Lennox G24M User Manual

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G24M

Blowerwheelnomina

diameterxwidt

Nominalcoolin

thatcanbeadde

Down-flow

Corp. 9723-L12

Service Literature

G24M SERIES UNITS

G24Mseriesunitsaremid-efficiencygasfurnacesmanufactured with tubular steel heat exchangers formed of aluminizedsteel.G24Munitsareavailableinheatingcapacitiesof 45,000 to 140,000 Btuh and cooling applications up to 5 tons. Refer to Engineering Handbook for proper sizing.

Units are factory equipped for use with natural gas. A kit is availableforconversiontoLPGoperation.EarlymodelG24M units use electronic (direct spark) ignition. Late model G24M model units feature the Lennox SureLightT silicon-nitride ignition system. The G24MX unit meets the California Nitrogen Oxides (NOx) Standards and California Seasonal Efficiency requirements. All units use a redundant gas valve to assure safety shut-off as required by A.G.A. or C.G.A.

Unitsmaybeinstalledinupflow,downfloworhorizontalposition. The heat exchanger is designed for upright or horizontal use only. When the unit is installed in the downflow position,theheatexchangerisfieldremovedandreinstalled so it isuprightwhen the cabinet is inverted.Nofield conversion is required when the unit is installed in the horizontal position.

The heat exchanger, burners and manifold assembly can easily be removed for inspection and service by simply disconnecting gas, unplugging wiring harness and spark wires and removing four screws holding the heat exchanger in place. Then the heat exchanger slides out of the cabinet.

Model 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)

in. 9 x 7 10 x 7 9 x 7 10 x 7

Blower motor output — hp (W) 1/4 (187) 1/3 (224) 1/4 (187) 1/3 (224)

Shipping weight — lbs. (kg) 1 package 130 (59) 135 (61) Electrical characteristics 120 volts — 60 hertz — 1 phase (less than 12 amps) All models

LPG/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)

Catalog No.

Filter Kit

Down-flow Combustible Floor Base Sidewall Power Venting Kit 79J15 — 25 lbs. (11 kg) Hanging Bracket Kit

lAnnual Fuel Utilization Efficiency based on U.S. DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherized

furnaces.

}Polyurethane frame type filter isfurnished with kit. ¡Filters arenot furnished with kitand must be ordered extra.

No. & Size of Filters — in. (mm)

mm 229 x 178 254 x 178 229 x 178 254 x 178 Tons 1, 1-1/2 or 2 2, 2-1/2 or 3 1, 1-1/2 or 2 2, 2-1/2 or 3

kW 3.5, 5.3 or 7.0 7.0, 8.8 or 10.6 3.5, 5.3 or7.0 7.0, 8.8 or 10.6

b Optional Accessories (Must Be Ordered Extra) b

Revised 07-2001

All specifications in this manual are subject to change. Procedures outlined in this manual are presented as a recommendation only and do not supersede or replace local or state codes. In the absence of local or state codes, the guidelines and procedures outlined in this manual (except where noted) are recommended only and do not constitute code.

SPECIFICATIONS

LB-69843A (32J01) — 3 lbs. (1 kg)

LB-79239A (67J91) — 10 lbs. (4 kg)

LB-69957 (46J66) — 15 lbs. (8 kg)

Single (32J02) TenPack (66K64)

(1) 16 x 20 x 1 (406 x 508 x 25)

(2) 16 x 20 x 1 (406 x 508 x 25)

Page 1

ã 1998 Lennox Industries Inc.

Litho U.S.A.

SPECIFICATIONS

Nominal

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)

A.F.U.E. 80.0% 80.1% 80.0%

California Seasonal Efficiency 76.3% 76.5% 77.0%

Flue size connection diameter  in. (mm) round 4 (102)

Temperature rise range 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)

ower wheelnomina

diameter x width

in. 12 x 8 12 x 9

mm 305 x 203 305 x 229

Blower motor output  hp (W) 1/2 (373) 3/4 (560)

that can be added

cooling

Tons 2, 2-1/2, 3, 3-1/2 or 4 3-1/2, 4, 5 or 6

kW 7.0, 8.8, 10.6, 12.3 or 14.1 12.3, 14.1, 17.6 or 21.1

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

Optional Accessories (Must Be Ordered Extra)

LPG/propane kit LB-69845L

Twinning Kit

Up--Flow/Horizontal Filter and Filter Rack Kits

No. & size of filters -- in. (mm)

Single (

32J02

) Ten Pack (

(1) 16 x 20 x 1 (406 x 508 x 25)

(38K84)

66K64

96J69

)

LB-69845K

 5 lbs. (2 kg)

Single

(46J14)

Ten Pack

(1) 20 x 20 x 1 (508 x 508 x 25)

(81J14)

(66K65)

Catalog No. LB-69843A

Down-flow Filter Kit

Down-flow Combustible floor Base LB-79239A

Sidewall Power Venting Kit

Hanging Bracket Kit LB-69957

Annual Fuel Utilization Efficiency based on U.S. DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherized furnaces.

Polyurethane frame type filter is furnished with kit.

Filters are not furnished with kit and must be ordered extra.

No. & Size of Filters  in. (mm)

(2) 16 x 20 x 1 (406 x 508 x 25)

10lbs.(4kg) LB-79239B

(67J91)

79J15

(46J66)

3DJH 

 3 lbs. (1 kg)

(32J01)

 25 lbs. (11 kg)

 15 lbs. (8 kg)

(67J92)

 10 lbs. (4 kg)

SPECIFICATIONS

Blower wheel nominal

Nominal cooling

No.& Size

External Static

Model No.

Input Btuh (kW) Output Btuh (kW)

A.F.U.E.

California Seasonal Efficiency

Flue size connection diameter  in. (mm) round Temperature rise range EF(EC) High static certified by A.G.A./C.G.A.  in wg. (Pa) Gas Piping Size I.P.S. Natural or LPG/propane -- in (mm)

Blower wheel nominal

diameter x width

in. mm

Blower motor output  hp (W)

Nominal coolin

that can be added

Tons 2, 2-1/2, 3, 3-1/2 or 4

kW 7.0, 8.8, 10.6, 12.3 or 14.1 Shipping weight  lbs. (kg) 1 package Electrical characteristics

Optional Accessories (Must Be Ordered Extra)

LPG/propane kit Twinning Kit Up--Flow/Horizontal Filter and Filter Rack Kits

No. and size of filters -- in. (mm)

Catalog No.

Down-flow

Filter Rack

No. & Size of Filters

in.

Down-flow Combustible Floor Base Sidewall Power Venting Kit

Hanging Bracket Kit

Annual Fuel Utilization Efficiency based on U.S. DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherized

furnaces.

Polyurethane frame type filter is furnished with kit.

2 in. x 5 in. (51 mm x127 mm) flue adaptor furnished with -140 input furnaces for connection to furnace induced draft blower.

Filters are not furnished with kit and must be ordered extra.

G24M3/4-120 G24M4/5(X)-120

120,000 (35.2)

98,400 (28.8)

80.0% 80.1%

Not Available 75.5%

4 (102) 5 (127)

45 - 75 (25 - 42)

.50 (125) .65 (162)

1/2 (13)

12 x 8 12x9

305 x 203 305 x 229

1/2 (373) 3/4 (560)

3-1/2, 4, 5 or 6

12.3, 14.1, 17.6 or 21.1

175 (79)

120 volts  60 hertz  1 phase (less than 12 amps) All models

Single

(46J14)

Ten Pack

LB-69845K

96J69

(66K65)

(81J14)

 5 lbs. (2 kg)

(1) 20 x 20 x 1 (508 x 508 x 25)

LB-69843A

(32J01)

 3 lbs. (1 kg)

(1) 20 x 20 x 1 (508 x 508 x 25)

(2)16x20x1

(2) 406 x 508 x 25

LB-79239B

(67J92)

 10 lbs. (4 kg)

 25 lbs. (11 kg)

79J15

LB-69957

(46J66)

 15 lbs. (8 kg)

G24M4/5-140

140,000 (41.0) 114,800 (33.6)

80.0%

Not Available

190 (86)

Single

(58J93)

(66K66)

LB-79239C

 12 lbs. (5 kg)

Ten Pack

(67J93)

BLOWER DATA

G24M2-45, G24M2-60 AND G24M2-75 BLOW

ER PERFORMANCE

External Static

Pressure

High Medium-High Medium-Low Low

Air Volume at Various Blower Speeds

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

External Static

G24M3-60 AND G24M3-75 BLOWER PERFORMANCE

Air Volume at Various Blower Speeds

Pressure

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

High Medium-High Medium-Low Low

G24M4-75, G24M3/4-100 AND G24M3/4-120 BLOWER PERFORMANCE

External Static

Pressure

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

High Medium-High Medium Medium-Low Low

Air Volume at Various Blower Speeds

3DJH 

BLOWER DATA

External Static

G24M4/5-100, G24M4/5-120 AND G24M4/5-140 BLOWER PERFORMANCE

External Static

Pressure

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

High Medium-High Medium Medium-Low Low

Air Volume at Various Blower Speeds

FILTER AIR RESISTANCE

cfm (L/s) in. w.g. (Pa)

0 (0) 0.00 (0)

200 (95) 0.01 (2)

400 (185) 0.03 (7)

600 (280) 0.04 (10)

800 (375) 0.06 (15)

1000 (470) 0.09 (22)

1200 (560) 0.12 (30)

1400 (655) 0.15 (37)

1600 (750) 0.19 (47)

1800 (845) 0.23 (57)

2000 (935) 0.27 (67)

2200 (1030) 0.33 (82)

2400 (1125) 0.38 (95)

2600 (1220) 0.44 (110)

3DJH 

G24M

PARTS IDENTIFICATION

COMBUSTION AIR

BLOWER

FRONT LOUVERED

PANEL

TRANSFORMER

HEAT EXCHANGER

FLUE BOX

PRESSURE

SWITCH

PRIMARY

LIMIT

LOW PRESSURE SWITCH

(Propane Only)

