Lennox G24M SERIES Installation and operation manual

Page 1 ã1998 LennoxIndustriesInc.
Litho U.S.A.
Corp.9723-L12 G24M
Service LiteratureRevised 07-2001
G24MSERIES UNITS
G24Mseriesunitsaremid-efficiencygasfurnacesmanufac-
tured withtubularsteelheatexchangersformed ofalumi-
nizedsteel.G24Munitsareavailableinheatingcapacitiesof
45,000 to 140,000 Btuh and cooling applicationsup to 5
tons.RefertoEngineering Handbookforpropersizing.
Unitsarefactoryequipped forusewith naturalgas.Akitis
availableforconversiontoLPGoperation.EarlymodelG24M
unitsuse electronic(directspark)ignition.LatemodelG24M
modelunitsfeaturethe LennoxSureLightTsilicon-nitride
ignition system.The G24MXunitmeetsthe CaliforniaNitro-
gen Oxides(NOx)Standardsand CaliforniaSeasonalEffi-
ciency requirements.All unitsusearedundantgas valveto
assuresafety shut-off asrequired byA.G.A.orC.G.A.
Unitsmaybeinstalledinupflow,downfloworhorizontalposi-
tion.The heatexchangerisdesigned foruprightorhorizon-
taluse only.When the unitisinstalled inthe downflowposi-
tion,theheatexchangerisfieldremovedandreinstalledsoit
isuprightwhenthecabinetisinverted.Nofieldconversion is
required when the unitisinstalled inthe horizontalposition.
The heatexchanger,burnersand manifold assembly can
easilybe removed forinspection and service by simplydis-
connecting gas,unplugging wiring harness and sparkwires
and removing fourscrewsholding the heatexchangerin
place.Then the heatexchangerslidesoutof the cabinet.
All specificationsinthismanualaresubject tochange.Pro-
ceduresoutlined inthismanualare presented asarecom-
mendation onlyand do notsupersede or replacelocalor
statecodes. Inthe absence oflocalorstatecodes, the
guidelinesand proceduresoutlined inthismanual(except
where noted)arerecommended onlyand do notconstitute
code.
SPECIFICATIONS
ModelNo.G24M2(X)-45 G24M2-60 G24M3(X)-60 G24M2-75 G24M3(X)-75
InputBtuh (kW)45,000 (13.2)60,000 (17.6)75,000 (22.0)
OutputBtuh (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%
CaliforniaSeasonalEfficiency 75.4%76.4%75.9%76.8%76.8%
Flue sizeconnection diameter—in.(mm) round 3 (76)4(102)
Temperatureriserange —_F(_C)30 -60 (17 -33)45 -75 (25 -42)
High static certified byA.G.A./C.G.A.—inwg.(Pa).50 (125)
GasPiping SizeI.P.S.NaturalorLPG/propane 1/2(13)
B
l
o
w
e
r
w
h
e
e
l
n
o
m
i
n
a
l
in.9x7 10 x7 9 x7 10 x7
B
l
o
w
e
r
w
h
e
e
l
n
o
m
i
n
a
l
d
i
a
m
e
t
e
r
x
w
i
d
t
h
mm 229 x178 254 x178 229 x178 254 x178
Blowermotoroutput—hp (W)1/4(187)1/3(224)1/4(187)1/3(224)
N
o
m
i
n
a
l
c
o
o
l
i
n
g
Tons1,1-1/2 or2 2,2-1/2 or3 1,1-1/2 or2 2,2-1/2 or3
N
o
m
i
n
a
l
c
o
o
l
i
n
g
t
h
a
t
c
a
n
b
e
a
d
d
e
d
kW3.5,5.3 or7.0 7.0,8.8 or10.6 3.5,5.3 or7.0 7.0,8.8 or10.6
Shipping weight—lbs.(kg)1 package 130 (59)135 (61)
Electricalcharacteristics 120 volts—60 hertz—1 phase(less than 12 amps)All models
bOptionalAccessories (MustBeOrderedExtra)b
LPG/propane kitLB-69845L (38K84)
Twinning Kit96J69 —5lbs.(2kg)
Up-Flow/HorizontalFilterand FilterRack Kits
}No.&size of filters-in.(mm)Single(32J02)Ten Pack (66K64) (1)16 x20 x1(406 x508 x25)
¡
D
o
w
n
-
f
l
o
w
Catalog No.LB-69843A(32J01)—3lbs.(1kg)
¡
D
o
w
n
-
f
l
o
w
FilterKitNo.& Size ofFilters—in.(mm)(2)16 x20 x1(406 x508 x25)
Down-flow CombustibleFloorBaseLB-79239A(67J91)—10 lbs.(4kg)
Sidewall PowerVenting Kit79J15 —25 lbs.(11 kg)
Hanging BracketKitLB-69957 (46J66)—15 lbs.(8kg)
lAnnualFuel Utilization Efficiency based on U.S.DOEtestproceduresand according toFTC labeling regulations. Isolated combustion system rating fornon-weatherized
furnaces.
