) 175 (79)
Electrical characteristics 120 volts � 60 hertz � 1 phase (less than 12 amps) All models
H Optional Accessories (Must Be Ordered Extra) H
LPG/propane kit LB-69845L (38K84) LB-69845K (81J14)
Twinning Kit 96J69� 5 lbs. (2 kg)
Up--Flow/Horizontal Filter and Filter Rack KitscNo. & size of filters -- in. (mm)
Single (32J02) Ten Pack (66K64)(1) 16 x 20 x 1 (406 x 508 x 25)
Single (46J14) Ten Pack (66K65)(1) 20 x 20 x 1 (508 x 508 x 25)
Catalog No. LB-69843A (32J01)� 3 lbs. (1 kg)
oDown-flowFilter Kit 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) LB-79239B (67J92)� 10 lbs. (4 kg)
Sidewall Power Venting Kit 79J15� 25 lbs. (11 kg)
Hanging Bracket Kit LB-69957 (46J66)� 15 lbs. (8 kg)
RAnnual Fuel Utilization Efficiency based on U.S. DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherizedfurnaces.cPolyurethane frame type filter is furnished with kit.oFilters are not furnished with kit and must be ordered extra.
3DJH �
SPECIFICATIONS
Model No. G24M3/4-120 G24M4/5(X)-120 G24M4/5-140
Input Btuh (kW) 120,000 (35.2) 140,000 (41.0)
Output Btuh (kW) 98,400 (28.8) 114,800 (33.6)
RA.F.U.E. 80.0% 80.1% 80.0%
California Seasonal Efficiency Not Available 75.5% Not Available
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)
Blower wheel nominalin. 12 x 8 12 x 9Blower wheel nominal
diameter x width mm 305 x 203 305 x 229
Blower motor output � hp (W) 1/2 (373) 3/4 (560)
Nominal cooling Tons 2, 2-1/2, 3, 3-1/2 or 4 3-1/2, 4, 5 or 6Nominal coolingthat can be added kW 7.0, 8.8, 10.6, 12.3 or 14.1 12.3, 14.1, 17.6 or 21.1
Shipping weight � lbs. (kg) 1 package 175 (79) 190 (86)
Electrical characteristics 120 volts � 60 hertz � 1 phase (less than 12 amps) All models
H Optional Accessories (Must Be Ordered Extra) H
LPG/propane kit LB-69845K (81J14)
Twinning Kit 96J69� 5 lbs. (2 kg)
Up--Flow/Horizontal Filter and Filter Rack KitscNo. and size of filters -- in. (mm)
Single (46J14) Ten Pack (66K65)(1) 20 x 20 x 1 (508 x 508 x 25)
Single (58J93) Ten Pack(66K66)
(1) 20 x 20 x 1 (508 x 508 x 25)Catalog No. LB-69843A (32J01)� 3 lbs. (1 kg)
wDown-flowFilter Rack No. & Size in. (2) 16 x 20 x 1Filter Rack No. & Size
of Filters mm (2) 406 x 508 x 25
Down-flow Combustible Floor Base LB-79239B (67J92)� 10 lbs. (4 kg)LB-79239C (67J93)� 12 lbs. (5 kg)
Sidewall Power Venting Kit 79J15� 25 lbs. (11 kg)
Hanging Bracket Kit LB-69957 (46J66)� 15 lbs. (8 kg)
RAnnual Fuel Utilization Efficiency based on U.S. DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherizedfurnaces.c Polyurethane frame type filter is furnished with kit.o2 in. x 5 in. (51 mm x127 mm) flue adaptor furnished with -140 input furnaces for connection to furnace induced draft blower.wFilters are not furnished with kit and must be ordered extra.
BLOWER DATA
G24M2-45, G24M2-60 AND G24M2-75 BLOWER PERFORMANCE
External Static Air Volume at Various Blower SpeedsExternal StaticPressure 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
External Static Air Volume at Various Blower SpeedsExternal StaticPressure 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
External StaticAir Volume at Various Blower Speeds
External StaticPressure 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
External StaticAir Volume at Various Blower Speeds
External StaticPressure 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
FIGURE 1
G24MPARTS IDENTIFICATION
VENT ADAPTERCABINET TOP
G24MCABINET
CABINETBOTTOM
HEAT EXCHANGERASSEMBLY
BURNERASSEMBLY
BLOWER ASSEMBLY
COMBUSTION AIRBLOWER
FLUE BOX
SECONDARYLIMITS
FRONT LOUVEREDPANEL
DOOR INTERLOCK SWITCH
CONTROLBOARD
TRANSFORMER
PRESSURESWITCH
NOxTURBULATOR
LOW PRESSURE SWITCH(Propane Only)
PRIMARYLIMIT
FIGURE 2
HEATING COMPONENTS (shown in horizontal position)
HEAT EXCHANGER
COMBUSTION AIR BLOWER
MANIFOLD
ROLLOUT SWITCH (2)
COMBUSTION AIRPROVE SWITCH
GAS VALVE
BURNERS
COLLECTOR
PRIMARY LIMIT
ORIFICES
Front
Right
Top
Bottom
Left
Back
Page 7
FIGURE 3
Top
G24M BURNER ASSEMBLY(shown in upflow position with SureLight ignition system)
FLAMESENSOR
MANIFOLD
ORIFICE
GAS VALVE
HEAT EXCHANGER
VEST PANEL
BURNER
UPPERBURNER
MOUNTINGRAIL
LOWERBURNER
MOUNTINGRAIL
BURNER BOX
BURNER BOXTOP
FrontRight
Bottom
LeftBack
PRIMARY LIMIT
ROLLOUTSWITCHES
SURELIGHTIGNITOR
FIGURE 4
To Access Blower:
1-- Turn off power to unit and disconnect L1and L2 line voltage power.
2-- Disconnect thermostat wiring connec-tions from furnace control board.
3-- Remove screws (2) from blower panel.
4-- Disconnect J135 from P135 from limitcontrol.
5-- Disconnect J43 from blower motor.
6-- Remove blower panel and lift from unit.
G24M BLOWER DOOR COMPONENTS -- BLOWER ACCESS
Top
Bottom
Left
RightBack
Front
4
1
J1/P1
J135/P135
2
3
5
6
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Page 9
SURELIGHT CONTROL BOARDLATE MODEL G24M UNITS
FIGURE 6
SURELIGHT CONTROL TERMINAL DESIGNATIONSACB COOLACB HEATPARKACB LOWACCTXHOTHTG ACCNEUTRALS24VAC HOT24VAC RTNFLAME SENSE
Blower - Cooling Speed (Line Volt)Blower - Heating Speed (Line Volt)Alternate Blower Speeds (Dead)Continuous Low Speed BlowerAccessory Terminal (Line Volt)120VAC Hot to Transformer120VAC Hot InputHeat Only Accessory (Line Volt)120VAC Neutrals24VAC Hot from Transformer24VAC Return from TransformerFlame Sense Terminal
TABLE 1
FIGURE 7
NORMAL FLAME SIGNAL > 0.7 MICROAMPSLOW FLAME SIGNAL < 0.7 MICROAMPSMINIMUM FLAME SIGNAL < 0.15 MICROAMPS
FLAME SENSOR TO BURNER GAP
BURNER
FLAMESENSORSIDE VIEW END VIEW
1/4 in. 7 mm¦ 1/32 in. 0.79
mm3/16 in.4.7 mm
11/16 in. 18 mm¦ 1/32 in. 0.79
mm
TABLE 2DIAGNOSTIC CODES
MAKE SURE TO ID LED’S CORRECTLY: REFER TO INSTALLATION INSTRUCTIONS FOR CONTROL BOARD LAYOUT.
LED #1 LED #2 DESCRIPTIONSIMULTANEOUS
SLOW FLASHSIMULTANEOUS
SLOW FLASHPower - Normal operation
Also signaled during cooling and continues fan.
SIMULTANEOUS FASTFLASH
SIMULTANEOUS FASTFLASH Normal operation - signaled when heating demand initiated at thermostat.
SLOW FLASH ON
Primary or Secondary limit open. Units with board 63K8901 or 24L85: Limit mustclose 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 FLASHPressure switch open or has opened 5 times during a single call for heat; OR:
Blocked inlet/exhaust vent; OR: Condensate line blocked; OR: Pressure switchclosed prior to activation of combustion air blower.