BURNER

ASSEMBLY

VENT ADAPTER

ASSEMBLY

NOx

TURBULATOR

SECONDARY

LIMITS

CABINET TOP

G24M

CABINET

CABINET BOTTOM

ROLLOUT SWITCH (2)

COMBUSTION AIR

PROVE SWITCH

ORIFICES

MANIFOLD

BURNERS

CONTROL

BOARD

DOOR INTERLOCK SWITCH

FIGURE 1

HEATING COMPONENTS (shown in horizonta

BLOWER ASSEMBLY

l position)

PRIMARY LIMIT

Bottom

Front

Left

Back

Top

GAS VALVE

COLLECTOR

FIGURE 2

Page 6

Right

HEAT EXCHANGER

COMBUSTION AIR BLOWER

(shown in upflow position with SureLight ignition system)

G24M BURNER ASSEMBLY

BURNER BOX

TOP

UPPER

BURNER

MOUNTING

RAIL

LOWER

BURNER

MOUNTING

RAIL

FLAME

SENSOR

ORIFICE

MANIFOLD

SURELIGHT

IGNITOR

ROLLOUT

SWITCHES

BURNER

VEST PANEL

GAS VALVE

BURNER BOX

PRIMARY LIMIT

Left

Front

HEAT EXCHANGER

Top

Back

Right

Bottom

FIGURE 3

G24M BLOWER DOOR COMPONENTS -- BLOWER ACCESS

To Access Blower:

J135/

P135

J1/P1

1-- Turn off power to unit and disconnect L1

and 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 limit

control. 5-- Disconnect J43 from blower motor. 6-- Remove blower panel and lift from unit.

Top

Back

Right

Left

Front

Bottom

FIGURE 4

Page 7

I-UNIT COMPONENTS (Figures 1, 2, 3)

G24M unit components are shown in figure 1. The blower controls, gas valve and burners can be accessed by reĆ moving the front access panel. A separate blower access door is located behind the front access panel. Electrical control components are mounted to the blower access door.

G24M units are factory equipped with bottom return air panels in place. The panels are designed to be field removed as reĆ quired for bottom air return. Indentations on side of units, show where side return opening should be cut during installaĆ tion.

A-Blower Door Components (Figure 4)

Electrical burner control and blower control components are located on the outside surface of the blower access door. Jackplugs allow the blower door to be easily reĆ moved for blower service.

Located on the blower door are the unit transformer (T1), the furnace control (A3) and door interlock switch (S51). Furnace control (A3) combines the function of a burner ignition control and blower control.

1- Control Transformer (T1)

A transformer located on the blower door provides power to the low voltage section of the unit. Transformers on all models are rated 30VA with a 120V primary and a 24V secĆ ondary.

2-Door Interlock Switch (S51)

A door interlock switch rated 16A at 125VAC is located on the blower access door. The switch is wired in series with line voltage. When the blower door is removed the unit will shut down.

DANGER

Shock hazard.

Disconnect power before servicing. Control is not field repairable. If control is inoperable, simply replace entire control.

Can cause injury or death. Unsafe operation will result if repair is attempted.

3- SureLight Ignition System (A3)

Late Model G24M Units

Late model G24M units are equipped with the Lennox SureLight ignition system. The system consists of ignitor (f igur e 5) and ignition control board (f igur e 6 wit h control terminal designations in table 1). The board and ignitor work in combination to ensure furnace ignition and ignitor durability. The SureLight integrated board controls all major furnace operations. The board also features two LED lights for troubleshooting and two accessory termiĆ nals rated at (4) four amps. See table 2 for troubleshootĆ ing diagnostic codes. Table 3 and 4 show jack plug termiĆ nal designations. Units equipped with the SureLight board can be used with either electronic or electro-meĆ chanical thermostats without modification. The SurĆ eLight ignitor is made of durable silicon-nitride. Ignitor longevity is also enhanced by voltage ramping by the control board. The board finds the lowest ignitor temperaĆ ture which will successfully light the burner, thus increasĆ ing the life of the ignitor.

a-flame sensor

The flame sensor uses flame rectification to sense comĆ bustion. During operation, flame is sensed by current passed through the flame and sensing electrode. Figure 7 shows the gap between tip of the electrode and the burner surface.

SURELIGHT IGNITOR

UPPER BURNER MOUNTING RAIL

SURELIGHT IGNITOR BURNER ASSEMBLY

FLAME RETENTION RING

FIGURE 5

Page 8

ORIFICE

FLAME SENSOR

SURELIGHT CONTROL BOARD

LATE MODEL G24M UNITS

TABLE 1

SURELIGHT CONTROL TERMINAL DESIGNATIONS

ACB COOL ACB HEAT PARK ACB LOW ACC TX HOT HTG ACC NEUTRALS 24VACHOT 24VACRTN FLAME SENSE

Blower - Cooling Speed (Line Volt) Blower - Heating Speed (Line Volt) Alternate Blower Speeds (Dead) Continuous Low Speed Blower Accessory Terminal (Line Volt) 120VACHot to Transformer 120VACHot Input Heat Only Accessory (Line Volt) 120VACNeutrals 24VACHot from Transformer 24VACReturn from Transformer Flame Sense Terminal

NORMAL FLAME SIGNAL > 0.7 MICROAMPS LOW FLAME SIGNAL < 0.7 MICROAMPS MINIMUM FLAME SIGNAL < 0.15 MICROAMPS

FLAME SENSOR TO BURNER GAP

1/4 in. 7 mm

¦ 1/32 in. 0.79

BURNER

SIDE VIEW END VIEW

FIGURE 6

TABLE 2

DIAGNOSTIC CODES

MAKE SURE TO ID LED’S CORRECTLY: REFER TO INSTALLATION INSTRUCTIONS FOR CONTROL BOARD LAYOUT.

LED #1 LED #2 DESCRIPTION

SIMULTANEOUS

SLOW FLASH

SIMULTANEOUS FAST

FLASH

SLOW FLASH ON

OFF SLOW FLASH

ALTERNATING SLOW

FLASH

SLOW FLASH OFF

ON SLOW FLASH ON

OFF

FAST FLASH SLOW FLASH

SLOW FLASH FAST FLASH

ALTERNATING FAST

FLASH

SIMULTANEOUS

SLOW FLASH

SIMULTANEOUS FAST

ALTERNATING SLOW

ALTERNATING FAST

FLASH

OFF

FLASH

Also signaled during cooling and continues fan.

Normal operation - signaled when heating demand initiated at thermostat.

Primary or Secondary limit open. Units with board 63K8901 or 24L85: Limit must

close within 5 trials for ignition or board goes into one hour limit Watchguard.

Units with board 56L83 or 97L48: Limit must close within 3 minutes or board

Pressure switch open or has opened 5 times during a single call for heat; OR:

Blocked inlet/exhaust vent; OR: Condensate line blocked; OR: Pressure switch

closed prior to activation of combustion air blower.

Flame sensed without gas valve energized.

Rollout switch open. OR: 9 pin connector improperly attached.

Circuit board failure or control wired incorrectly.

Main power polarity reversed. Switch line and neutral.

Low flame signal. Measures below .7 microAmps. Replace flame sense rod.

Improper main ground or line voltage below 75 volts; OR: Broken ignitor; OR:

Power - Normal operation

goes into one hour limit Watchguard.

Watchguard - burners fail to ignite.

Open ignitor circuit.

3/16 in.

4.7 mm

FLAME

SENSOR

FIGURE 7

11/16in. 18 mm

¦ 1/32 in. 0.79

NOTE - Slowflash equals1 Hz (oneflash persecond). Fast flashequals 3Hz (threeflashes per second).Drop outflame sense current< 0.15microAmps

Page 9

TABLE 3

SureLight BOARD J156 (J2) TERMINAL

PIN # FUNCTION

1 Ignitor

2 3 4 5 6

DESIGNATIONS

Not Used

Ignitor Neutral

Combustion Air Blower Line Voltage

Not Used

Combustion Air Blower Neutral

TABLE 4

SureLight BOARD J58 (J1) TERMINAL

PIN # FUNCTION

1 Primary Limit In

2 3 4 5 6 7 8 9

DESIGNATIONS

Gas Valve Common Roll Out Switch Out

Gas Valve 24V

Pressure Switch In

Pressure Switch and Primary Limit Out

Not Used

Roll Out Switch In

Ground

ELECTROSTATIC DISCHARGE (ESD)

Precautions and Procedures

CAUTION

Electrostatic discharge can affect electronic components. Take precautions during furnace installation and service to protect the furnace’s electronic controls. Precautions will help to avoid control exposure to electrostatic discharge by putting the furnace, the control and the technician at the same electrostatic potential. Neutralize electrostatic charge by touching hand and all tools on an unpainted unit surface, such as thegas valve or blower deck, before performing any service procedure.

not proven within 2-1/2 minutes, the control goes into Watchguard-Pressure Switch mode for a 5-minute re-set period.

NOTE - The G24M furnace contains electronic components that are polarity sensitive. Make sure that the furnace is wired correctly and is properly grounded.

After the 15-second pre-purge period, the SureLight ignitor warms up for 20 seconds after which the gas valve opensfor a 4-secondtrial for ignition.The ignitor staysenergized for the first second of the 4-second trial. G24M units with 63K89, 24L85 or 56L83: the ignitor stays energizedthefirstsecondofthe4secondtrial.G24Munitswith board 97L48: ignitor stays energized during the 4-second trialuntilflameissensed.Ifignitionisnotproved during the 4-secondperiod,thecontrolwill try four more times withan inter purge and warm-up time between trials of 35 seconds.After a totalof five trialsfor ignition (including the initial trial), the control goes into Watchguard-Flame Failure mode.Aftera 60-minute reset period, the control willbegin the ignition sequence again. The SureLight control board has an added feature that prolongs the life of the ignitor. After a successful ignition, theSureLightcontrolutilizeslesspower to energize the ignitoron successive callsfor heat. Thecontrol continues to rampdown the voltageto the ignitor untilit finds the lowest amount of power that will provide a successful ignition. Thisamount of poweris used for255 cycles. Onthe 256th callfor heat, thecontrol will againramp down until the lowest power is determined and the cycle begins again.

c-Fan Time Control

The fan on time of 45 seconds is not adjustable. Fan off time (time that the blower operates after the heat demand has been satisfied) can be adjusted by flipping the dip switches located on the SureLight integrated control. The unit is shipped with a factory fan off setting of 90 seconds. Fan off time will affect comfort and is adjustable to satisfy individual applications. See figure 8.