}Polyurethane frametype filterisfurnished withkit.
¡Filtersare not furnished withkitand mustbe 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)
R 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  E F( E C) 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 nominal
in. 12 x 8 12 x 9
Bl
ower w
h
ee
l
nom
i
na
l
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 6
N
om
i
na
l
coo
li
ng
that 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 Kits
c No. & size of filters -- in. (mm) Single (
32J02
) Ten Pack (
66K64
)
(1) 16 x 20 x 1 (406 x 508 x 25) Single
(46J14)
Ten Pack
(66K65)
(1) 20 x 20 x 1 (508 x 508 x 25)
Catalog No. LB-69843A
(32J01)
 3 lbs. (1 kg)
o Down-flow
Filter 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)
10lbs.(4kg) 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)
R
Annual Fuel Utilization Efficiency based on U.S. DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating f or non-weatherized
furnaces.
c
Polyurethane frame type filter is furnished with kit.
o
Filters 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)
R A.F.U.E. 80.0% 80.1% 80.0%
California Seasonal Efficiency Not Available 75.5% Not Available
o Flue size connection diameter  in. (mm) round 4 (102) 5 (127)
Temperature rise range  E F( E C) 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 nominal in. 12 x 8 12x9
Blower wheel nominal
diameter x width mm 305 x 203 305 x 229
Blower motor output  hp (W) 1/2 (373) 3/4 (560)
Nominal coolin
g
Tons 2, 2-1/2, 3, 3-1/2 or 4 3-1/2, 4, 5 or 6
Nominal cooling
that 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 Kits
c No. and size of filters -- in. (mm) Single
(46J14)
Ten Pack
(66K65)
(1) 20 x 20 x 1 (508 x 508 x 25) Single
(58J93)
Ten Pack
(66K66)
(1) 20 x 20 x 1 (508 x 508 x 25)
Catalog No. LB-69843A
(32J01)
 3 lbs. (1 kg)
w Down-flow
Filter Rack
No. & Size in. (2)16x20x1
Filter 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)
R
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.
c
Polyurethane frame type filter is furnished with kit.
o
2 in. x 5 in. (51 mm x127 mm) flue adaptor furnished with -140 input furnaces for connection to furnace induced draft blower.
w
Filters are not furnished with kit and must be ordered extra.
