Lennox G43UF SERIES Installation and operation manual

Page 1 ©2004 Lennox Industries Inc.
Litho U.S.A.
Corp. 0416−L4 G43UF
Service Literature Revised 2−2006
G43UF SERIES UNITS
G43UF series units are high−efficiency gas furnaces
manufactured with Lennox DuralokPlustaluminized
steel clamshell−type heat exchangers, with a stainless steel
condensing coil. G43UF units are available in heating in-
put capacities of 44,000 to 132,000 Btuh (13 to 38.6 kW) and
cooling applications from 2 through 5 tons (7.0 through 17.6
kW). Refer to Engineering Handbook for proper sizing.
Units are factory equipped for use with natural gas. A kit is
available for conversion to LPG operation. All G43UF
units are equipped with a hot surface ignition system. The
gas valve is redundant to assure safety shut−off as re-
quired by C.S.A.
The heat exchanger, burners and manifold assembly can be
removed for inspection and service. The maintenance section
gives a detailed description on how this is done.
Information contained in this manual is intended for use by
qualified service technicians only. All specifications are sub-
ject to change. Procedures outlined in this manual are pre-
sented as a recommendation only and do not supersede or
replace local or state codes.
WARNING
Electric shock hazard. Can cause injury
or death. Before attempting to perform
any service or maintenance, turn the
electrical power to unit OFF at discon-
nect switch(es). Unit may have multiple
power supplies.
Table of Contents
General 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Specifications 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Blower Performance Data 4. . . . . . . . . . . . . . . . . . . . . .
I−Unit Components 9. . . . . . . . . . . . . . . . . . . . . . . . . . . .
II Placement and Installation 18. . . . . . . . . . . . . . . . . . . .
III−Start−Up 31. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IV−Heating System Service Checks 32. . . . . . . . . . . . . .
V−Typical Operating Conditions 35. . . . . . . . . . . . . . . . .
High Altitude 35. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VI−Maintenance 37. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VII−Wiring and Sequence of Operation 39. . . . . . . . . . .
VIII−Troubleshooting 49. . . . . . . . . . . . . . . . . . . . . . . . . . .
IMPORTANT
Improper installation, adjustment, alteration, service
or maintenance can cause property damage, person-
al injury or loss of life. Installation and service must
be performed by a qualified installer, service agency
or the gas supplier.
WARNING
Sharp edges.
Be careful when servicing unit to avoid sharp edges
which may result in personal injury.