NOTE—If fan “off” time is set too low, residual heat in heat exchanger may cause primary limit S10 to trip resulting in frequent cycling of blower. If this occurs, adjust blower to longer time setting.

b-Electronic Ignition

On a call for heat the SureLight control monitors the combustion air inducer prove switch. The control will not begin theheatingcycle if the prove switchisclosed (by-passed). Once the prove switch is determined to be open, the combustion air inducer is energized. When the differential in the prove switch is great enough, the prove switch closes and a 15-second pre-purge begins. If the prove switch is

FAN-OFF TIME ADJUSTMENT

60sec. 90sec. 120sec. 180sec.

To adjust fan-off timing, flip dip switch to desired setting.

FIGURE 8

Page 10

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 also monitors the flame, limit and gas valve operation. The control has a non--adjustable, factory preset on fan timing (45 seconds). Fan off timings are adjustable. The board utilizes both 120 and 24VAC. See figure 9. The board is also equipped with a 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 blowerisenergized.The LED flashes different codes to indicate problem conditions. The diagnostic LED lights red (not flashing) to indicate control board failure. T able 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 and pre-purge period has elapsed. It then opens the gas valve and generates a spark to ignite the burners. T rial for ignition lasts for 7 seconds. At the same time, the control begins monitoring the flame sensor.Iftheflame current is too weak (less than 1 microamp) or if the burners do not ignite (within the 7 second ignition trial), the control will shut off the spark ignitor and the com- bustion air blower and de-energize the gas valve. Flame current should be between 1and5microamps to keep the gas valve open. See figure 21.

The control will attempt to ignite the burners up to two more times. Each time the control restarts the ignition sequence, it begins with a 45 second pre-purge. If flame is not sensed after the third trial, the control locks out. Lockout means that the control shuts off the gas valve, spark and combustion air blower for 60 minutes. At the end of 60 minutes the control completely resets and will attempt ignition up to three times. The control can be manually reset before the end of 60 minutes by mo- mentarily turning off power to the unit.

DANGER

Shock hazard. Spark related components contain high voltage.

Disconnect power before servicing. Control is not field repairable. Ifcontrol is inoperable, simply re- place entire control.

Can cause injury or death. Unsafe operation will result if repair is attempted.

Page 11

SPARK OUTPUT

LINE VOLTAGE

TERMINAL

CONNECTIONS

EARLY MODEL G24M FURNACE CONTROL (A3)

24VAC VOLT

TERMINAL

CONNECTIONS

See Table 6 for

Terminal

Functions

DIAGNOSTIC

LED

TABLE 5

rnace Control A3 Limit Response During Operation

Response

Condition

Loss of Flame

Sensed Before

End of 45 se- cond Blower

On Delay

(3 or Fewer

Trials

for Ignition)

Loss of Flame

Sensed After

45 second Blower On Delay (3 or

Fewer Trials for Ignition)

Loss of Flame Sensed (More

Than 3 Trials

for Ignition)

Flame Sensed

Without

Demand

Primary or Secondary

Limit Open

Rollout Switch

Open

Combustion

Air Prove

Switch Open

Combustion

Air

Blower

Off Off Off 2 Flashes

On Off On 5 Flashes

On Off On 4 Flashes

On Off On 3 Flashes

Gas

Valve

(Spark

Starts

Within 0.8

seconds)

Off Then

On With

Spark

After Pre-

Purge

Supply

Blower

Diagnostic

Air

On Fast Flash

LED

FIGURE 9

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

Fan ON timing (timethattheburnersoperatebefore 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 cooling demand has 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

PLUG P20

FAN-OFF TIMING

SWITCHES

THERMOSTAT

CONNECTIONS

DANGER

Electrical Shock Hazard. This control contains field adjustable switches and also contains line voltage. Make sure power is disconnected before making any field adjust- ments or performing any service procedure.

NOTEIf fan off time is set too low,residualheat in heat ex

trip resulting in frequent cycling of blower. If this occurs, adjust blower to longer time setting.

changer may cause primary limit S10 to

Page 12

position. Figure 10 shows the various fa n 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 initiatedafteraheatingorcoolingdemandbutnotaftera 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 24V AC In From T ransformer

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

CMB RTN J20/P20 Pin 2

ACB HEAT 1/4 Spade

ACB LOW 1/4 Spade

ACB COOL 1/4 Spade

VLV HOT J20/P20 Pin 13 24VAC to Gas Valve VLV RTN J20/P20 Pin 9

PSW IN

HIL IN

HIL OUT

RO OUT J20/P20 Pin 7 24V AC Out T o Rollout Switches

RO IN J20/P20 Pin 15 24V AC In From Rollout Switches

SPARK

ELECTRODE

FS J20/P20 Pin 12 Flame Microamp Sensing

J20/P20

Pin 10

J20/P20

Pin 11

J20/P20

Pin 14

Male Spark

Plug Type

FAN-OFF TIME ADJU

LOCATED ON FURNACE CONTROL (A3)

Switched 120VAC to

Combustion Air Blower

120VAC Common

Combustion Air Blower

Switched 120VAC to

Blower Heating Tap

120VAC Output to Supply Air

Blower for Continuous Opera-

tion During No Demand

Switched 120VAC to Blower

Cooling Tap

24V AC Common From

Gas Valve

24VAC In From Pressure Switch

Switch Open: Prohibits Ignition

Switch Closed: Allows Ignition

24VAC In From Limits

Limit Open: Closes Gas Valve

Limits Closed: Allows Ignition

24VAC to Limit Train and Pressure Switch

High Voltage Out To

Spark Electrode

STMENT SWITCHES

Fan-Off Timings Switch 12

Off

On On

Off OnOff OffOn

Timing Seconds

90 120 180 240

FIGURE 10

Diagnostic LED

The furnace control is equipped with a diagnostic LED used for troubleshooting the unit and the control. LED functions are shown in table 7.

TABLE 7

Furnace Control A3 Diagnostic LED

LED State Meaning Remedy

Steady On Control Failure Replace Control

Slow Flash

Fast Flash

Two

Flashes

Three

Flashes

Four

Flashes

Five

Flashes

Normal Operation

and No Call For Heat

Normal Operation with Call For Heat

Control Lockout

Pressure Switch Open

Open Limit

Flame Sensed and Gas

Valve Not Energized.

----

Failed to Sense or Sustain

Flame. Check Gas Valve , Burners, Spark Electrode and Wire, Flame Sensor.

Replace Control If All OK. Failed to Prove Combus-

tion Blower Operation or

Blocked Vent. Repair or

Replace as Necessary.

Check Primary Limit, Rollout Switches and Sec- ondary Limits. Find source

of Overtemperature. If all

OK, Reset or Replace Lim-

its as Necessary.

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 capacitor motors to ensure maximum efficiency. See table8 for ratings.

TABLE 8

BLOWER MOTOR HP

G24M BLOWER RATI

G24MQ2 G24MQ3 G24MQ3/4 G24MQ4 G24MQ4/5 G24MQ5/6

SUPPLY AIR BLOWER

AND SECONDARY LIMITS

To Remove Blower From Unit: Remove Bolts and

Wiring Jackplugs. Then Slide Out Front of Unit.

FIGURE 11

NGS 120V 1PH

CAP 1/4 5MFD 370V 1/3 1/2 1/2 7.5MFD 370V 3/4 40MFD 370V 3/4 40MFD 370V

MOTOR

CAPACITOR

5MFD 370V

7.5MFD 370V

SECONDARY

LIMITS (S21)

Top

Left

Front

Bottom

BLOWER

MOTOR

Back

Right

Page 13

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 late model G24M units 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). For G24M units equippedwiththe SureLight ignition system, the blower will operate for 15seconds beforeburnerignition (pre purge) and for5 seconds after the the gas valve closes (post purge).

A pressure switch connected to the combustion air blower housing is used to prove combustion air blower operation. The switch monitors air pressure in the blow- er housing. During normal operation, the pressure in the housing is negative. If pressure becomes less negative (signifying an obstruction) the pressure switch opens. When the pressure switch opens, the furnace control (A3) immediately closes the gas valve to prevent burner operation.

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 switc h is located over the rightmost burner. The limit is a N.C. SPST manual-reset limit connected in series withtheignition control A3.WhenS47 senses 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 c an be c aus ed by a blocked flue or lack of combustion air. The switch is factory set and cannot be adjus ted. 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 loc ated on the control.

ROLLOUT SWITCH (S47)

MANUAL

RESET BUTTON

FIGURE 12

E--Primary Limit Control (S10)

LIMIT CONTROL FOR

G24M SERIES UNITS

THIS TYPE AUTO-RESET LIMIT

IS USED FOR THE PRIMARY LIMIT (S10) AND

RIGHT SECONDARY LIMIT (S21)

(see FIGURE 11)

FIGURE 13

The primary limit (S10) on G24M units is located in the middle of the heating vestibule panel. When excess heat is sensed in the heat exchanger, the limit will open. If the limit is tripped, the furnace control energizes the supply air blower and closes the gas valve. The limit automati- cally resets when unit temperature returns to normal. The switch is factory set and cannot be adjusted. The switch may have different setpoints for each unit model number . However, the setpoint will be printed on the side of the limit.

F--Secondary Limit Controls (S21)

The secondary limit (S21) on G24M units is located in the blower compartment in the back side of the blower housing. When excess heat is sensed in the blower compartment, the limit will open. If the limit is tripped, the furnace control energizes the supply air blower and closes the gas valve. The limit automatically resets when unit temperaturereturns to normal. The switch is factory set and cannot be adjusted. Two limits are supplied in each furnace and each limit is a different style (figures 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.