BLOWER DATA
G24M2-45, G24M2-60 AND G24M2-75 BLOW ER PERFORMANCE
External Static Air Volume at Various Blower Speeds
External Static
Pressure High Medium-High Medium-Low Low
in. w.g. Pa cfm L/s cfm L/s cfm L/s cfm L/s
0 0 1270 600 980 460 770 365 570 270
.05 12 1245 590 975 460 770 365 565 265
.10 25 1220 575 975 460 770 365 565 265
.15 37 1195 565 965 455 765 360 560 265
.20 50 1170 550 960 455 760 360 560 265
.25 62 1140 540 950 450 760 360 555 260
.30 75 1110 525 940 445 760 360 550 260
.40 100 1060 500 910 430 750 355 545 255
.50 125 990 465 880 415 740 350 540 255
.60 150 900 425 810 380 690 325 530 250
.70 175 800 380 740 350 630 295 520 245
NOTE  All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished) in place. Also see Filter Air Resistance table

3DJH 
BLOWER DATA
G24M3-60 AND G24M3-75 BLOWER PERFORMANCE
External Static
Air Volume at Various Blower Speeds
External Static
Pressure High Medium-High Medium-Low Low
in. w.g. Pa cfm L/s cfm L/s cfm L/s cfm L/s
0 0 1425 670 1240 585 1000 470 800 380
.05 12 1415 670 1230 580 995 470 800 380
.10 25 1400 660 1220 575 990 465 795 375
.15 37 1385 655 1200 565 985 465 795 375
.20 50 1370 645 1180 555 980 460 790 375
.25 62 1350 635 1160 545 970 460 780 370
.30 75 1330 630 1140 540 955 450 770 365
.40 100 1280 605 1095 515 925 435 750 355
.50 125 1210 570 1040 490 900 425 720 340
.60 150 1135 535 985 465 860 405 680 320
.70 175 1070 505 920 435 800 380 630 300
NOTE  All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished) in place. Also see Filter Air Resistance table
G24M4-75, G24M3/4-100 AND G24M3/4-120 BLOWER PERFORMANCE
External Static Air Volume at Various Blower Speeds
External Static
Pressure High Medium-High Medium Medium-Low Low
in. w.g. Pa cfm L/s cfm L/s cfm L/s cfm L/s cfm L/s
0 0 1830 865 1600 755 1325 625 1070 505 880 415
.05 12 1815 855 1585 750 1320 625 1070 505 880 415
.10 25 1800 850 1570 740 1315 620 1070 505 880 415
.15 37 1875 885 1550 730 1310 620 1065 505 875 415
.20 50 1750 825 1530 720 1300 615 1060 500 875 415
.25 62 1725 815 1515 715 1290 610 1050 495 870 410
.30 75 1700 800 1500 710 1275 600 1040 490 870 410
.40 100 1650 780 1460 690 1245 590 1020 480 860 405
.50 125 1600 755 1420 670 1210 570 1000 470 840 395
.60 150 1550 730 1380 650 1170 550 980 460 820 385
.70 175 1480 700 1330 630 1130 535 960 455 790 375
NOTE  All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished) in place. Also see Filter Air Resistance table

3DJH 
BLOWER DATA
G24M4/5-100, G24M4/5-120 AND G24M4/5-140 BLOWER PERFORMANCE
External Static Air Volume at Various Blower Speeds
External Static
Pressure High Medium-High Medium Medium-Low Low
in. w.g. Pa cfm L/s cfm L/s cfm L/s cfm L/s cfm L/s
0 0 2450 1155 2160 1020 1970 930 1700 800 1500 710
.05 12 2440 1150 2155 1015 1965 925 1695 800 1500 710
.10 25 2430 1145 2150 1015 1960 925 1690 800 1495 705
.15 37 2415 1140 2135 1010 1950 920 1685 795 1495 705
.20 50 2400 1135 2120 1000 1940 915 1680 795 1490 705
.25 62 2380 1125 2105 995 1930 910 1675 790 1480 700
.30 75 2360 1115 2090 985 1915 905 1670 790 1470 695
.40 100 2310 1090 2050 965 1870 880 1650 780 1440 680
.50 125 2260 1065 2000 945 1810 855 1610 760 1410 665
.60 150 2180 1030 1950 920 1750 825 1560 735 1370 645