ALTERNATING SLOWFLASH
ALTERNATING SLOWFLASH 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.
ONONOFF
ONOFFON
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 FASTFLASH
ALTERNATING FASTFLASH
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 10
TABLE 3
SureLight BOARD J156 (J2) TERMINALDESIGNATIONS
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 4
SureLight BOARD J58 (J1) TERMINALDESIGNATIONS
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
CAUTIONElectrostatic discharge can affect electroniccomponents. Take precautions during furnaceinstallation and service to protect the furnace’selectronic controls. Precautions will help toavoid control exposure to electrostatic dis-charge by putting the furnace, the control andthe technician at the same electrostatic poten-tial. Neutralize electrostatic charge by touchinghand and all tools on an unpainted unit surface,such as the gas valve or blower deck, before per-forming any service procedure.
ELECTROSTATIC DISCHARGE (ESD)Precautions and Procedures
b-Electronic IgnitionOn a call for heat the SureLight control monitors the com-bustion air inducer prove switch. The control will not beginthe heating cycle if the prove switch is closed (by-passed).Once the prove switch is determined to be open, the com-bustion air inducer is energized. When the differential inthe prove switch is great enough, the prove switch closesand a 15-second pre-purge begins. If the prove switch is
not proven within 2-1/2 minutes, the control goes intoWatchguard-Pressure Switch mode for a 5-minute re-setperiod.
NOTE - The G24M furnace contains electronic com-ponents that are polarity sensitive. Make sure that thefurnace is wired correctly and is properly grounded.
After the 15-second pre-purge period, the SureLight igni-tor warms up for 20 seconds after which the gas valveopens for a 4-second trial for ignition. The ignitor stays en-ergized for the first second of the 4-second trial. G24Munits with 63K89, 24L85 or 56L83: the ignitor stays ener-gized the first second of the 4 second trial. G24M units withboard 97L48: ignitor stays energized during the 4-secondtrial until flame is sensed. If ignition is not proved during the4-second period, the control will try four more times with aninter purge and warm-up time between trials of 35 sec-onds. After a total of five trials for ignition (including the ini-tial trial), the control goes into Watchguard-Flame Failuremode. After a 60-minute reset period, the control will beginthe ignition sequence again.The SureLight control board has an added feature thatprolongs the life of the ignitor. After a successful ignition,the SureLight control utilizes less power to energize the ig-nitor on successive calls for heat. The control continues toramp down the voltage to the ignitor until it finds the lowestamount of power that will provide a successful ignition.This amount of power is used for 255 cycles. On the 256thcall for heat, the control will again ramp down until the low-est power is determined and the cycle begins again.
c-Fan Time ControlThe fan on time of 45 seconds is not adjustable. Fan offtime (time that the blower operates after the heat demandhas been satisfied) can be adjusted by flipping the dipswitches located on the SureLight integrated control. Theunit is shipped with a factory fan off setting of 90 seconds.Fan off time will affect comfort and is adjustable to satisfyindividual applications. See figure 8.
NOTE—If fan “off” time is set too low, residual heat inheat exchanger may cause primary limit S10 to trip re-sulting in frequent cycling of blower. If this occurs, ad-just blower to longer time setting.
FIGURE 8
FAN-OFF TIME ADJUSTMENT
To adjust fan-off timing, flip dip switch to desired setting.
60sec. 90sec. 120sec. 180sec.
Page 11
4-- Ram Control (A3)Early Model G24M Units
The furnace control combines burner ignition func-
tions with blower control functions.
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 igni-
tion spark. It alsomonitors 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 equippedwith a diagnos-
tic 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 be-
gins flashing at a fast rate and the combustion air
blower is energized. TheLED flashesdifferent codes to
indicate problem conditions. The diagnostic LED lights
red (not flashing) to indicate control board failure. Table
7 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 com-
bustion products and to introduce fresh air for com-
bustion. If the combustion air prove switch does not
close, the combustion air blower continues to run in-
definitely (until the prove switch closes).
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.
Ignition Control
The ignition control is a direct spark ignition control
module integral to the furnace control. See figure 9.
When there is a call for heat, the control delays ignition
until combustion air blower operation has been proved
andpre-purgeperiodhas elapsed. It thenopens thegas
valve and generates a spark to ignite the burners. Trial
for ignition lasts for 7 seconds. At the same time, the
control beginsmonitoring the flamesensor. If the flame
current is too weak (less than 1 microamp) or if the
burners donot ignite (within the 7 second ignition trial),
the control will shut off the spark ignitor and the com-
bustion air blower and de-energize the gas valve.
Flamecurrent shouldbebetween1and5microamps 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 beginswith a45secondpre-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 60minutes. At the
end of 60 minutes the control completely resets and
will attempt ignition up to three times. The control can
bemanually reset before the end of 60minutes bymo-
mentarily turning off power to the unit.
DANGERShock hazard.
Spark related components contain high voltage.Disconnect powerbefore servicing. Control is notfield repairable. If control is inoperable, simply re-place entire control.
Can cause injury or death. Unsafe operation willresult if repair is attempted.
Page 12
EARLY MODEL G24M FURNACE CONTROL (A3)
FIGURE 9
LINE VOLTAGETERMINAL
CONNECTIONS
24VAC VOLTTERMINAL
CONNECTIONS
THERMOSTATCONNECTIONS
DIAGNOSTICLED
See Table 6 forTerminalFunctions
FAN-OFF TIMINGSWITCHES
SPARK OUTPUT
PLUG P20
TABLE 5
Furnace Control A3 Limit Response During Operation
Response
ConditionCombustion
AirBlower
GasValve
SupplyAir
Blower
DiagnosticLED
Loss of FlameSensed BeforeEnd of 45 se-cond BlowerOn Delay(3 or Fewer
Trialsfor Ignition)
On
On(SparkStarts
Within 0.8seconds)
On Fast Flash
Loss of FlameSensed After45 secondBlower OnDelay (3 orFewer Trialsfor Ignition)
On
Off ThenOn WithSpark
After Pre-Purge
On Fast Flash
Loss of FlameSensed (MoreThan 3 Trialsfor Ignition)
Off Off Off 2 Flashes
Flame SensedWithoutDemand
On Off On 5 Flashes
Primary orSecondaryLimit Open
On Off On 4 Flashes
Rollout SwitchOpen
On Off On 4 Flashes
CombustionAir Prove
Switch OpenOn Off On 3 Flashes
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 thermo-
stat demand, the gas valve closes and the diagnostic
LED registers the error condition (table 5).
Blower Control and Timings
DANGERElectrical Shock Hazard.This control contains field adjustable switchesand also contains line voltage. Make sure poweris disconnected before making any field adjust-ments or 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.
Fan�ON� timing (time that the burners operate before
the supply air blower starts) is fixed at 45 seconds and
cannot be adjusted.
Fan �OFF� timings (time that the blower operates after
a heating or coolingdemandhas been satisfied) are de-
termined by the arrangement of switches on the fur-
nace control board. See figure 9. To adjust fan �off �
timings, gently reposition the switches to a new timing
Page 13
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�
time will affect comfort and efficiency and is adjustable
to satisfy individual applications. The fan �off� timing is
initiated after a heatingor coolingdemandbut not after a
blower demand (that is, when indoor thermostat switch
is changed from ON to AUTO and heating/cooling de-
mand is not present, the blower stops immediately).