SECONDARY LIMIT CONTROL (S21)

FOR G24M SERIES UNITS

INSULATING COVER

SPADE CONNECTORS

LIMIT

THIS TYPE AUTO-RESET LIMIT IS

USED FOR THE LEFT SECONDARY

LIMIT (S21) (see FIGURE 11)

LIMIT

INSULATING C

OVER (s)

FIGURE 14

G--Spark Electrode and Flame Sensor

Early Model G24M Units

Figure 15 shows the arrangement of flame sensor, spark electrode and burners. The ignition control uses direct spark to ignite the rightmost burner and the burners cross-light to the left. The flame sensor uses flame rectification to sense combustion. A flame retention ring in the end of each burner is used to maintain correct flame length and shape and to keep the flame from lifting off the burner head. Figure 16 shows the gap between tip of the electrodes

and the burner surface.

Page 14

1/8(+1/64)

TYPICAL BURNER/ELECTRODE ORIENTATION

UPPER BURNER

MOUNTING RAIL

view looking at flame end of burners

BURNER

MANIFOLD ORIFICE

Top

Right Left

Bottom

GROUND

SPARK ELECTRODE

FLAME RETENTION RING

FIGURE 15

SPARK ELECTRODE TO BURNER GAP

11/16 in. 18 mm

1/32 in. 0.79

BURNER

1/4 in. 7 mm

1/32 in. 0.79

3/16 in.

4.7 mm

FLAME

SIDE VIEW END VIEW

SENSOR

FIGURE 16

H--Gas Valve

The G24M uses a gas

well (figure 17) or White Rodgers (figure 18). The valve is internally redundant to assure safety shut--off. If the gas valve must be replaced, the same type valve must be used.

24VAC terminals and gas control knob are located on top of the valve. All terminals on the gas valve are connected to wires from the electronic ignition control. 24V applied to the termin als energizes the valv e.

Inlet and outlet pressure taps are located on the valve. A regulator adjustmentscrew 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 regulato r conversion kit.

valve manufactured by Honey-

I--Combustion Air B lower 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.

LOWER BURNER

MOUNTING RAIL

FLAME SENSOR

(SOME UNITS MAY HAVE

SENSOR LOCATED IN MIDDLE OF BURNER)

TYPICAL ACCESS TO REGULATOR

FOR ADJUSTMENT AND L.P. CHANGEOVER

(Honeywell VR8205 series gas valve shown)

,1/(7

35(6685(

7$3

*$6 9$/9( 6+2:1 ,1 2)) 326,7,21

35(6685(

5(*8/$725

$'-867,1* 6&5(:

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635,1*

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35(6685(

*$6 ,1/(7

FIGURE 17

WHITE RODGERS

GAS VALVE

KNOB SHOWN

IN OFF POSITION

GAS INLET

35(6685(

7$3

36E GAS VALVE

REGULATOR

COVER SCREW

287/(7

35(6685(

7$3

,1/(7

7$3

35(6685(

7$3

Page 15

FIGURE 18

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.

PROVE SWITCH

COMBUSTION AIR BLOWER

PROVE SWITCH

Normally Open

Closes on Negative Pressure

Sensing Tube

Attaches to Top

Side Of Blower

III--START-UP A--Preliminary and Seasonal Checks

1 -- Inspect electrical wiring, both field and factory

installed for loose connections. Tighten as required.

2 -- Check voltage at disconnect switch. Voltage must

be within range listed on the nameplate. If not, consult the power company and have voltage condition corrected before starting unit.

B--Heating Start-Up

1 -- 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.

Top

PROVE

SWITCH

Back

Left

Right

Front

Bottom

FIGURE 19

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.Thetrip pres- sure is printed on the side of the limit.

The switch is factory set and is not field adjustable. It is asafetyshut-downcontrolinthe furnace and must not be bypassed for any reason.

II--PLACEMENT AND INSTALLATION

Make sure unit is installed in accordance with installa- tion instructions and applicable codes.

WARNING

Shock and burn hazard. G24M units are equipped with either a direct spark

or hot surface ignition system. Do not attempt to light 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 and main gas valves.

IMPORTANT

In case emergency shutdown is required, turn off the main shut-off valve and disconnect the main power to unit. These controls should be properly labeled by the installer.

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 16

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 supply piping should not allow more than 0.5W.C. drop in pressure between gas meter and unit. Supply gas pipe must not be smaller than unit gas connection.

Compounds used on gas piping threaded joints should be resistant to action of liquefied petroleum gases.

C--Testing Gas Piping

When pressure testinggaslines,thegas valve must be disconnected and isolated. Gas valves can be dam- aged if subjected to more than 0.5psig (14 W.C.). See figure 20.If the pressure is equal to or less than 0.5psig (14W.C.), use the manual shut--off valve before pres- sure testing to isolate furnace from gas supply.

underfire. High pressure can result in permanentdam- 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 connection must be be- tween 10.0 W.C. and 13.0 W.C.

On multiple unit installations, each unit should be checked separately,withandwithoutotherunits oper- ating. Supply pressure must fall within range listed in previous paragraph.

E--Check Manifold Pressure

After line pressure has been checked and adjusted, check manifold pressure. Move pressure gaugetoout- let pressure tap located on unit gas valve (GV1). Checks of manifold pressure are made 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.

GAS PIPING TEST PROCEDURE

MANUAL MAIN SHUT--OFF VALVE

WILL NOT HOLD TEST PRESSURE IN EXCESS OF 0.5 PSIG (14W.C.)

GAS VALVE

LINE PRESSURE TAP

CAP

FIELD PROVIDED

FIGURE 20

When checking piping connections for gas leaks, use preferred means. Kitchen detergents can cause harmful corrosion on various metals used in gas piping. Use of a specialty Gas Leak Detector is strongly recommended. It is available through Lennox under part number 31B2001. See Corp. 8411--L10, for further details.

Do not use matches, candles, flame or any other source of ignition to check for gas leaks.

D--Testing Gas Supply Pressure

When testing supply gas pressure, connect test gauge to inlet pressure tap (field provided). See figure 20. Check gas line pressure with unit firing at maximum rate. Low pressure may result in erratic operation or

IMPORTANT

For safety, connect a shut-off valve between the manometer and the gas tap to permit shut off of gas pressure to the manometer.

TABLE 9

GAS VALVE REGULATION

Unit (Fuel)

Natural L.P.

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

should burn mostly blue with some orange 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.

Operating Pressure (outlet) in. W.C.

3.5 +0 --0.3

9.5 +

0.5

Page 17

F- Proper Gas Flow

0 4500

4500 5500

5500 6500

6500 7500

Furnace should operate at least 5 minutes bef ore ch eckĆ ing gas flow. Determine time in seconds for two revoluĆ tions of gas through the meter. (Two revolutions assures a more accurate time.) Divide by two and compare to time in tabl e 10 below. Adjust manifold pressure on gas valve to match time needed.

NOTE- To obtain accurate reading, shut off all other gas appliances connected to meter.

TABLE 10

GAS METER CLOCKING CHART

Seconds for One Revolution

G24M

Unit

Natural LP

1 cu ft

Dial

2 cu ft

Dial

1 cu ft

Dial

2 cu ft

DIAL

-45 80 160 200 400

-60 60 120 150 300

-75 48 96 120 240

-100 36 72 90 180

-120 30 60 75 150

-140 26 52 64 128

Natural-1000 btu/cu ft LP-2500 btu/cu ft

NOTE- To obtain accurate reading, shut off all other gas appliances connected to meter.

G-High Altitude Derate

NOTE-In Canada, certification for installation at altiĆ tudes over 4500 ft. (1372m) above sea level is the jurisĆ diction of the local authorities.

G24M-1 through -9 Models

This unit does not require gas pressure adjustment, or pressure switch change when operating at elevations of 0 to 7500 ft. (0 to 2248m). Check gas line pressure with unit firing. The minimum pressure as shown on the nameplate for natural and propane gases must be maintained. No oriĆ fice change is required.

NOTE-This is the only permissible field derate for this appliance.

G24M-10 and -11 Models

Table 11 shows manifold pressure settings for installations at different altitudes. Refer to table 12 for pressure switch replacement for models at elevations of 4500 feet (1372m) and greater.

TABLE 11

ALTITUDE

feet (m)

0 - 4500

(0 - 1372)

4500 - 5500

(1372 - 1676)

5500 - 6500

(1676 - 1981)

6500 - 7500

(1372 - 2286)

GAS FUEL

Natural 3.5 (0.87)

Propane/LP 9.5 (2.36)

Natural 3.4 (0.86)

Propane/LP 9.2 (2.29)

Natural 3.3 (0.82)

Propane/LP 8.9 (2.21)

Natural 3.2 (0.80)

Propane/LP 8.6 (2.14)

MANIFOLD

PRESSURE

in. W.C. (kPa)

TABLE 12

Unit Model Pressure Switch Part Number

G24M-45 No Change

G24M-60 No Change

G24M-75 88J8001

G24M-100 18L2401

G24M-120 18L2401

G24M-140 No Change

IMPORTANT

For safety, shut unit off and remove manometer as soon as an accurate reading has been obtained. Take care to replace pressure tap plug.

H-Flame Signal

A microamp DC meter is needed to check the flame signal on the primary ignition control.

Flame (microamp) signal is an electrical current which passes from the furnace control through the sensor elecĆ trode during unit operation. Current passes from the senĆ sor through the flame to ground to complete a safety cirĆ cuit.

To Measure Flame Signal:

1 - Place meter in series between furnace control and

sensor wire. Connect the positive (+) lead of meter to

the ignition control sensor connection and the negaĆ

tive (-) lead of the meter to the sensor wire. See figure

21.

2 - Set thermostat for a heating demand and check flame

signal with unit operating. For G24M series with a RAM

control, a reading of 1 to 5 microamps DC should occur.