.70 175 2100 990 1890 890 1700 800 1520 715 1330 630
NOTE  All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished) in place. Also see Filter Air Resistance table
FILTER AIR RESISTANCE
cfm (L/s) in. w.g. (Pa)
0 (0) 0.00 (0)
200 (95) 0.01 (2)
400 (185) 0.03 (7)
600 (280) 0.04 (10)
800 (375) 0.06 (15)
1000 (470) 0.09 (22)
1200 (560) 0.12 (30)
1400 (655) 0.15 (37)
1600 (750) 0.19 (47)
1800 (845) 0.23 (57)
2000 (935) 0.27 (67)
2200 (1030) 0.33 (82)
2400 (1125) 0.38 (95)
2600 (1220) 0.44 (110)

Page 6
FIGURE 1
G24M
PARTS IDENTIFICATION
VENT ADAPTER CABINET TOP
G24M
CABINET
CABINET
BOTTOM
HEAT EXCHANGER
ASSEMBLY
BURNER
ASSEMBLY
BLOWER ASSEMBLY
COMBUSTION AIR
BLOWER
FLUE BOX
SECONDARY
LIMITS
FRONT LOUVERED
PANEL
DOOR INTERLOCK SWITCH
CONTROL
BOARD
TRANSFORMER
PRESSURE
SWITCH
NOx
TURBULATOR
LOW PRESSURE SWITCH
(Propane Only)
PRIMARY
LIMIT
FIGURE 2
HEATING COMPONENTS (shown in horizonta l position)
HEAT EXCHANGER
COMBUSTION AIR BLOWER
MANIFOLD
ROLLOUT SWITCH (2)
COMBUSTION AIR
PROVE 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)
FLAME
SENSOR
MANIFOLD
ORIFICE GAS VALVE
HEAT EXCHANGER
VEST PANEL
BURNER
UPPER
BURNER
MOUNTING
RAIL
LOWER
BURNER
MOUNTING
RAIL
BURNER BOX
BURNER BOX
TOP
Front Right
Bottom
Left Back
PRIMARY LIMIT
ROLLOUT
SWITCHES
SURELIGHT
IGNITOR
FIGURE 4
To Access Blower:
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.
G24M BLOWER DOOR COMPONENTS -- BLOWER ACCESS
Top
Bottom
Left
Right
Back
Front
4
1
J1/P1
J135/
P135
2
3
5
6

Page 8
I-UNIT COMPONENTS (Figures 1, 2, 3)
24M 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.
24M 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 Com onents (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 ower before servicing. Control is not
field re airable. If control is ino erable, sim ly
re lace entire control.
Can cause injury or death. Unsafe o eration will
result if re air is attem ted.
3- SureLight Ignition System (A3)
Late Model G24M Units
Late model 24M units are equipped with the Lennox
SureLight ignition system. The system consists of ignitor
(figure 5) and ignition control board (figure 6 with control
terminal designations in table 1). The board and ignitor
work in combination to ensure furnace ignition and ignitor
durability. The SureLight integrated board controls all
major furnace operations. The board also features two
LED lights for troubleshooting and two accessory termiĆ
nals rated at (4) four amps. See table 2 for troubleshootĆ
ing diagnostic codes. Table 3 and 4 show jack plug termiĆ
nal designations. Units equipped with the SureLight
board can be used with either electronic or electro-meĆ
chanical thermostats without modification. The SurĆ
eLight ignitor is made of durable silicon-nitride. Ignitor
longevity is also enhanced by voltage ramping by the
control board. The board finds the lowest ignitor temperaĆ
ture which will successfully light the burner, thus increasĆ
ing the life of the ignitor.
a-flame sensor
The flame sensor uses flame rectification to sense comĆ
bustion. During operation, flame is sensed by current
passed through the flame and sensing electrode. Figure 7
shows the gap between tip of the electrode and the burner
surface.