TABLE 6
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
R Screw Strip 24VAC to Thermostat
W Screw Strip Heating Demand
C Screw Strip 24VAC Common
120VAC HOT 1/4� Spade Line Voltage In
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 toCombustion Air Blower
CMB RTN J20/P20 Pin 2120VAC Common
Combustion Air Blower
ACB HEAT 1/4� Spade Switched 120VAC toBlower Heating Tap
ACB LOW 1/4� Spade120VAC Output to Supply AirBlower for Continuous Opera-
tion During No Demand
ACB COOL 1/4� Spade Switched 120VAC to BlowerCooling Tap
VLV HOT J20/P20 Pin 13 24VAC to Gas Valve
VLV RTN J20/P20 Pin 924VAC Common From
Gas Valve
PSW INJ20/P20Pin 10
24VAC In From Pressure SwitchSwitch Open: Prohibits IgnitionSwitch Closed: Allows Ignition
HIL INJ20/P20Pin 11
24VAC In From LimitsLimit Open: Closes Gas ValveLimits Closed: Allows Ignition
HIL OUTJ20/P20Pin 14
24VAC to Limit Trainand Pressure Switch
RO OUT J20/P20 Pin 7 24VAC Out To Rollout Switches
RO IN J20/P20 Pin 15 24VAC In From Rollout Switches
SPARKELECTRODE
Male SparkPlug Type
High Voltage Out ToSpark Electrode
FS J20/P20 Pin 12 Flame Microamp Sensing
FIGURE 10
FAN-OFF TIME ADJUSTMENT SWITCHESLOCATED ON FURNACE CONTROL (A3)
Fan-Off Timings
Switch
1 2TimingSeconds
Off
OnOff
Off
OffOn
On On
120
90
180
240
Diagnostic LED
The furnace control is equippedwith a diagnostic LED
used for troubleshooting the unit and the control. LED
functions are shown in table 7.
TABLE 7
Furnace Control A3 Diagnostic LED
LED State Meaning Remedy
Steady On Control Failure Replace Control
Slow FlashNormal Operation
and No Call For Heat- - - -
Fast FlashNormal Operationwith Call For Heat
- - - -
TwoFlashes
Control Lockout
Failed to Sense or SustainFlame. Check Gas Valve,Burners, Spark Electrodeand Wire, Flame Sensor.Replace Control If All OK.
ThreeFlashes
Pressure Switch Open
Failed to Prove Combus-tion Blower Operation orBlocked Vent. Repair orReplace as Necessary.
FourFlashes
Open Limit
Check Primary Limit,Rollout Switches and Sec-ondary Limits. Find sourceof Overtemperature. If allOK, Reset or Replace Lim-
its as Necessary.
FiveFlashes
Flame Sensed and GasValve Not Energized.
Check Gas Valve. If OK,Check Flame Sensor.
B--Blower Motors and Capacitors
All G24M units use direct drive blower motors. All mo-
tors used are 120V permanent split capacitormotors to
ensure maximum efficiency. See table8 for ratings.
TABLE 8
G24M BLOWER RATINGS 120V 1PHBLOWER MOTOR HP
G24MQ2
G24MQ3
G24MQ3/4
CAP
1/2
1/3
1/4 5MFD 370V
5MFD 370V
7.5MFD 370V
G24MQ5/6
G24MQ4
G24MQ4/5
1/2 7.5MFD 370V
3/4 40MFD 370V
3/4 40MFD 370V
FIGURE 11
SUPPLY AIR BLOWER
AND SECONDARY LIMITS
FrontBottom
Right
Left
TopBack
BLOWERMOTOR
To Remove Blower From Unit: Remove Bolts andWiring Jackplugs. Then Slide Out Front of Unit.
MOTORCAPACITOR
SECONDARYLIMITS (S21)
Page 14
C--Combustion Air Blower (B6)
All G24M units use a combustion air blower to move
air through the burners and heat exchanger during
heating operation. Some early model G24M units are
equipped with a blower that uses a PSC (Permanent
Split Capacitor) 120VAC motor. PSC motors use run
capacitors. Other early and latemodel G24Munits are
equipped with a blower that uses a shaded pole 120V
motor. The motor operates during all heating opera-
tion and is controlled by furnace control A3. For G24M
units equipped with the Ram ignition system, the
blower will operate for 45 seconds before burner igni-
tion (pre-purge) and for 5 seconds after the gas valve
closes (post-purge). ForG24Munits equippedwith the
SureLight ignition system, the blower will operate for
15 secondsbeforeburner ignition (prepurge) and for 5
seconds after the the gas valve closes (post purge).
A pressure switch connected to the combustion airblower housing is used to prove combustion air bloweroperation. The switchmonitors air pressure in the blow-er housing.During normal operation, thepressure in thehousing 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 burneroperation.
D--Flame Rollout Switches (S47)Flame rollout switch is a high temperature limit lo-
cated 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 controlA3.WhenS47senses rollout,
the ignition control immediately stops ignition and
closes the gas valve. If unit is running and flame roll-
out 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.
FIGURE 12
ROLLOUT SWITCH (S47)
MANUAL
RESET BUTTON
E--Primary Limit Control (S10)
FIGURE 13
G24M SERIES UNITSLIMIT CONTROL FOR
THIS TYPE AUTO-RESET LIMIT
IS USED FOR THE PRIMARY LIMIT (S10) AND
RIGHT SECONDARY LIMIT (S21)
(see FIGURE 11)
The primary limit (S10) on G24M units is located in the
middle of the heating vestibule panel. Whenexcess 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 automati-
cally resets when unit temperature returns to normal.
The switch is factory set and cannot be adjusted. The
switchmayhavedifferent setpoints for eachunitmodel
number. However, the setpoint will be printed on the
side of the limit.
F--Secondary Limit Controls (S21)The secondary limit (S21) onG24Munits 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 tonormal. Theswitch is factory
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, re-
place with limit kit no. 50L98.
INSULATING COVER (s)
FIGURE 14
SECONDARY LIMIT CONTROL (S21)FOR G24M SERIES UNITS
SPADECONNECTORS
INSULATINGCOVER
LIMIT
LIMIT
THIS TYPE AUTO-RESET LIMIT IS
USED FOR THE LEFT SECONDARY
LIMIT (S21) (see FIGURE 11)
G--Spark Electrode and Flame SensorEarly Model G24M Units
Figure 15 shows the arrangement of flame sensor,spark electrode and burners. The ignition control usesdirect spark to ignite the rightmost burner and theburners cross-light to the left. The flame sensor usesflame rectification to sense combustion. A flameretention ring in the end of each burner is used tomaintain correct flame length and shape and to keepthe flame from lifting off the burner head.
Figure 16 shows the gap between tip of the electrodes
and the burner surface.
Page 15
FIGURE 15
TYPICAL BURNER/ELECTRODE ORIENTATIONview looking at flame end of burners
BURNER
FLAME RETENTION RING
UPPER BURNERMOUNTING RAIL
LOWER BURNERMOUNTING RAIL
MANIFOLD ORIFICE
Right Left
Top
Bottom
FLAME SENSOR(SOME UNITS MAY HAVESENSOR LOCATED INMIDDLE OF BURNER)
SPARK ELECTRODEGROUND
1/8�(+1/64�)
FIGURE 16
SPARK ELECTRODE TO BURNER GAP
BURNER
FLAMESENSOR
SIDE VIEW END VIEW
1/4 in. 7 mmp 1/32 in. 0.79
mm
3/16 in.4.7 mm
11/16 in. 18 mmp 1/32 in. 0.79
mm
H--Gas ValveThe G24M uses a gas valvemanufactured by Honey-well (figure 17) orWhite Rodgers (figure 18). The valveis internally redundant to assure safety shut--off. If thegas valvemust be replaced, the same type valvemustbe 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 figure 17 or 18 for location of valve features.
An LPG changeover kit is available from Lennox. The kit
includes burner orifices and a regulator conversion kit.
I--Combustion Air Blower Prove(Pressure) Switch (S64)
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
means of a flexible silicone hose. It monitors air pres-
sure in the combustion air blower housing.
FIGURE 17
TYPICAL ACCESS TO REGULATOR
FOR ADJUSTMENT AND L.P. CHANGEOVER
21
2))
(Honeywell VR8205 series gas valve shown)
*$6 9$/9( 6+2:1 ,1 2)) 326,7,21
,1/(735(6685(
7$3
&$3 6&5(:�%ODFN�
$'-867,1* 6&5(:�:KLWH�
635,1*7DSHUHG (QG
'RZQ�5HG�
*$6 ,1/(7
35(6685(5(*8/$725
287/(735(6685(
7$3
,1/(735(6685(
7$3
FIGURE 18
WHITE RODGERS
36E GAS VALVEGAS VALVEKNOB SHOWNIN OFF POSITION
REGULATORCOVER SCREW
35(6685(7$3
35(6685(7$3
GAS INLET
Page 16
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-
tion if the combustion air blower is not operating.