The furnace control must see at least 1.0 microamps in

order to keep the gas valve energized. G24M units with

the SureLight control should read 0.7 microamps or

more.

Page 18

FLAME SIGNAL TEST

D.C. MICROAMP

METER

FLAME

SENSOR

IGNITION

CONĆ TROL

SENSOR

WIRE

RAM CONTROL

SHOWN

SENSE"

TERMINAL

FIGURE 21

Flame signal from the Ram control may rise above 5 microĆ amps for the first few seconds after ignition then level off within the range.

WARNING

Fire and explosion hazard. These instructions MUST be followed exactly. Can cause a fire or explosion resulting in property damage, personal injury or loss of life.

V-TYPICAL OPERATING CHARACTERISTICS A-Blower Operation and Adjustment

NOTE- The following is a generalized procedure and does not apply to all thermostat controls.

1 - Blower operation is dependent on thermostat control

system.

2 - Generally, blower operation is set at thermostat subĆ

base fan switch. With fan switch in ON position, blower operates continuously on low speed. With fan switch in AUTO position, blower cycles with demand or runs conĆ tinuously while heating or cooling circuit cycles.

3 - In all cases, blower and entire unit will be off when the

system switch is in OFF position.

B-Temperature Rise

Temperature rise for G24M units depends on unit input, blower speed, blower horsepower and static pressure as marked on the unit rating plate. The blower speed must be

set for unit operation within the range of AIR TEMP. RISE

°F" listed in the unit rating plate.

To Measure Temperature Rise:

1 - Place plenum thermometers in the supply and return

air plenums. Locate supply air thermometer in the first

horizontal run of the plenum where it will not pick up raĆ

diant heat from the heat exchanger. 2 - Set thermostat to highest setting.

3 - After plenum thermometers have reached their highĆ

est and steadiest readings, subtract the two readings.

The difference should be in the range listed on the unit

rating plate. If the temperature is too low, decrease

blower speed. If temperature is too high, first check

the firing rate. Provided the firing rate is acceptable, inĆ

crease blower speed to reduce temperature. To

change blower speed taps see the Blower Speed Taps

section in this manual.

C-External Static Pressure

1 - Measure tap locations as shown in figure 22.

2 - Punch a 1/4" diameter hole

in supply and return air pleĆ

nums. Insert manometer

hose flush with inside edge

of hole or insulation. Seal

around the hose with perĆ

magum. Connect the zero

end of the manometer to the

discharge (supply) side of the system. On ducted sysĆ

tems, connect the other end of manometer to the reĆ

turn duct as above. For systems with non-ducted reĆ

turns, leave the other end of the manometer open to

the atmosphere. 3 - With only the blower motor running and the evaporator

coil dry, observe the manometer reading. Adjust blowĆ

er motor speed to deliver the air desired according to

the job requirements. 4 - External static pressure drop must not be more than

0.5" W.C.

5 - Seal around the hole when the check is complete.

STATIC PRESSURE

TEST

MANOMETER

G24M UNIT

FIGURE 22

Page 19

D-Blower Speed Taps Leadless Motors

Blower speed tap selection is accomplished by changing the taps at the blower motor harness connector. Disconnect harĆ ness connector from motor to expose speed selectors. Blower speed selections are listed in table 13.

To Change Blower Speed:

1 - Turn off electric power to furnace.

2 - Remove front panel and blower access door. See

figure 4.

3 - Disconnect blower motor harness from motor.

4 - Select desired speeds for heating and cooling (refer to

unit wiring diagram).

5 - Depress harness connector tab to release wire termiĆ

nal. Select connector location for new speed (refer to unit wiring diagram). Insert wire terminal until it is seĆ curely in place. See figure 23.

6 - Replace harness connector to motor.

BLOWER SPEED TAP SELECĆ

TION

LEADLESS MOTORS

HARNESS

CONNECTOR

SureLight board. The heating tap is connected to the "ACB HEAT " terminal and the cooling tap is connected to the "ACB COOL" terminal. The continuous blower tap is conĆ nected to the "ACB LOW" terminal. To change existing heat tap, turn off power then switch out speed tap on "ACB HEAT" with tap connected to "PARK M1" or "PARK M2". See table 14 for blower motor tap colĆ ors for each speed.

TABLE 13

TABLE 14

DEPRESS TAB TO RELEASE WIRE TERMINAL. SELECT CONNECTOR LOCATION FOR NEW SPEED (REFER TO UNIT WIRING DIAGRAM). INĆ SERT WIRE UNTIL IT IS SEĆ CURELY IN PLACE.

MOTOR

FIGURE 23

E-Blower Speed Taps Leaded Motors

Blower speed tap changes are made on the SureLight control board. See figure 6. Unused taps must be secured on dummy terminals "PARK M1" and or "PARK M2" on the

VI-MAINTENANCE

At the beginning of each heating season, the system should be checked as follows:

A-Filters

A filter must be used in order to ensure long life and proper operation. The filter is located in the return air duct or return air register. Filters must be cleaned or replaced when dirty to assure proper unit operation.

B-Heat Exchanger and Burners

NOTE-Use papers or protective covering in front of furĆ nace while cleaning furnace.

Due to dimples designed in the heatexchanger, cleaning is not recommended. Removal is for inspection only.

Page 20

To clean burners:

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 and ori-

fice in manifold. 8 -- Reinstall burner boxandgassupply 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.

CAUTION

Potential for gas leaks, fire or explosion. Some soaps used for leak detection are corrosive to certain metals. Carefully clean piping thor- oughly after leak detection has been completed. Can cause damage to piping resulting in gas leaks, fire or explosion.

C--Supply Air Blower

1 -- Check and clean blower wheel. 2 -- Motors used on the Lennox G24M series units

are permane ntly lubricate d 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.

HEAT EXCHANGER REMOVAL (unit shown in horizontal position)

REMOVE SCREWS (4)

Bottom

Front

Left

Back

Top

Right

SLIDE ENTIRE ASSEMBLY OUT OF CABINET

FIGURE 24

Page 21

VII--WIRING, OPERATION SEQUENCE &TROUBLESHOOTING A--Field Wiring, Thermostat Connections

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G24M and CONDENSING UNIT

THERMOSTAT DESIGNATIONS

(Refer to specific thermostat and outdoor unit.)

G24M

Condensing UnitThermostat

Furnace

HS UNIT

COOLING

COMPRESSOR

INDOOR BLOWER

HEAT

POWER

COMMON

HS UNIT

COMMON

),*85( 

3DJH 

B--Early Model G24M Series With Ram Ignition Control















1--W

hen disconnect is closed, 120V is routedthrough door interlock switch (S51) to feed the line voltage side of the furnace control (A3)andtransformerT1 primary. Door interlock switch must be closed for A3 and T1 to receive voltage.

2 -- T1 supplies 24VAC to terminal 24VAC on A3. In

turn, terminal R of A3 supplies 24VAC to termi- nal RC of the indoor thermostat (not shown).

3 -- When there is a call for heat, W1 of the thermostat

energizes W of the furnace control with 24VAC.

4 -- CMB BLWR of the blower control energizes the

combustion air blower (B6).Whenthe combustion air blower nears full speed, combustion air prove switch (S18) closes.

5 -- When S18 closes, assuming the flame rollout

switch (S47), primary limit (S10) and secondary



limits (S21) are closed, the furnace control begins a 45 second time-delay (pre-purge).

6 -- At the end of the pre-purge cycle, the furnace con-

trol simultaneously opens the gas valve andsends high voltage to the spark electrode.

7 -- When flame is sensed, the furnace control begins

a 45 second delay before energizing the indoor blower.

8 -- When heat demand is satisfied, W1 of the thermo-

stat de-energizes W of the furnace control and the furnace control immediately de-energizes the gas valve. 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 furnace control.

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?

YES

CONTROL SELF--CHECK OKAY?

YES

HI LIMIT SWITCH CLOSED?

YES

PRESSURE SWITCH OPEN?

YES

COMBUSTION AIR BLOWER ON?

PRESSURE SWITCH CLOSED?

YES

PREPURGE (45 seconds)

IGNITION TRIAL (7 seconds) ---- START IGNITION

SPARK, OPEN MAIN GAS VALVE. INCREMENT

TRIAL REGISTER. HAS FLAME BEEN REGISTERED

WITHIN 7 SECONDS?

YES

SYSTEM FAN ON.

(Fixed 45--second delay)

LOCKOUT: MAIN VALVE OFF

COMB. AIR AND SYSTEM FANS ON

RESET THERMOSTAT

LED: 5 flash if flame sensed with valve off

LED: Steady on if control board failure

CHECK TO SEE IF MAIN VALVE IS OFF.

SEQUENCE HOLDS UNTIL HI LIMIT CLOSES.

LED: 4 flashes.

CHECK TO SEE IF MAIN VALVE IS OFF.

SEQUENCE HOLDS UNTIL PRES. SWITCH OPENS.

LED: 3 flashes.

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 REGISTER

THREE TRIALS COMPLETED?

YES

IGNITION RESET PERIOD

COMBUSTION & SYSTEM FANS OFF.

IS 60 MIN. RESET PERIOD COMPLETE?

LED: Fast flash rate.

YES

FLAME SENSE OKAY?

YES

FLAME CONTINUOUSLY CHECKED?

ROLLOUT SWITCHES CLOSED

YES

HI LIMIT SWITCH CLOSED?

YES

PRESSURE SWITCH CLOSED?

YES

THERMOSTAT OPENS

LED: SLOW FLASH RATE

COMB. AIR BLOWER OFF (5 sec. delay)

FAN OFF (After selected 90, 120,

180, or 240 delay)?

MAIN VALVE AND SPARK OFF.

START IGNITION SPARK (IN 0.8 SEC. MAXIMUM).

HAS FLAME BEEN DETECTED WITHIN 7 SEC.?

YES

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

YES

COMBUSTION FAN ON. SYSTEM FAN OFF.