FIGURE 5
SURELIGHT IGNITOR BURNER ASSEMBLY
FLAME SENSOR
FLAME RETENTION RIN
UPPER BURNER
MOUNTIN RAIL ORIFICE
SURELIGHT IGNITOR

Page 9
SURELIGHTCONTROLBOARD
LATEMODELG24MUNITS
FIGURE6
SURELIGHTCONTROL TERMINALDESIGNATIONS
ACBCOOL
ACBHEAT
PARK
ACBLOW
ACC
TX
HOT
HTGACC
NEUTRALS
24VAC HOT
24VAC RTN
FLAME SENSE
Blower - Cooling Speed (Line Volt)
Blower - Heating Speed (Line Volt)
AlternateBlowerSpeeds(Dead)
ContinuousLowSpeed Blower
AccessoryTerminal(Line Volt)
120VAC Hot toTransformer
120VAC Hot Input
HeatOnlyAccessory(Line Volt)
120VAC Neutrals
24VAC Hot fromTransformer
24VAC ReturnfromTransformer
FlameSenseTerminal
TABLE1
FIGURE7
NORMAL FLAME SIGNAL>0.7MICROAMPS
LOWFLAME SIGNAL<0.7MICROAMPS
MINIMUMFLAME SIGNAL<0.15 MICROAMPS
FLAME SENSORTOBURNERGAP
BURNER
FLAME
SENSOR
SIDE VIEWEND VIEW
1/4in.7mm
¦1/32 in.0.79
mm 3/16 in.
4.7mm
11/16 in.18 mm
¦1/32 in.0.79
mm
TABLE2
DIAGNOSTIC CODES
MAKE SURETO IDLED’SCORRECTLY:REFERTO INSTALLATIONINSTRUCTIONSFOR CONTROLBOARD LAYOUT.
LED#1 LED#2 DESCRIPTION
SIMULTANEOUS
SLOWFLASHSIMULTANEOUS SLOWFLASHPower - Normaloperation
Alsosignaled during cooling and continuesfan.
SIMULTANEOUSFAST
FLASHSIMULTANEOUSFAST FLASHNormaloperation -signaled when heating demand initiated at thermostat.
SLOWFLASHON
PrimaryorSecondarylimitopen.Unitswith board 63K8901 or24L85:Limitmust
closewithin5trialsforignition orboard goesinto one hourlimitWatchguard.
Unitswith board 56L83 or97L48:Limitmustclosewithin3minutesorboard
goesinto one hourlimitWatchguard.
OFF SLOWFLASHPressureswitch open orhasopened 5 timesduringasinglecall forheat; OR:
Blocked inlet/exhaustvent; OR:Condensateline blocked;OR:Pressureswitch
closed priorto activation ofcombustion airblower.
ALTERNATINGSLOW
FLASHALTERNATINGSLOW FLASHWatchguard-burnersfail toignite.
SLOWFLASHOFF Flamesensed withoutgas valve energized.
ONSLOWFLASHRolloutswitch open.OR:9 pinconnectorimproperlyattached.
ON
ON
OFF
ON
OFF
ONCircuitboardfailure orcontrolwired incorrectly.
FAST FLASHSLOWFLASHMain powerpolarityreversed.Switchline and neutral.
SLOWFLASHFAST FLASHLowflamesignal.Measuresbelow.7microAmps.Replaceflamesenserod.
ALTERNATINGFAST
FLASHALTERNATINGFAST FLASHImpropermain ground orline voltage below75 volts;OR:Broken ignitor;OR:
Open ignitorcircuit.