FIGURE 19
PROVE SWITCH
COMBUSTION AIR BLOWERPROVE SWITCHNormally Open
Closes on Negative Pressure
PROVESWITCH
Sensing TubeAttaches to TopSide Of Blower
Top
Bottom
Left
RightBack
Front
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 switch setting (negative) w.c.
The pressure sensed by the switch is relative to atmo-
spheric pressure. If the flue becomes obstructed dur-
ing operation, the switch senses a loss of negative
pressure (pressure becomes more equal with atmo-
spheric pressure) and opens the circuit to the furnace
control and gas valve. The switch trip pressure is dif-
ferent dependingonunitmodel number. The trip pres-
sure is printed on the side of the limit.
The switch is factory set and is not field adjustable. It is
a safety shut-downcontrol in the furnace andmustnot
be bypassed for any reason.
II--PLACEMENT AND INSTALLATION
Make sure unit is installed in accordancewith installa-
tion instructions and applicable codes.
III--START-UP
A--Preliminary and Seasonal Checks1 -- 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 -- Set thermostat to OFF position. Close manual
knob on gas valve.
2 -- Wait 5 minutes.
3 -- Open manual knob on gas valve, replace burner
access door and turn on unit electrical supply.
WARNINGShock and burn hazard.
G24Munits are equippedwith either a direct sparkor hot surface ignition system. Do not attempt tolight manually.
4 -- Set fan switch to AUTO or ON and move system
selection switch to HEAT. Adjust thermostat to a
setting above room temperature.
5 -- If unit does not light the first time, the SureLight
control will attempt four more ignitions, the Ram
control will attempt two more ignitions before
locking out.
6 -- If lockout occurs, repeat steps 1, 2, 3 and 4.
C--Safety or Emergency Shutdown
Turn off unit power. Close manual andmain gas valves.
IMPORTANTIn case emergency shutdown is required, turn offthe main shut-off valve and disconnect the mainpower to unit. These controls should be properlylabeled by the installer.
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.
Page 17
IV--HEATING SYSTEM SERVICE CHECKS
A--A.G.A./C.G.A. Certification
All units are A.G.A. design certified without modifica-
tions. Refer to the G24M Operation and Installation
Instruction Manual for Information.
B--Gas Piping
Gas supplypiping shouldnot allowmore than0.5�W.C.
drop in pressure between gas meter and unit. Supply
gas pipemust not be smaller than unit gas connection.
Compounds used on gas piping threaded joints
should be resistant to action of liquefied petroleum
gases.
C--Testing Gas Piping
Whenpressure testinggas lines, thegas valvemustbe
disconnected and isolated. Gas valves can be dam-
aged if subjected tomore than 0.5psig (14�W.C.). See
figure 20. If thepressure is equal to or less than0.5psig
(14�W.C.), use the manual shut--off valve before pres-
sure testing to isolate furnace from gas supply.
FIGURE 20
MANUAL MAIN SHUT--OFF VALVE
WILL NOT HOLD TEST PRESSURE
IN EXCESS OF 0.5 PSIG (14�W.C.)
GAS VALVECAP
GAS PIPING TEST PROCEDURE
FIELD PROVIDED
LINE PRESSURE TAP
When checking piping connections for gas leaks, use
preferred means. Kitchen detergents can cause harmful
corrosion on variousmetals used in gas piping. Use of a
specialtyGas 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 PressureWhen testing supply gas pressure, connect test gauge
to inlet pressure tap (field provided). See figure 20.
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 dam-
age to gas valve or overfire. For natural gas units, op-
erating pressure at unit gas connection must be be-
tween 5.0� W.C. and 13.0� W.C. For L.P. gas units,
operating pressure at unit gas connectionmust be be-
tween 10.0� W.C. and 13.0� W.C.
On multiple unit installations, each unit should be
checked separately,with andwithout other units oper-
ating. Supply pressure must fall within range listed in
previous paragraph.
E--Check Manifold PressureAfter line pressure has been checked and adjusted,
checkmanifold pressure.Movepressuregauge toout-
let pressure tap located on unit gas valve (GV1).
Checks of manifold pressure aremade as verification of
proper regulator adjustment. Manifold pressure for the
G24M 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/pro-
pane gas the correct manifold pressure is 9.5 in. w.c.
IMPORTANTFor safety, connect a shut-off valve between themanometer and the gas tap to permit shut off ofgas pressure to the manometer.
Operating Pressure (outlet) in. W.C.
TABLE 9GAS VALVE REGULATION
3.5 +0 --0.3Natural
L.P. 9.5 + 0.5
Unit (Fuel)
The gas valve is factory set and should not require ad-
justment. All gas valves are factory regulated. See
table 9.
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
shouldburnmostly bluewith someorange streaks.
3 -- After allowing unit to stabilize for 5 minutes, re-
cord manifold pressure and compare to values
given in table 9.
NOTE--Shut unit off and remove manometer as
soon as an accurate reading has been obtained.
Take care to replace pressure tap plug.
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Page 21
To clean burners:
1 -- Turn off both electrical and gas power supplies to
furnace.
2 -- Disconnect gas supply piping and remove gas
manifold.
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
burners are properly seated in slots on tray andori-
fice in manifold.
8 -- Reinstall burner boxandgas supply piping. Recon-
nect 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.
CAUTIONPotential for gas leaks, fire or explosion.Some soaps used for leak detection are corrosiveto certain metals. Carefully clean piping thor-oughly after leak detection has been completed.Can cause damage to piping resulting in gasleaks, fire or explosion.
C--Supply Air Blower1 -- Check and clean blower wheel.
2 -- Motors used on the Lennox G24M series units
are permanently lubricated and need no further
lubrication.
D--Flue and Chimney
Flue must conform to all AGA/GAMA venting require-
ments. Flue pipe deteriorates from the inside out and
must be disconnected in order to check thoroughly.
Check flue pipe, chimney and all connections for tight-
ness 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.
FIGURE 24
HEAT EXCHANGER REMOVAL (unit shown in horizontal position)
REMOVE SCREWS (4)
SLIDE ENTIRE ASSEMBLY OUT OF CABINET
Front
Right
TopBottom
Left
Back
3DJH ��
VII--WIRING, OPERATION SEQUENCE
&TROUBLESHOOTING
A--Field Wiring, Thermostat Connections
),*85( ��
* :< &5
685(/,*+7 &21752/
7+(50267$7*$6
9$/9(
6(&21'$5<
/,0,76
%/$&.
72 &2035(6625
&217$&725
),(/' ,167$//(' &/$66 ,, ��9
),(/' ,167$//(' /,1( 92/7$*(
7<3,&$/ *��0 ),(/' :,5,1* ',$*5$0/� 1
�)851,6+('%<,167$//(5�
75$16)250(5
'225
,17(5/2&.
6:,7&+
&20%867,21
$,5 %/2:(535(6685( 6:,7&+
*1'
:+,7(
*: 5 <
35,0$5< /,0,7
)/$0( 52//287 6:,7&+(6
),*85( ��
COMPRESSOR
COMMON
POWER
HEAT
INDOOR BLOWER
COMMON
HS UNIT
COMMON
HS UNIT
COMPRESSOR
Y
W
G24MFurnace
Condensing UnitThermostat
G24M and CONDENSING UNITTHERMOSTAT DESIGNATIONS
(Refer to specific thermostat and outdoor unit.)
COOLINGY
G
W
C
R
G
R
C
3DJH ��
B--Early Model G24M Series With Ram Ignition Control
�
�
�
�
�
�
�
�
1 --Whendisconnect is closed, 120V is routed throughdoor interlock switch (S51) to feed the line voltagesideof the furnace control (A3) and transformerT1primary. Door interlock switch must be closed forA3 and T1 to receive voltage.
2 -- T1 supplies 24VAC to terminal �24VAC� on A3. Inturn, terminal �R� of A3 supplies 24VAC to termi-nal �RC� of the indoor thermostat (not shown).
3 --When there is a call for heat, W1 of the thermostatenergizes W of the furnace control with 24VAC.
4 -- CMB BLWR of the blower control energizes thecombustion air blower (B6).When the combustionair blower nears full speed, combustion air proveswitch (S18) closes.