(AFTER DELAY TO OFF INTERVAL COMPLETED.)

LED: Fast flash rate.

3DJH 

RAM CONTROL

COOLING TROUBLE SHOOTING SEQUENCE

REMAINS UNCHANGED THROUGHOUT COOLING CYCLE.

THERMOSTAT CALLS FOR COOLING.

COMPRESSOR CONTACTOR AND SYSTEM FAN

ENERGIZED AT COOLING SPEED AFTER

1 SECOND DELAY. ACC TERMINAL ENERGIZED.

SYSTEM FAN AND ACC TERMINAL OFF AFTER

COMPLETING SELECTED DELAY INTERVAL

LED: Slow flash rate.

THERMOSTAT OPENS.

COMPRESSOR OFF.

(At dip switches).

MANUAL FAN TROUBLESHOOTING SEQUENCE

REMAINS UNCHANGED THROUGHOUT SEQUENCE.

MANUAL FAN SELECTION MADE AT THERMOSTAT.

CONTROL ENERGIZES SYSTEM FAN AT CONTINUOUS

THERMOSTAT CALLS FOR COOLING.

YES NO

SYSTEM FAN SWITCHED TO COOLING

SPEED. ACC TERMINAL REMAINS ENERGIZED.

THERMOSTAT OPENS.

SYSTEM FAN SWITCHES TO CONTINUOUS SPEED

AND ENERGIZES ACC TERMINAL. BOTH REMAIN ON

UNTIL MANUAL FAN IS SWITCHED OFF AT THERMOSTAT.

SLOW FLASH FAST FLASH 2 FLASH 3 FLASH 4 FLASH 5 FLASH STEADY ON

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.

LED: Slow flash rate.

SPEED. ACC TERMINAL ENERGIZED.

THERMOSTAT CALLS FOR HEAT.

LED CODES

YES

SYSTEM FAN SWITCHES TO HEATING SPEED AFTER

SELECTED DELAY. ACC TERM. REMAINS ENERGIZED.

THERMOSTAT OPENS.

SYSTEM FAN SWITCHED OFF AFTER DELAY.

ACC TERMINAL DE--ENERGIZED.

3DJH 

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.

Combustionairblower runs until S18 combustion air prove switch closes (switch must close within 2-1/2 minutes or control goes into 5 minute Watchguard Pressure Switch delay). Once S18 closes, a 15-second pre-purge follows.

4 - SureLight control energizes ignitor. A 20-second warm-up

period begins.

5 - Gas valve opens for a 4-second trial for ignition. Ignitor

staysenergizedthefirstsecond 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 indoor

blower B3. 8 - Whenheatdemandissatisfied,W1oftheindoorthermostat

de-energizes W of the SureLight control which de-ener-

gizes the gas valve. Combustion air blowerB6 continues a

5-second post-purge period, and indoor blower B3 com-

pletes a selected OFF time delay.

Page 26

SURELIGHT CONTROL HEATING

SEQUENCE OF OPERATION

NORMAL HEATING MODE ABNORMAL HEATING MODE

COMBUSTION AIR BLOWER ON FOR 1 SECOND.

SIGNAL IMPROPER

GROUND AT LED.

SIGNAL HOLDS

UNTIL UNIT IS

PROPERLY

GROUNDED.

IS COMBUSTION AIR BLOWER ENERGIZED?

(HTG ACC TERMINAL IS ENERGIZED WITH C.A.B.)

15-SECOND COMBUSTION AIR BLOWER PREPURGE

INITIATED BY CLOSED PRESSURE SWITCH.

POWER ON

CONTROL SELF--CHECK OKAY?

TURN INDUCER ON FOR 1 SECOND.

IS POLARITY REVERSED?

ROLLOUT SWITCH CLOSED?

(CONTINUOUS FLAME CHECK)

THERMOSTAT CALLS FOR HEAT:

PRESSURE SWITCH OPEN?

HAS COMBUSTION AIR PRESSURE SWITCH CLOSED IN 2.5 MINUTES?

IS THERE

PROPER GROUND?

YES

BURNER OFF?

YES

NORMAL OPERATION:

LED #1 ---- SLOW FLASH LED #2 ---- SLOW FLASH

LED #1 ---- FAST FLASH LED #2 ---- FAST FLASH

YES

IS COMBUSTION AIR

YES

CONTINUED NEXT PAGE

YES

IS VOLTAGE

ABOVE 75 VOLTS?

GAS VALVE OFF. COMBUSTION AIR BLOWER ON.

GAS VALVE OFF. COMBUSTION AIR BLOWER OFF.

(RESET CONTROL BY TURNING MAIN POWER OFF.)

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.

PRESSURE SWITCH IS IN WATCHGUARD MODE.

GAS VALVE OFF. COMBUSTION AIR BLOWER OFF.

INDOOR BLOWER OFF WITH DELAY.

LED #1 ---- OFF. LED #2 ---- SLOW FLASH.

IS 5-MINUTE RESET PERIOD COMPLETE?

INDOOR BLOWER ON.

LED #1 ALTERNATING FAST FLASH

LED#2 ALTERNATING FAST FLASH

CHECK FOR BROKEN IGNITOR OR

OPEN IGNITOR CIRCUIT

INDOOR BLOWER DELAY OFF.

LED #1 ON LED #2 ON

POLARITY REVERSED. LED #1 ---- FAST FLASH

LED #2 ---- SLOW FLASH

LOW VOLTAGE SIGNAL AT LED HOLDS

UNTIL VOLTAGE RISES ABOVE 75 VOLTS.

LED #1 ---- SLOW FLASH

LED #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 switch

closes or thermostat resets control.)

3DJH 

NORMAL HEATING MODE ABNORMAL HEATING MODE

15-SECOND COMBUSTION AIR INDUCER PREPURGE

INITIATEDBY CLOSED PRESSURE SWITCH.

YES

IGNITOR WARM-UP -- 20 SECONDS.

YES

4-SECOND TRIAL FOR IGNITION. GAS VALVE OPENS.

IGNITOR ENERGIZED FOR 1 SECOND AFTER VALVE OPENS. NO FLAME SENSED DURING THIS PERIOD.

BOARD 97L48: IGNITOR ENERGIZED DURING TRIAL OR

FLAME SIGNAL ABOVE 0.7 MICROAMPS?

UNTIL FLAME SENSED.

YES

FLAME STABILIZATION PERIOD.

4 SECONDS

FLAME RECTIFICATION CURRENT

CHECK. CAN FLAME BE PROVEN WITHIN

4 SECONDS AFTER GAS VALVE OPENS?

(>0.15 microamps)

YES

FLAME PRESENT?

YES

INDOOR BLOWER ON DELAYBEGINS

(45 seconds.)

YES

PRIMARY AND SECONDARY LIMIT

SWITCHES CLOSED?

YES

(See table 2 DIAGNOSTIC CODES for limit reset operation)

IS VOLTAGE ABOVE 75 VOLTS?

IS THERE A PROPER GROUND?

YES

IS IGNITOR INTACT AND CONNECTED?

GAS VALVE OFF. COMBUSTION AIR INDUCER ON.

HAS CONTROL FAILED TO SENSE FLAME FOR

FIVE CONSECUTIVE TRIES DURING A SINGLE

IGNITION WATCHGUARD MODE. GAS VALVE OFF.

LED 1 ALT. SLOW FLASH LED 2 ALT SLOW FLASH

IS 60-MINUTE RESET PERIOD COMPLETE?

GAS VALVE DE-ENERGIZED. COMBUSTION AIR INDUCER

DE-ENERGIZED.INDOOR BLOWER

ON UNTIL SWITCH CLOSES.LED #1

-- SLOW FLASH. LED #2 -- ON. IS LIMIT SWITCH CLOSED?

HAS PRIMARY/SECONDARY LIMIT RESET.

YES

INDOOR BLOWER OFF.

HEATDEMAND?

COMBUSTION AIR INDUCER OFF.

INDOOR BLOWER OFF WITH DELAY

HAS CONTROL RESET IGNITION

SEQUENCE FOUR TIMES?

LOW FLAME SIGNAL

(Does not affect operation of control)

LED #1 -- SLOW FLASH

LED #2 -- FAST FLASH

YES

LIMIT SWITCH WATCHGUARD MODE. GAS VALVE OFF. COMB. AIR INDUCER OFF. INDOOR BLOWER OFF WITH DELAY. LED#1-SLOW FLASH LED#2- ON. IS 60MINUTE RESET PERIOD COMPLETE.?

LEDS SIGNAL ALTERNATING

FAST FLASH

YES

ROLLOUT SWITCH CLOSED?

YES

COMBUSTION AIR PRESSURE

SWITCH CLOSED?

YES

THERMOSTAT DEMAND SATISFIED.

YES

LED #1 & #2 SIMULTANEOUS SLOW FLASHES.

YES

COMB. AIR INDUCER CONTINUES 5-SECOND POST PURGE

AFTER T’STAT DEMAND IS SATISFIED.INDOOR AIR BLOWER

COMPLETES SELECTED “OFF” DELAYBEFORE SHUTTING OFF.

ACB.HEATSPEED, HTG ACC TERM. AND ACC TERM. OFF.

HAS CAB SWITCH CLOSED IN 2.5 MINUTES?

COMBUSTION AIR INDUCER POWER OFF.

SEQUENCE HOLDS UNTIL ROLLOUT SWITCH IS RESET

GAS VALVE DE-ENERGIZED.

COMBUSTION AIR INDUCER ON.

INDOOR BLOWER OFF WITH DELAY

LED #1 -- OFF. LED #2 -- SLOW FLASH.

5-MINUTE PRESSURE SWITCH

GAS VALVE POWER OFF.

INDOOR BLOWER OFF WITH DELAY

LED #1 -- ON. LED #2 -- SLOW FLASH.

YES

WATCHGUARD MODE.

YES

Page 28

SURELIGHT CONTROL COOLING SEQUENCE

NORMAL COOLING MODE ABNORMAL COOLING MODE

POWER ON

IGNITION CONTROL MAIN POWER ON.