NOTE-Slowflash equals1Hz(one flash persecond).Fast flash equals3Hz(three flashespersecond).Drop out flamesensecurrent<0.15 microAmps

Page 10
TABLE3
SureLightBOARD J156 (J2)TERMINAL
DESIGNATIONS
PIN#FUNCTION
1Ignitor
2NotUsed
3IgnitorNeutral
4Combustion AirBlowerLine Voltage
5NotUsed
6Combustion AirBlowerNeutral
TABLE4
SureLightBOARD J58 (J1)TERMINAL
DESIGNATIONS
PIN#FUNCTION
1PrimaryLimit In
2GasValveCommon
3Roll OutSwitchOut
4GasValve 24V
5PressureSwitchIn
6PressureSwitch and PrimaryLimitOut
7NotUsed
8Roll OutSwitchIn
9Ground
CAUTION
Electrostaticdischarge canaffectelectronic
components.Take precautionsduring furnace
installation and service to protect thefurnace’s
electronic controls.Precautionswill helpto
avoidcontrolexposuretoelectrostaticdis-
chargebyputting thefurnace,the controland
thetechnicianat the same electrostaticpoten-
tial. Neutralize electrostatic chargebytouching
hand and all toolson an unpainted unitsurface,
suchas thegas valve orblowerdeck,beforeper-
forming any service procedure.
ELECTROSTATIC DISCHARGE(ESD)
Precautions and Procedures
b-ElectronicIgnition
Onacall forheat the SureLightcontrolmonitorsthe com-
bustion airinducerproveswitch.The controlwill notbegin
theheatingcycleif theproveswitchisclosed (by-passed).
Oncethe proveswitchisdetermined to be open, the com-
bustion airinducerisenergized.When the differential in
the proveswitchisgreatenough, the proveswitchcloses
and a 15-second pre-purge begins. If the proveswitchis
notproven within 2-1/2minutes, the controlgoesinto
Watchguard-PressureSwitchmode fora 5-minutere-set
period.
NOTE-The G24Mfurnacecontainselectronic com-
ponentsthatare polarity sensitive.Makesurethat the
furnaceiswired correctlyand isproperlygrounded.
Afterthe 15-second pre-purge period, the SureLightigni-
torwarmsup for20 secondsafterwhichthe gas valve
opensfora4-secondtrialforignition.The ignitorstaysen-
ergized forthe firstsecond of the 4-second trial.G24M
unitswith 63K89,24L85 or56L83: the ignitorstays ener-
gizedthefirstsecondofthe4secondtrial.G24Munitswith
board 97L48:ignitorstays energized during the 4-second
trialuntilflameissensed.Ifignitionisnotprovedduringthe
4-secondperiod,thecontrolwilltryfourmoretimeswithan
interpurge and warm-up time between trialsof35 sec-
onds.Afteratotaloffivetrialsforignition (including the ini-
tialtrial), the controlgoesintoWatchguard-FlameFailure
mode.Aftera60-minuteresetperiod,thecontrolwillbegin
the ignition sequence again.
The SureLightcontrolboard hasan added featurethat
prolongsthe life of the ignitor.Afterasuccessful ignition,
theSureLightcontrolutilizeslesspowertoenergizetheig-
nitoronsuccessivecallsforheat. The controlcontinuesto
rampdownthe voltage totheignitoruntil itfindsthe lowest
amountofpowerthatwill provideasuccessful ignition.
Thisamountofpowerisusedfor255 cycles.Onthe 256th
callforheat, the controlwillagainramp down until thelow-
estpowerisdetermined and the cycle beginsagain.
c-Fan TimeControl
The fan on time of45 secondsisnotadjustable.Fan off
time(timethat the bloweroperatesafterthe heatdemand
hasbeen satisfied)can be adjusted byflipping the dip
switcheslocated on the SureLightintegrated control.The
unitis shipped withafactoryfan off setting of90 seconds.
Fan off timewill affectcomfortand isadjustabletosatisfy
individualapplications.See figure 8.
NOTE—If fan “off”timeis set too low,residualheatin
heatexchangermay cause primarylimitS10 totripre-
sulting infrequentcycling ofblower. If thisoccurs,ad-
justblowertolongertimesetting.
FIGURE8
FAN-OFF TIMEADJUSTMENT
To adjust fan-off timing, flip dipswitchto desired setting.
60sec.90sec.120sec.180sec.