5 --When S18 closes, assuming the flame rolloutswitch (S47), primary limit (S10) and secondary
limits (S21) are closed, the furnace control beginsa 45 second time-delay (pre-purge).
6 -- At the end of the pre-purge cycle, the furnace con-trol simultaneously opens thegas valve and sendshigh voltage to the spark electrode.
7 --When flame is sensed, the furnace control beginsa 45 second delay before energizing the indoorblower.
8 -- When heat demand is satisfied,W1 of the thermo-stat de-energizes W of the furnace control and thefurnace control immediately de-energizes the gasvalve. The combustion air blower runs for 5 se-conds (post-purge) before being de-energized.Also, the indoor blower runs for a designated peri-od (90--240 seconds) as set by switches on furnacecontrol.
3DJH ��
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?
CONTROL SELF--CHECK OKAY?
HI LIMIT SWITCH CLOSED?
PRESSURE SWITCH OPEN?
COMBUSTION AIR BLOWER ON?
PRESSURE SWITCH CLOSED?
PREPURGE (45 seconds)
IGNITION TRIAL (7 seconds) ---- START IGNITIONSPARK, OPEN MAIN GAS VALVE. INCREMENT
TRIAL REGISTER. HAS FLAME BEEN REGISTEREDWITHIN 7 SECONDS?
SYSTEM FAN ON.(Fixed 45--second delay)
FLAME SENSE OKAY?
FLAME CONTINUOUSLY CHECKED?
ROLLOUT SWITCHES CLOSED
HI LIMIT SWITCH CLOSED?
PRESSURE SWITCH CLOSED?
THERMOSTAT OPENS
LED: SLOW FLASH RATE
COMB. AIR BLOWER OFF (5 sec. delay)
FAN OFF (After selected 90, 120,180, or 240 delay)?
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
LOCKOUT: MAIN VALVE OFFCOMB. AIR AND SYSTEM FANS ON
RESET THERMOSTATLED: 5 flash if flame sensed with valve offLED: 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
CHECK TO SEE IF MAIN VALVE IS OFF.SEQUENCE HOLDS UNTIL PRES. SWITCH OPENS.
LED: 3 flashes.
CHECK TO SEE IF MAIN VALVE IS OFF.SEQUENCE HOLDS UNTIL PRES. SWITCH CLOSES.
LED: Fast flash rate.
MAIN VALVE AND SPARK ARE OFF.INCREMENT TRIAL REGISTERTHREE TRIALS COMPLETED?
NO
NO
NO
IGNITION RESET PERIODCOMBUSTION & SYSTEM FANS OFF.IS 60 MIN. RESET PERIOD COMPLETE?
LED: Fast flash rate.
MAIN VALVE AND SPARK OFF.
START IGNITION SPARK (IN 0.8 SEC. MAXIMUM).HAS FLAME BEEN DETECTED WITHIN 7 SEC.?
LOCKOUT. MAIN VALVE OFF.COMBUSTION AND SYSTEM FANS ON.RESET OR REPLACE ROLLOUT SWITCH.
LED: 4 flashes.
MAIN VALVE OFF. COMBUSTION & SYSTEM FANS ON.SEQUENCE HOLDS UNTIL SWITCH CLOSES.
LED: 4 flashes for hi limit.LED: 3 flashes for pressure switch.
SWITCH CLOSED
COMBUSTION FAN ON. SYSTEM FAN OFF.(AFTER DELAY TO OFF INTERVAL COMPLETED.)
LED: Fast flash rate.
NO
YES
YES
NO
NO
YES
NO
NO
NO
YES
3DJH ��
RAM CONTROL
COOLING TROUBLE SHOOTING SEQUENCE
YES
THERMOSTAT CALLS FOR COOLING.
LED: Slow flash rate.REMAINS UNCHANGED THROUGHOUT COOLING CYCLE.
NO
COMPRESSOR CONTACTOR AND SYSTEM FANENERGIZED AT COOLING SPEED AFTER
1 SECOND DELAY. ACC TERMINAL ENERGIZED.
THERMOSTAT OPENS.
COMPRESSOR OFF.
SYSTEM FAN AND ACC TERMINAL OFF AFTERCOMPLETING SELECTED DELAY INTERVAL
(At dip switches).
MANUAL FAN TROUBLESHOOTING SEQUENCE
MANUAL FAN SELECTION MADE AT THERMOSTAT.CONTROL ENERGIZES SYSTEM FAN AT CONTINUOUS
SPEED. ACC TERMINAL ENERGIZED.
THERMOSTAT CALLS FOR HEAT.
LED: Slow flash rate.REMAINS UNCHANGED THROUGHOUT SEQUENCE.
THERMOSTAT CALLS FOR COOLING.SYSTEM FAN SWITCHES TO HEATING SPEED AFTERSELECTED DELAY. ACC TERM. REMAINS ENERGIZED.
SYSTEM FAN SWITCHED TO COOLINGSPEED. ACC TERMINAL REMAINS ENERGIZED.
SYSTEM FAN SWITCHES TO CONTINUOUS SPEEDAND ENERGIZES ACC TERMINAL. BOTH REMAIN ON
UNTIL MANUAL FAN IS SWITCHED OFF AT THERMOSTAT.
YES NO
LED CODES
SLOW FLASH
FAST FLASH
2 FLASH
3 FLASH
4 FLASH
5 FLASH
STEADY ON
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.
.
THERMOSTAT OPENS.
THERMOSTAT OPENS.
SYSTEM FAN SWITCHED OFF AFTER DELAY.ACC TERMINAL DE--ENERGIZED.
Page 26
D-Late Model G24M Series With SureLight Ignition Control
TYPICAL G24M DIAGRAM(-11 MODEL SHOWN)
1 - When there is a call for heat, W1 of the thermostat ener-gizes 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 proveswitch closes (switch must close within 2-1/2 minutes orcontrol goes into 5 minute Watchguard Pressure Switchdelay). Once S18 closes, a 15-second pre-purge follows.
4 - SureLight control energizes ignitor. A 20-second warm-upperiod begins.
5 - Gas valve opens for a 4-second trial for ignition. Ignitorstays energized the first second of trial. (Board 97L48 only:ignitor energized during trial or until flame is sensed.
6 - Flame is sensed, gas valve remains open for the heat call.
7 - After 45-second delay, SureLight control energizes indoorblower B3.
8 - Whenheatdemand is satisfied,W1 of the indoor thermostatde-energizes W of the SureLight control which de-ener-gizes the gas valve. Combustion air blower B6 continues a5-second post-purge period, and indoor blower B3 com-pletes a selected OFF time delay.
3DJH ��
SURELIGHT CONTROL HEATING
SEQUENCE OF OPERATION
NORMAL HEATING MODE ABNORMAL HEATING MODE
CONTROL SELF--CHECK OKAY?
BURNER OFF?(CONTINUOUS FLAME CHECK)
NORMAL OPERATION:
LED #1 ---- SLOW FLASHLED #2 ---- SLOW FLASH
YES
YES
YES
GAS VALVE OFF. COMBUSTION AIR BLOWER OFF.INDOOR BLOWER DELAY OFF.
LED #1 ONLED #2 ON
(RESET CONTROL BY TURNING MAIN POWER OFF.)
POLARITY REVERSED.LED #1 ---- FAST FLASHLED #2 ---- SLOW FLASH
POWER ON
COMBUSTION AIR BLOWER ON FOR 1 SECOND.
TURN INDUCER ON FOR 1 SECOND.IS POLARITY REVERSED?
ROLLOUT SWITCH CLOSED?
THERMOSTAT CALLS FOR HEAT:
LED #1 ---- FAST FLASHLED #2 ---- FAST FLASH
IS COMBUSTION AIRPRESSURE SWITCH OPEN?
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 FLASHLED #2 ---- OFF
GAS VALVE OFF.COMBUSTION AIR BLOWER OFF.
INDOOR BLOWER OFF WITH DELAY.LED #1 OFF
LED #2 SLOW FLASH(Sequence holds until pressure switchcloses or thermostat resets control.)
NO
NO
YES
NO
IS THEREPROPER GROUND?
IS VOLTAGEABOVE 75 VOLTS?