SIGNAL IMPROPER

GROUND AT LED.

SIGNAL HOLDS

UNTIL UNIT IS

PROPERLY

GROUNDED.

ROLLOUT SWITCH MONITORED CONTINUOUSLY.

CHECK FOR MAIN BURNER FLAME SENSE.

LED: SLOW FLASH RATE REMAINS UNCHANGED

CONTROL SELF DIAGNOSTIC CHECK.

IS CONTROL OPERATING NORMALLY?

YES

TURN INDUCER ON FOR 1 SECOND.

IS POLARITY REVERSED?

IS ROLLOUT SWITCH CLOSED?

IS MAIN BURNER FLAME OFF?

THROUGHOUT COOLING CYCLE.

THERMOSTAT CALLS FOR COOLING.

IS THERE

PROPER GROUND?

YES

IS VOLTAGE

ABOVE 75 VOLTS?

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.

SIGNAL POLARITY REVERSED AT LED.

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.

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.

LOW VOLTAGE SIGNAL AT LET HOLDS

UNTIL VOLTAGE RISES ABOVE 75 VOLTS.

COMPRESSOR CONTACTOR AND SYSTEM FAN

ENERGIZED WITH 0-SECOND DELAY

ACB COOL SPEED AND ACC. TERM. ENERGIZED.

THERMOSTAT OPENS.

COMPRESSOR OFF.

ACB COOL SPEED AND ACC. TERM. OFF

WITH 0-SECOND DELAY.

3DJH 

CONTINUOUS LOW SPEED FAN SEQUENCE OF OPERATION

LED: SLOW FLASH RATEREMAINS

UNCHANGED THROUGHOUT SEQUENCE.

MANUAL FAN SELECTION MADE ATTHERMOSTAT.

CONTROL (G) ENERGIZES SYSTEM FAN AT ACB

LOW SPEED. ACC. TERMINAL IS ENERGIZED.

THERMOSTAT CALLS FOR HEAT (W).

NO YES

THERMOSTAT CALLS FOR COOLING.

YES

SYSTEM FAN SWITCHED TO ACB COOL

SPEED. ACC. TERM. REMAINS ON.

THERMOSTAT OPENS.

HTG ACC. TERM. ENERGIZES

WITH COMB. AIR BLOWER.

BOARD NO. 63K8901

SYSTEM FAN DE-ENERGIZED. SYSTEM FAN

ENERGIZES ON ACB HEATSPEED AFTER

NORMAL DELAY.

BOARD NO. 24L85, 56L83, 97L48

SYSTEM FAN SWITCHES TO ACB HEAT SPEED

AFTER NORMAL DELAY (fan remains energized)

THERMOSTAT OPENS. COMBUSTION AIR AND HTG ACC TERMINAL DE-ENERGIZE.

BOARD 63K89: SYSTEM FAN OFF. ACC. TERM.

OFF. (AFTER OFF DELAY COMPLETED).

BOARDS 24L85, 56L83 AND 97L48:

SYSTEM FAN SWITCHES TO

LOW SPEED AFTER NORMAL DELAY.

(fan remains energized)

MANUAL FAN SELECTION MADE ATTHERMOSTAT.

CONTROL (G) ENERGIZES SYSTEM FAN AT ACB

LOW SPEED. ACC. TERM. ENERGIZED.

Page 30

E--SureLight Ignition Control Troubleshooting Guide

out code LED#2 Slow Flash

ACTION 1

Check wiring connections to

blowerdoesnot energize

blower does not energize

versed

120V field connection.

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 light

up.

LED#1--Off LED#2--Off

1.2

Diagnostic lights flash the roll--

out code.

LED#1--On, LED#2--Slow Flash

1.3

-- On initial power--up the comb. air .

-- Diagnostic lights flash the re-

verse polarity code.

Main voltage 120V not supplied to unit.

Miswiring of furnace or improper connections.

Circuit breaker tripped or fails to close.

Door interlock switch failure.

Transformer Failure.

Failed control board.

Roll--out switch open.

Roll--out switch failure.

Miswiring or improper connections at roll--out switch.

Nine pin connector failure

120V main power polarity re- versed.

1.1.1

1.1.2

1.1.3

1.1.4

1.1.5

1.1.6

1.2.1

1.2.2

1.2.3

1.2.4

1.3.1

ACTION 1 --

Determine cause of main power failure.

ACTION 1 --

to power make up box and transformer.

ACTION 2

board.

ACTION 1 --

set but does not have continuity.

ACTION 2 --

for short.

ACTION 1--

when door is closed.

ACTION 2 --

replace loose connectors.

ACTION 3 --

closed position. Replace if malfunctioning

ACTION 1 --

24V. Replace if malfunctioning

ACTION 1 --

checked, replace board.

ACTION 1 --

switch by pushing the top button.

ACTION 2 --

out switch activation before leaving furnace.

ACTION 1 --

switch. Replace roll--out switch if switch is reset but does not have continuity.

ACTION 1 --

switch.

ACTION 1 --

er connection to control board.

ACTION 2 --

plug pin.

ACTION 1 --

tral correctly input into control.

ACTION 2 --

120V field connection.

Check 120V main voltage.

Check for correct wiring of 120V

-- Check 24V wiring to control

Replace circuit breaker if it is re-

If circuit breaker still trips, check

Check thatdoor switch is activated

Check wire connections to switch,

Check continuity of switch in

Check that transformer output is

If all the above items have been

Manually reset the roll--out

Determine the cause of the roll--

Check continuity across roll--out

Check wiring connections to

Check 9--pin connector for prop-

Check continuity of the multi

Check the 120V has line and neu-

Reverse the line and neutral at the

LED#1--Fast Flash, LED#2--Slow Flash.

-- On initial power up the combus-

tion air blower does not energize.

-- Diagnostic lights flash normal

power on operation.

LED#1--Slow Flash LED#2--Slow Flash

1.4

1.4.1

Open combustion air blower motor circuit.

1.4.2

Failed combustion air blower mo- tor.

3DJH 

ACTION 1 --

blower. If no power, check wire and connec- tions.

ACTION 1 --

place blower.

Check for 120V to combustion air

If power is present at blower, re-

PROBLEM 1: UNIT FAILS TO OPERATE IN THE COOLING, HEATING, OR CONTINUOUS FAN MODE

fail

Condition Possible Cause Corrective Action / Comments

1.5

On initial power--up the combus-

tion air blower remains energized.

Diagnostic lights flash the im-

proper main ground.

LED#1--Alternating Fast Flash LED#2--Alternating Fast Flash

1.5.1

Improper ground to the unit.

1.5.2

6--Pin connector is improperly at-

tached to the circuit board.

1.5.3

Line voltage is below 75V.

ACTION 1 --

ground.

ACTION 2 --

the unit

ACTION 1--

installation. Correctly insert connector into control.

ACTION 1 --

above 75V. Determine cause of voltage drop and supply correct voltage to the control.

Check that the unit is properly

Install a proper main ground to

Check 6--pin connectorfor proper

Check that the line voltage is

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 im

proper main ground.

--Combustion airblower cycles 5

seconds on 55 seconds off.

LED#1--Alternating Fast Flash LED#2--Alternating Fast Flash

2.1.1

Open ignitor circuit.

2.1.2

Broken or failed ignitor.

ACTION 1 --

loose connectionsin theignitor circuit. Check mult--plug connections for correct installa- tion.

ACTION 1 --

tance across ignitor. If resistance does not read between 10.9and 19.7ohms, replacethe ignitor.

Check for correct wiring and

Unplug ignitor and read resis-

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 or

continuous fan demand.

Combustion air blower will not

start with a Heating demand.

-- Diagnostic lights flash the limit ure mode.

LED#1--Slow Flash, LED#2--On

3.2

-- Unit operates with a cooling and

continuous fan demand.

-- Combustion air blower will not

start with a Heating demand.

Diagnostic lights flash the pres-

sure switch failure code.

LED#1--Off, LED#2--Slow Flash

3.1.1

Primary or secondary (if equipped)

limit open.

3.1.2

Miswiring of furnace or improper

connections at limit switch(es).

3.2.1

Miswiring of furnace or improper

connections to combustion air

blower.

3.2.2

Pressure switch stuck closed.

ACTION 1 --

switch(es). Switches reset automatically upon cool down.

ACTION 2 --

inlet air (including filter) and outlet air. Deter- mine causefor limit activation before placing unit back in operation.

ACTION 1 --

loose connections. Correct wiring and/or re- place any loose connections.

ACTION 1 --

loose connections. Correct wiring and/or re- place any loose connections.

ACTION 1 --

open without the combustion air blower op- erating. Replace if malfunctioning

Check continuity across

Check for restrictions on blower

Check for correct wiring and

Check that the pressure switch is

3DJH 

PROBLEM 3: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER DOES

sure switch failure code 2.5 minutes

LED#2 Slow Flash

-- Unit operates with a cooling and

continuous fan demand.

Combustion air blower will not

start with a Heating demand.

Diagnostic lights flash the pres- sure switch failure code 2.5 minutes after heating demand.

LED#1--Off, LED#2--Slow Flash

PROBLEM 4: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER

Unit operates with a cooling and

continuous fan demand.

Combustion air blower ener-

gizes with a heating demand.

-- Diagnostic lights flash the pres- sure switch failure code 2.5 min- utes after heating demand.

LED#1--Off LED#2--Slow Flash

NOT ENERGIZE (CONT.).

Condition Possible Cause Corrective Action/Comments

3.3

3.3.1

Miswiring of furnace or improper

connections to combustion air

ACTION 1 --

loose connections. Correct wiring and/or re- place any loose connections.

Check for correct wiring and

blower.

3.3.2

Combustion air blower failure.

ACTION 1 --

blower and it does not operate, replace com- bustion air blower.

If there is 120V to combustion air

ENERGIZES, IGNITOR IS NOT ENERGIZED.

Condition Possible Cause Corrective Action/Comments

4.1

Pressure switch does not close

due to incorrect routing of the

pressure switch lines.

