svc g24m 1297 - Heating and Air Parts: Lennox OEM … SERVICE.pdf · Page 1 ª 1998 Lennox Industries Inc. Litho U.S.A. Corp. 9723-L12 G24M Service Literature Revised 07-2001 G24M

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)



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 (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


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


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


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?


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.)


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


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


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.


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


SEQUENCE HOLDS UNTIL ROLLOUT SWITCH CLOSES.

NO


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).


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


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.


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


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.


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.


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.


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.


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.)


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.


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


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.)


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.


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.


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


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


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


9.0

-- AM radio interference.

9.1.2

Ignitor operationACTION 1 -- Call Technical Support, Dallas.

Documents

svc g24m 1297 - Heating and Air Parts: Lennox OEM … SERVICE.pdf · Page 1 ª 1998 Lennox Industries Inc. Litho U.S.A. Corp. 9723-L12 G24M Service Literature Revised 07-2001 G24M