LOW VOLTAGE SIGNAL AT LED HOLDSUNTIL VOLTAGE RISES ABOVE 75 VOLTS.
NOYESNO
SIGNAL IMPROPERGROUND AT LED.SIGNAL HOLDSUNTIL UNIT ISPROPERLYGROUNDED.
NO
NO
IS COMBUSTION AIR BLOWER ENERGIZED?(HTG ACC TERMINAL IS ENERGIZED WITH C.A.B.)
HAS COMBUSTION AIR PRESSURESWITCH CLOSED IN 2.5 MINUTES?
YES
YESPRESSURE 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?
NO
15-SECOND COMBUSTION AIR BLOWER PREPURGEINITIATED BY CLOSED PRESSURE SWITCH.
YES
YES
CONTINUED NEXT PAGE
YES
GAS VALVE OFF. COMBUSTION AIR BLOWER ON.INDOOR BLOWER ON.
LED #1 ALTERNATING FAST FLASHLED#2 ALTERNATING FAST FLASHCHECK FOR BROKEN IGNITOR OR
OPEN IGNITOR CIRCUIT
Page 28
NORMAL HEATING MODE ABNORMAL HEATING MODE
FLAME RECTIFICATION CURRENTCHECK. CAN FLAME BE PROVEN WITHIN4 SECONDS AFTER GAS VALVE OPENS?
(>0.15 microamps)
FLAME PRESENT?
INDOOR BLOWER ON DELAY BEGINS(45 seconds.)
PRIMARY AND SECONDARY LIMITSWITCHES CLOSED?
COMBUSTION AIR PRESSURESWITCH CLOSED?
LOW FLAME SIGNAL(Does not affect operation of control)
LED #1 -- SLOW FLASHLED #2 -- FAST FLASH
GAS VALVE DE-ENERGIZED.COMBUSTION AIR INDUCER
DE-ENERGIZED.INDOOR BLOWERON UNTIL SWITCH CLOSES.LED #1
-- SLOW FLASH. LED #2 -- ON.IS LIMIT SWITCH CLOSED?
GAS VALVE DE-ENERGIZED.COMBUSTION AIR INDUCER ON.
INDOOR BLOWER OFF WITH DELAYLED #1 -- OFF. LED #2 -- SLOW FLASH.
HAS CAB SWITCH CLOSED IN 2.5 MINUTES?
15-SECOND COMBUSTION AIR INDUCER PREPURGEINITIATED BY CLOSED PRESSURE SWITCH.
YES
IGNITOR WARM-UP -- 20 SECONDS.
YES
4-SECOND TRIAL FOR IGNITION. GAS VALVE OPENS.IGNITOR ENERGIZED FOR 1 SECOND AFTER VALVEOPENS. NO FLAME SENSED DURING THIS PERIOD.
BOARD 97L48: IGNITOR ENERGIZED DURING TRIAL ORUNTIL FLAME SENSED.
YESFLAME STABILIZATION PERIOD.
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.INDOOR BLOWER OFF.
HAS CONTROL FAILED TO SENSE FLAME FORFIVE CONSECUTIVE TRIES DURING A SINGLE
HEAT DEMAND?
IGNITION WATCHGUARD MODE. GAS VALVE OFF.COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF WITH DELAYLED 1 ALT. SLOW FLASH LED 2 ALT SLOW FLASH
IS 60-MINUTE RESET PERIOD COMPLETE?
YES
4 SECONDS
YES
HAS CONTROL RESET IGNITIONSEQUENCE FOUR TIMES?
FLAME SIGNAL ABOVE 0.7 MICROAMPS?YES
YES
HAS PRIMARY/SECONDARY LIMIT RESET.(See table 2 DIAGNOSTIC CODES for limit reset operation)
YES
ROLLOUT SWITCH CLOSED?
GAS VALVE POWER OFF.COMBUSTION AIR INDUCER POWER OFF.
INDOOR BLOWER OFF WITH DELAYLED #1 -- ON. LED #2 -- SLOW FLASH.
SEQUENCE HOLDS UNTIL ROLLOUT SWITCH IS RESET
YES
THERMOSTAT DEMAND SATISFIED.
LED #1 & #2 SIMULTANEOUS SLOW FLASHES.
YES
NO
5-MINUTE PRESSURE SWITCHWATCHGUARD MODE.
YES
IS THERE A PROPER GROUND?
IS VOLTAGE ABOVE 75 VOLTS?
IS IGNITOR INTACT AND CONNECTED?
LEDS SIGNALALTERNATINGFAST FLASH
NO YES
YESYES
YES
YES
NO
NO
NO
NO
NO
NO
NO
NOYES
YES
NO
NO
NO
NO
YES
YES
LIMIT SWITCH WATCH GUARDMODE. GAS VALVE OFF.COMB. AIR INDUCER OFF. IN-DOOR BLOWER OFF WITHDELAY. LED#1-SLOW FLASHLED#2- ON. IS 60MINUTE RE-SET PERIOD COMPLETE.?
YES
YES
COMB. AIR INDUCER CONTINUES 5-SECOND POST PURGEAFTER 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.
3DJH ��
SURELIGHT CONTROL COOLING SEQUENCE
NORMAL COOLING MODE ABNORMAL COOLING MODE
IGNITION CONTROL MAIN POWER ON.
CONTROL SELF DIAGNOSTIC CHECK.IS CONTROL OPERATING NORMALLY?
YES
SIGNAL POLARITY REVERSED AT LED.
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.
YES
TURN INDUCER ON FOR 1 SECOND.
IS POLARITY REVERSED?
ROLLOUT SWITCH MONITORED CONTINUOUSLY.IS ROLLOUT SWITCH CLOSED?
CHECK FOR MAIN BURNER FLAME SENSE.IS MAIN BURNER FLAME OFF?
LED: SLOW FLASH RATE REMAINS UNCHANGEDTHROUGHOUT COOLING CYCLE.
THERMOSTAT CALLS FOR COOLING.
COMPRESSOR CONTACTOR AND SYSTEM FANENERGIZED WITH 0-SECOND DELAY
ACB COOL SPEED AND ACC. TERM. ENERGIZED.
COMPRESSOR OFF.
THERMOSTAT OPENS.
ACB COOL SPEED AND ACC. TERM. OFFWITH 0-SECOND DELAY.
NO
YES
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.
NO
IS THEREPROPER GROUND?
IS VOLTAGEABOVE 75 VOLTS?
LOW VOLTAGE SIGNAL AT LET HOLDSUNTIL VOLTAGE RISES ABOVE 75 VOLTS.
NOYES
NO
SIGNAL IMPROPERGROUND AT LED.SIGNAL HOLDSUNTIL UNIT ISPROPERLYGROUNDED.
Page 30
CONTINUOUS LOW SPEED FAN SEQUENCE OF OPERATION
LED: SLOW FLASH RATE REMAINSUNCHANGED THROUGHOUT SEQUENCE.
MANUAL FAN SELECTION MADE AT THERMOSTAT.CONTROL (G) ENERGIZES SYSTEM FAN AT ACBLOW SPEED. ACC. TERMINAL IS ENERGIZED.
THERMOSTAT CALLS FOR HEAT (W).
THERMOSTAT CALLS FOR COOLING.
BOARD NO. 63K8901SYSTEM FAN DE-ENERGIZED. SYSTEM FANENERGIZES ON ACB HEAT SPEED AFTER
NORMAL DELAY.
THERMOSTAT OPENS. COMBUSTION AIRAND HTG ACC TERMINAL DE-ENERGIZE.
SYSTEM FAN SWITCHED TO ACB COOLSPEED. ACC. TERM. REMAINS ON.
THERMOSTAT OPENS.
BOARD 63K89: SYSTEM FAN OFF. ACC. TERM.OFF. (AFTER OFF DELAY COMPLETED).
MANUAL FAN SELECTION MADE AT THERMOSTAT.CONTROL (G) ENERGIZES SYSTEM FAN AT ACB
LOW SPEED. ACC. TERM. ENERGIZED.
NO YES
YES NO
HTG ACC. TERM. ENERGIZESWITH COMB. AIR BLOWER.