Pressure switch does not close

due to obstructions in the pressure

Pressure switch lines damaged

Pressure switch does not close

due to a low differential pressure

across the pressure switch.

Wrong pressure switch installed in

the unit, or pressure switch is out

Miswiring of furnace or improper

connections at pressure switch.

Pressure switch failure.

4.1.1

4.1.2

lines.

4.1.3

4.1.4

4.1.5

of calibration.

4.1.6

4.1.7

ACTION 1 --

lines are correctly routed. Correctly route pressure switch lines.

ACTION 1 --

the the pressure lines and/or taps.

ACTION 1 --

leaks. Replace any broken lines.

ACTION 1 --

across the pressure switch. This pressure should exceed the set point listed on the switch.

ACTION 2 --

exhaust vent. Remove all blockage.

ACTION 3 --

and run length. See installation instruc- tions.

ACTION 4 --

tion air blower.

ACTION 1 --

switch is installed in the unit. Replace pres- sure switch if necessary.

ACTION 1 --

loose connections. Correct wiring and/or re- place any loose connections.

ACTION 1 --

have been checked, the pressure switch may have failed. Replace pressure switch and de- termine if unit will operate.

Check that the pressure switch

Remove any obstructions from

Check pressure switch lines for

Check the differential pressure

Check for restricted inlet and

Check for proper vent sizing

Check voltage to thre combus-

Check that the proper pressure

Check for correct wiring and

If all the above modes of failure

3DJH 

PROBLEM 5: UNIT FAILS TO FIRE IN THE HEATING MODE, COMBUSTION AIR BLOWER

failed to ignite code.

ENERGIZES, IGNITOR IS ENERGIZED. (CONT.)

Condition Possible Cause Corrective Action/Comments

5.1

-- Unit operates with a cooling and continuous fan demand.

--Combustion airblower ener- gizes with Heating demand.

Ignitor is energized but unit fails

to light.

LED#1--Alternating Slow Flash LED#2--Alternating Slow Flash

5.1.1

Check that gas is being supplied to

the unit.

5.1.2

Miswiring of gas valve or loose

connections at multi--pin control

amp plugs or valve.

5.1.3

Malfunctioning gas valve or igni-

tion control.

ACTION 1 --

valve.Pressure should not exceed 13WC for both natural and propane. Line pressure should read a minimum 4.5 WC for natural and 8.0WC for propane.

ACTION 1 --

loose connections. Correct wiring and/or re- place any loose connections.

ACTION 1 --

gas valve approximately 35 seconds after heat demand is initiated.

ACTION 2 --

plied but valve does not open (check for ex- cessive gas line pressure before replacing gas valve).

ACTION 3 --

is not supplied to valve.

Check line pressure at the gas

Check for correct wiring and

Check that 24V is supplied to the

Replace the valve if 24V is sup-

Replace the control board if 24V

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 off prior to satisfying T--stat demand.

-- Diagnostic lights flash the pres- sure switch code.

6.1.1

Low pressure differential at the

pressure switch.

ACTION 1 --

exhaust. Remove all blockage.

ACTION 2:

installation instructions.

Check for restricted vent inlet or

Check for proper vent sizing. See

LED#1--Off LED#2--Slow Flash

-- Combustion air blower energizes with a heating demand.

-- Burners light but fail to stay lit.

-- After 5 tries the control diagnos- tics flash the watchguard burners failed to ignite code.

LED#1--Alternating Slow Flash LED#2--Alternating Slow Flash

6.2

6.2.1

Sensor or sense wire is improperly

installed.

6.2.2

Sensor or sense wire is broken.

6.2.3

Sensor or sensor wire is grounded

to the unit.

6.2.4

Control does not sense flame.

ACTION 1 --

located (page 10) and that the sense wire is properly attached to both the sensor and the control.

ACTION 1 -- ACTION 2 --

wire. If wire or sensor are damaged replace the component.

ACTION 1 --

the sensor rod and the unit ground.

ACTION 2 --

the sensor wire and the unit ground.

ACTION 3 --

cuit.

ACTION 1 --

from the burner flame. If the microamp sig- nal is below 0.70 microamps, check the sense rod for proper location or contamina- tion.

ACTION 2 --

flame sense rod. If rod is to be cleaned, use steel wool or replace sensor. DO NOT CLEAN ROD WITH SAND PAPER. SAND PA- PER WILL CONTRIBUTE TO THE CONTAMI- NATION PROBLEM. to bend sense rod.

Check that sensor is properly

Check for a broken sensor. Test continuity across the sense

Check for resistance between

Correct any shorts found in cir-

Check the microamp signal

Replace, clean, or relocate

Do not attempt

NOTE:

3DJH 

PROBLEM 6: BURNERS LIGHT WITH HEATING DEMAND BUT UNIT SHUTS DOWN

guard flame failure

Condition Possible Cause Corrective Action/Comments

6.3

-- Combustion air blower ener- gizes with a heating demand.

-- Burners light.

-- Roll--out switch trips during the heating demand.

-- Diagnostic lights flash roll--out failure.

LED#1--On LED#2--Slow Flash

6.4

Combustion air blower ener-

gizes with a heating demand.

-- Burners light roughly and the unit fails to stay lit.

-- Diagnostic lights flash watch-

uard flame failure.

PREMATURELY (CONT.)

6.3.1

Unit is firing above 100% of the

nameplate input.

6.3.2

Gas orifices leak at the manifold

connection.

6.3.3

Insufficient flow through the heat

exchanger caused by a sooted or

restricted heat exchanger.

6.3.4

Burners are not properly located in

the burner box.

6.4.1

Recirculation of flue gases. This

condition causes rough ignitions

and operation. Problem is charac-

terized by nuisance flame failures.

ACTION 1 --

matches value listed on nameplate. See installation instructions for proper proce- dure.

ACTION 2 --

size match the size listed on the nameplate or installation instructions.

ACTION 3 --

insure no leaks are present.

ACTION 4 --

matches value listed on nameplate.

ACTION 1 -- NOTE: ACTION 2 --

threaded orifice connection. Use approved method for leak detection (see unit instruc- tions).

ACTION 1 --

er restrictions in the heat exchanger assem- bly.Clean assembly as outlined in instruction manual.

ACTION 2--

proper combustion and flow. CO2 should measure between 6.0% and 8.0% for NG and between 6.5% and 8.5% for LP. CO should measure below .04% (400PPM) in an air--free sample of flue gases for either NG or LP.

ACTION 1 --

into the center of the heat exchanger open- ings. Correct the location of the burners if necessary.

ACTION 1 --

gases away from intake vent. Remove any obstacles in front of the intake and exhaust vent which would cause recirculation.

ACTION 2 --

haust vent installation. See instructions

Check that the manifold pressure

Verify that the installed orifice

Check gas valve sensing hose to

Check the input rate to verify rate

Tightenorifice untilleak issealed.

Be careful not to strip orifice threads.

Check for gas leakage at the

Checkfor sooting deposits or oth-

For G24Mgas furnaces, check for

Check that the burners are firing

Check for proper flow of exhaust

Check for correct intake and ex-

LED#1--Alternating Slow Flash LED#2--Alternating Slow Flash

6.4.2

Improper burner cross--overs

3DJH 



ACTION 1 --

cross--overs for burrs, or any restriction or if crossover is warped. Remove restriction or replace burners.

Remove burner and inspect the

PROBLEM 6: BURNERS LIGHT WITH HEATING DEMAND BUT UNIT SHUTS DOWN

sense code

6.5

-- Combustion air blower ener- gizes with a heating demand.

-- Burners light.

-- Diagnostic lights flash watch guard flame failure.

-- NOTE Unit might go into 60 minute Watchguard mode depend- ing on intermittent nature of sen- sor signal.

LED#1--Alternating Slow Flash LED#2--Alternating Slow Flash

PROBLEM 7: CONTROL SIGNALS LOW FLAME SENSE DURING HEATING MODE

Condition Possible Cause Corrective Action/Comments

7.0

-- Unit operates correctly but the diagnostic lights flash low flame

LED#1--Slow Flash LED#2--Fast Flash

PREMATURELY (CONT.)

6.5.1

Loose sensor wire connection

causes intermittent loss of flame

signal.

7.1.1

Sense rod is improperly located on

the burner.

7.1.2

Sense rod is contaminated.

ACTION 1 --

located.

ACTION 2 --

erly attached to both the sensor and the con- trol. Pay extra attentionto thepin connectors.

ACTION 1 --

location on the burner. Properly locate the sense rod or replace if rod cannot be located correctly.

ACTION 1 --

tion or coated surface. Clean the sense rod with steel wool or replace sensor. DO NOT USE SAND PAPER TO CLEAN ROD. SAND PAPER WILL CONTRIBUTE TO THE CON- TAMINATION PROBLEM.

Check that the sensor is properly

Check that the sense wire isprop-

Check the sense rod for proper

Check sense rod for contamina-

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 in continuous fan, cooling, or heating mode.

Miswiring of furnace or improper

connections at control or indoor

120V is not being supplied to the

indoor air blower or blower motor

Defective control board

8.1.1

blower motor.

8.1.2

failure.

8.1.3

ACTION 1--

loose connections. Check for correct wiring and loose connections.

ACTION 1 --

calls for indoor blower by energizing Y, G, and W individually on thelow voltage terminal strip. Note that when W is ener- gized, the blower is delayed 45 seconds. If there is 120V to each motor tap but the blow- er does not operate, replace the motor.

ACTION 1 --

G, orW is energized, replace the control.

Correct wiring and/or replaceany

Check for 120V at the various

If there is not 120V when Y,

PROBLEM 9: RF STATIC DURING TIME FOR IGNITION

Condition Possible Cause Corrective Action/Comments

9.0

-- AM radio interference.

9.1.2

Ignitor operation

ACTION 1 --

Call Technical Support, Dallas.

3DJH 

Lennox G24M User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

SPECIFICATIONS

BLOWER DATA