BOARD NO. 24L85, 56L83, 97L48SYSTEM FAN SWITCHES TO ACB HEAT SPEEDAFTER NORMAL DELAY (fan remains energized)
BOARDS 24L85, 56L83 AND 97L48:SYSTEM FAN SWITCHES TO
LOW SPEED AFTER NORMAL DELAY.(fan remains energized)
3DJH ��
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 Corrective Action / Comments
1.1
-- Both diagnostic lights fail to lightup.
1.1.1
Main voltage 120V not supplied tounit.
ACTION 1 -- Check 120V main voltage.Determine cause of main power failure.
LED#1--OffLED#2--Off
1.1.2
Miswiring of furnace or improperconnections.
ACTION 1 -- Check for correct wiring of 120Vto power make up box and transformer.ACTION 2 -- Check 24V wiring to controlboard.
1.1.3
Circuit breaker tripped or fails toclose.
ACTION 1 -- Replace circuit breaker if it is re-set but does not have continuity.ACTION 2 -- If circuit breaker still trips, checkfor short.
1.1.4
Door interlock switch failure.
ACTION 1 -- Check that door switch is activatedwhen door is closed.ACTION 2 -- Check wire connections to switch,replace loose connectors.ACTION 3 -- Check continuity of switch inclosed position. Replace if malfunctioning
1.1.5
Transformer Failure.
ACTION 1 -- Check that transformer output is24V. Replace if malfunctioning
1.1.6
Failed control board.
ACTION 1 -- If all the above items have beenchecked, replace board.
1.2
-- Diagnostic lights flash the roll--
out code.
1.2.1
Roll--out switch open.
ACTION 1 -- Manually reset the roll--outswitch by pushing the top button.ACTION 2 -- Determine the cause of the roll--out switch activation before leaving furnace.out code.
LED#1 O
1.2.2
Roll--out switch failure.
ACTION 1 -- Check continuity across roll--outswitch. Replace roll--out switch if switch isreset but does not have continuity.
LED#1--On,
LED#2--Slow Flash1.2.3
Mis iring or improper connectionsACTION 1 -- Check wiring connections toLED#2 Slow Flash
Miswiring or improper connectionsat roll--out switch.
ACTION 1 Check wiring connections toswitch.
1.2.4
Nine pin connector failure
ACTION 1 -- Check 9--pin connector for prop-er connection to control board.ACTION 2 -- Check continuity of the multiplug pin.
1.3
-- On initial power--up the comb. airblower does not energize.blower does not energize.-- Diagnostic lights flash the re-verse polarity code.
1.3.1
120V main power polarity re-versed.
ACTION 1 -- Check the 120V has line and neu-tral correctly input into control.ACTION 2 -- Reverse the line and neutral at the120V field connection.
LED#1--Fast Flash,LED#2--Slow Flash.
versed. 120V field connection.
1.4
-- On initial power up the combus-tion air blower does not energize.-- Diagnostic lights flash normalpower on operation
1.4.1
Open combustion air blowermotorcircuit.
ACTION 1 -- Check for 120V to combustion airblower. If no power, check wire and connec-tions.
power on operation.
LED#1--Slow FlashLED#2--Slow Flash
1.4.2
Failed combustion air blower mo-tor.
ACTION 1 -- If power is present at blower, re-place blower.
3DJH ��
PROBLEM 1: UNIT FAILS TO OPERATE IN THE COOLING, HEATING, OR CONTINUOUS FAN MODE
Condition Possible Cause Corrective Action / Comments
1.5
-- On initial power--up the combus-tion air blower remains energized.Di ti li ht fl h th i
1.5.1
Improper ground to the unit.
ACTION 1 -- Check that the unit is properlyground.ACTION 2 -- Install a proper main ground tothe unitg
-- Diagnostic lights flash the im-proper main ground.
1.5.2
6--Pin connector is improperly at-tached to the circuit board.
ACTION 1 --Check 6--pin connector for properinstallation. Correctly insert connector intocontrol.
LED#1--Alternating Fast FlashLED#2--Alternating Fast Flash
1.5.3
Line voltage is below 75V.
ACTION 1 -- Check that the line voltage isabove 75V. Determine cause of voltage dropand 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 combus-tion air blower remains energized.-- Diagnostic lights flash the improper main ground.Combustion air blower cycles 5
2.1.1
Open ignitor circuit.
ACTION 1 -- Check for correct wiring andloose connections in the ignitor circuit. Checkmult--plug connections for correct installa-tion.
-- Combustion air blower cycles 5seconds on 55 seconds off.
LED#1--Alternating Fast FlashLED#2--Alternating Fast Flash
2.1.2
Broken or failed ignitor.
ACTION 1 -- Unplug ignitor and read resis-tance across ignitor. If resistance does notreadbetween10.9and19.7ohms, replace theignitor.
PROBLEM 3: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER DOES
NOT ENERGIZE
Condition Possible Cause Corrective Action / Comments
3.1
-- Unit operates with a cooling orcontinuous fan demand.-- Combustion air blower will notstart with a Heating demand.-- Diagnostic lights flash the limitfailure mode
3.1.1
Primary or secondary (if equipped)limit open.
ACTION 1 -- Check continuity acrossswitch(es). Switches reset automaticallyupon cool down.ACTION 2 -- Check for restrictions on blowerinlet air (including filter) and outlet air. Deter-mine cause for limit activation before placingunit back in operation.
failure mode.
LED#1--Slow Flash,LED#2--On
3.1.2
Miswiring of furnace or improperconnections at limit switch(es).
ACTION 1 -- Check for correct wiring andloose connections. Correct wiring and/or re-place any loose connections.
3.2
-- Unit operates with a cooling andcontinuous fan demand.-- Combustion air blower will notstart with a Heating demand.-- Diagnostic lights flash the pres-sure switch failure code
3.2.1
Miswiring of furnace or improperconnections to combustion air
blower.
ACTION 1 -- Check for correct wiring andloose connections. Correct wiring and/or re-place any loose connections.
sure switch failure code.
LED#1--Off,LED#2--Slow Flash
3.2.2
Pressure switch stuck closed.
ACTION 1 -- Check that the pressure switch isopen without the combustion air blower op-erating. Replace if malfunctioning
3DJH ��
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 andcontinuous fan demand.-- Combustion air blower will notstart with a Heating demand.-- Diagnostic lights flash the pres-sure switch failure code 2.5minutes
3.3.1
Miswiring of furnace or improperconnections to combustion air
blower.
ACTION 1 -- Check for correct wiring andloose connections. Correct wiring and/or re-place any loose connections.
sure switch failure code 2.5minutesafter heating demand.
LED#1--Off,LED#2--Slow Flash
3.3.2
Combustion air blower failure.
ACTION 1 -- If there is 120V to combustion airblower and it does not operate, replace com-bustion 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 andcontinuous fan demand.-- Combustion air blower ener-gizes with a heating demand
4.1.1
Pressure switch does not closedue to incorrect routing of the
pressure switch lines.
ACTION 1 -- Check that the pressure switchlines are correctly routed. Correctly routepressure switch lines.
gizes with a heating demand.-- Diagnostic lights flash the pres-sure switch failure code 2.5 min-utes after heating demand.
4.1.2
Pressure switch does not closedue to obstructions in the pressure
lines.
ACTION 1 -- Remove any obstructions fromthe the pressure lines and/or taps.
LED#1--OffLED#2--Slow Flash
4.1.3
Pressure switch lines damaged
ACTION 1 -- Check pressure switch lines forleaks. Replace any broken lines.
LED#2 Slow Flash
4.1.4
Pressure switch does not closedue 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 instruc-
tions.
ACTION 4 -- Check voltage to thre combus-
tion air blower.
4.1.5
Wrong pressure switch installed inthe unit, or pressure switch is out
of calibration.
ACTION 1 -- Check that the proper pressureswitch is installed in the unit. Replace pres-sure switch if necessary.
4.1.6
Miswiring of furnace or improperconnections at pressure switch.
ACTION 1 -- Check for correct wiring andloose connections. Correct wiring and/or re-place any loose connections.
4.1.7
Pressure switch failure.
ACTION 1 -- If all the above modes of failurehave been checked, the pressure switch mayhave failed. Replace pressure switch and de-termine if unit will operate.
3DJH ��
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
-- Unit operates with a cooling and
continuous fan demand.
Combustion air blower ener
5.1.1
Check that gas is being supplied tothe unit.
ACTION 1 -- Check line pressure at the gasvalve.Pressure shouldnot exceed13�WC forboth natural and propane. Line pressureshould read a minimum 4.5� WC for naturaland 8.0�WC for propane.
-- Combustion air blower ener-
gizes with Heating demand.
-- Ignitor is energized but unit fails
to light.
5.1.2
Miswiring of gas valve or looseconnections at multi--pin control
amp plugs or valve.
ACTION 1 -- Check for correct wiring andloose connections. Correct wiring and/or re-place any loose connections.
LED#1--Alternating Slow Flash
LED#2--Alternating Slow Flash
5.1.3
Malfunctioning gas valve or igni-tion control.
ACTION 1 -- Check that 24V is supplied to thegas valve approximately 35 seconds afterheat demand is initiated.ACTION 2 -- Replace the valve if 24V is sup-plied but valve does not open (check for ex-cessive gas line pressure before replacinggas valve).ACTION 3 -- Replace the control board if 24Vis 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
-- Burners fire with a heating de-mand.-- Burners light but unit shuts offprior to satisfying T--stat demand.-- Diagnostic lights flash the pres-sure switch code.
LED#1--OffLED#2--Slow Flash
6.1.1
Low pressure differential at thepressure switch.
ACTION 1 -- Check for restricted vent inlet orexhaust. Remove all blockage.ACTION 2: Check for proper vent sizing. Seeinstallation instructions.
6.2
-- Combustion air blower energizeswith a heating demand.B li ht b t f il t t lit
6.2.1
Sensor or sense wire is improperlyinstalled.
ACTION 1 -- Check that sensor is properlylocated (page 10) and that the sense wire isproperly attached to both the sensor andthe control.
-- Burners light but fail to stay lit.-- After 5 tries the control diagnos-tics flash the watchguard burnersfailed to ignite code.
6.2.2
Sensor or sense wire is broken.
ACTION 1 -- Check for a broken sensor.ACTION 2 -- Test continuity across the sensewire. If wire or sensor are damaged replacethe component.failed to ignite code.
LED#1--Alternating Slow FlashLED#2--Alternating Slow Flash
6.2.3
Sensor or sensor wire is groundedto the unit.
ACTION 1 -- Check for resistance betweenthe sensor rod and the unit ground.ACTION 2 -- Check for resistance betweenthe sensor wire and the unit ground.ACTION 3 -- Correct any shorts found in cir-cuit.
6.2.4
Control does not sense flame.
ACTION 1 -- Check the microamp signalfrom the burner flame. If the microamp sig-nal is below 0.70 microamps, check thesense rod for proper location or contamina-tion.ACTION 2 -- Replace, clean, or relocateflame sense rod. If rod is to be cleaned, usesteel wool or replace sensor. DO NOTCLEAN ROD WITH SAND PAPER. SAND PA-PER WILL CONTRIBUTE TO THE CONTAMI-NATION PROBLEM. NOTE: Do not attemptto bend sense rod.
3DJH ��
PROBLEM 6: BURNERS LIGHT WITH HEATING DEMAND BUT UNIT SHUTS DOWN
PREMATURELY (CONT.)
Condition Possible Cause Corrective Action/Comments
6.3
-- Combustion air blower ener-gizes with a heating demand.-- Burners light.-- Roll--out switch trips during theheating demand.-- Diagnostic lights flash roll--outfailure.
6.3.1
Unit is firing above 100% of thenameplate input.
ACTION 1 -- Check that themanifold pressurematches value listed on nameplate. Seeinstallation instructions for proper proce-dure.ACTION 2 -- Verify that the installed orificesizematch the size listed on the nameplate orinstallation instructions.ACTION 3 -- Check gas valve sensing hose toinsure no leaks are present.ACTION 4 -- Check the input rate to verify ratematches value listed on nameplate.
LED#1--OnLED#2--Slow Flash
6.3.2
Gas orifices leak at the manifoldconnection.
ACTION1 --Tightenorifice until leak is sealed.NOTE: Be careful not to strip orifice threads.ACTION 2 -- Check for gas leakage at thethreaded orifice connection. Use approvedmethod for leak detection (see unit instruc-tions).
6.3.3
Insufficient flow through the heatexchanger caused by a sooted or
restricted heat exchanger.
ACTION1 --Check for sootingdeposits or oth-er restrictions in the heat exchanger assem-bly. Clean assembly as outlined in instructionmanual.ACTION 2 -- ForG24Mgas furnaces, check forproper combustion and flow. CO2 shouldmeasure between 6.0% and 8.0% for NG andbetween 6.5% and 8.5% for LP. CO shouldmeasure below .04% (400PPM) in an air--freesample of flue gases for either NG or LP.
6.3.4
Burners are not properly located inthe burner box.
ACTION 1 -- Check that the burners are firinginto the center of the heat exchanger open-ings. Correct the location of the burners ifnecessary.
6.4
-- Combustion air blower ener-gizes with a heating demand.-- Burners light roughly and theunit fails to stay lit.-- Diagnostic lights flash watch-guard flame failure.
6.4.1
Recirculation of flue gases. Thiscondition causes rough ignitionsand operation. Problem is charac-terized by nuisance flame failures.
ACTION 1 -- Check for proper flow of exhaustgases away from intake vent. Remove anyobstacles in front of the intake and exhaustvent which would cause recirculation.ACTION 2 -- Check for correct intake and ex-haust vent installation. See instructions
guard flame failure.
LED#1--Alternating Slow FlashLED#2--Alternating Slow Flash
6.4.2
Improper burner cross--overs
ACTION 1 -- Remove burner and inspect thecross--overs for burrs, or any restriction or ifcrossover is warped. Remove restriction orreplace burners.
3DJH ��
PROBLEM 6: BURNERS LIGHT WITH HEATING DEMAND BUT UNIT SHUTS DOWN
PREMATURELY (CONT.)
6.5
-- Combustion air blower ener-gizes with a heating demand.-- Burners light.-- Diagnostic lights flash watchguard flame failure.-- NOTE� Unit might go into 60minute Watchguard mode depend-ing on intermittent nature of sen-sor signal.
LED#1--Alternating Slow FlashLED#2--Alternating Slow Flash
6.5.1
Loose sensor wire connectioncauses intermittent loss of flame
signal.
ACTION 1 -- Check that the sensor is properlylocated.ACTION2 --Check that the sense wire is prop-erly attached to both the sensor and the con-trol. Pay extra attention to the pin connectors.
PROBLEM 7: CONTROL SIGNALS LOW FLAME SENSE DURING HEATING MODE
Condition Possible Cause Corrective Action/Comments
7.0
-- Unit operates correctly but thediagnostic lights flash low flamesense code
7.1.1
Sense rod is improperly located onthe burner.
ACTION 1 -- Check the sense rod for properlocation on the burner. Properly locate thesense rod or replace if rod cannot be locatedcorrectly.
sense code.
LED#1--Slow FlashLED#2--Fast Flash
7.1.2
Sense rod is contaminated.
ACTION 1 -- Check sense rod for contamina-tion or coated surface. Clean the sense rodwith steel wool or replace sensor. DO NOTUSE SAND PAPER TO CLEAN ROD. SANDPAPER WILL CONTRIBUTE TO THE CON-TAMINATION PROBLEM.
PROBLEM 8: INDOOR BLOWER FAILS TO OPERATE IN COOLING, HEATING, OR CONTINUOUS
FAN MODE
Condition Possible Cause Corrective Action/Comments
8.0
-- Indoor blower fails to operate incontinuous fan, cooling, or heatingmode.
8.1.1
Miswiring of furnace or improperconnections at control or indoor
blower motor.
ACTION 1-- Correct wiring and/or replace anyloose connections. Check for correct wiringand loose connections.
8.1.2
120V is not being supplied to theindoor air blower or blower motor
failure.
ACTION 1 -- Check for 120V at the variouscalls for indoor blower by energizing �Y�,�G�, and �W� individually on the low voltageterminal strip. Note that when �W� is ener-gized, the blower is delayed 45 seconds. Ifthere is 120V to eachmotor tap but the blow-er 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 operationACTION 1 -- Call Technical Support, Dallas.