Page 2
SPECIFICATIONS
Gas
Heating
Performance
ModelNo. G43UF
−24B−045
G43UF
−24B−070
G43UF
−36B−070
G43UF
−36C−090
G43UF
−36C−090H
Canada Only
Performance
Input− Btuh (kW) 44,000 (12.9) 66,000 (19.3) 66,000 (19.3) 88,000 (25.8) 88,000 (25.8)
Output− Btuh (kW) 41,000 (12.0) 60,700 (17.8) 62,000 (18.2) 82,000 (24.0) 81,000 (23.7)
1AFUE 92.1% 90.0% 92.1% 92.1% 90.0%
California Seasonal Efficiency 82.7% 84.2% 85.1% 85.2% 84.2%
Highstatic(CSA)− in.w.g. (Pa) .50 (124) .50 (124) .50 (124) .50 (124) .50 (124)
Temperature rise range − _F (_C) 30 − 60 (18 − 36) 50 − 80 (28 −
44)
40 − 70 (22 −
39)
40 − 70 (22 −
39)
50 − 80 (28 −
44)
Connections
in
2Intake Pipe (PVC) 2 2 2 2 2
in. 2Exhaust Pipe (PVC) 2 2 2 2 2
Condensate Drain Trap (PVC pipe) − i.d. 1/2 1/2 1/2 1/2 1/2
with field supplied (PVC coupling) − o.d. 3/4 3/4 3/4 3/4 3/4
hose with hose clamp − i.d. x o.d. 1−1/4 x 1 1−1/4 x 1 1−1/4 x 1 1−1/4 x 1 1−1/4 x 1
GaspipesizeIPS 1/2 1/2 1/2 1/2 1/2
Indoor
Blower
Wheel nominal diameter x
width −in. (mm)
10 x 7
(254 x 178)
10 x 7
(254 x 178)
10 x 8
(254 x 203)
10 x 8
(254 x 203)
10 x 8
(254 x 203)
Motoroutput − hp (W) 1/5 (149) 1/5 (149) 1/3 (249) 1/3 (249) 1/3 (249)
Tons(kW) ofadd-oncooling 1.5 − 2 (5.3 − 7.0) 1.5 − 2 (5.3 −
7.0)
2 − 3 (8.8 − 10.5) 2 − 3 (7.0 − 10.5) 2 − 3 (7.0 − 10.5)
ShippingData lbs. (kg) − 1 package 132 (60) 141 (64) 146 (66) 162 (74) 162 (74)
Electricalcharacteristics 120 volts − 60 hertz − 1 phase (less than 12 amps)
SPECIFICATIONS
Gas
Heating
Performance
ModelNo. G43UF
−48C−090
G43UF
−48C−110
G43UF
−48C−110H
Canada Only
G43UF
−60C−110
G43UF
−60D−135
Performance
Input− Btuh (kW) 88,000 (25.8) 110,000
(32.2)
110,000
(32.2)
110,000
(32.2)
132,000
(38.7)
Output− Btuh (kW) 82,000 (24.0) 103,000
(30.2)
101,000
(29.6)
103,000
(30.2)
123,000
(36.0)
1AFUE 92.1% 92.1% 90.0% 92.1% 92.1%
California Seasonal Efficiency 85.5% 86.2% 84.7% 85.6% 86.0%
Highstatic(CSA)− in.w.g. (Pa) .50 (124) .50 (124) .50 (124) .50 (124) .50 (124)
Temperature rise range − _F (_C) 40 − 70 (22 − 39) 45 − 75 (27− 45) 50 − 80 (28 − 44) 40 − 70 (22− 39) 45 − 75 (27− 45)
Connections
in
2Intake Pipe (PVC) 2 2 2 2 3
in. 2Exhaust Pipe (PVC) 2 2 2 2 3
Condensate Drain Trap (PVC pipe) − i.d. 1/2 1/2 1/2 1/2 1/2
with field supplied (PVC coupling) − o.d. 3/4 3/4 3/4 3/4 3/4
hose with hose clamp − i.d. x o.d. 1−1/4 x 1 1−1/4 x 1 1−1/4 x 1 1−1/4 x 1 1−1/4 x 1
GaspipesizeIPS 1/2 1/2 1/2 1/2 1/2
Indoor
Blower
Wheelnominaldiameter
xwidth −in. (mm)
10 x 10
(254 x 254)
10 x 10
(254 x 254)
10 x 10
(254 x 254)
11−1/2 x 10
(292 x 229)
11−1/2 x 10
(292 x 229)
Motoroutput − hp (W) 1/2 (373) 1/2 (373) 1/2 (373) 1 (746) 1 (746)
Tons(kW) ofadd-oncooling 3 − 4 (10.5 − 14) 3 − 4 (10.5 − 14) 3 − 4 (10.5 − 14) 4 − 5 (14 − 17.5) 4 − 5 (14 − 17.5)
ShippingData lbs. (kg) − 1 package 168 (76) 178 (81) 178 (81) 186 (84) 203 (92)
Electricalcharacteristics 120 volts − 60 hertz − 1 phase (less than 12 amps)
NOTE − Filters and provisions for mounting are not furnished and must be field provided.
1−Annual Fuel Utilization Efficiency based on DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherized furnaces.
2Determine from venting tables proper exhaust pipe size and termination kit required.

Page 3
OPTIONAL ACCESSORIES − MUST BE ORDERED EXTRA
B" Width Models C" Width Models D" Width Models
FILTER KITS
1Air Filter and
Rack Kit
Side Return Single 44J22 44J22 44J22
Rack Kit Ten Pack 66K63 66K63 66K63
Size of filter − in. (mm) 16 x 25 x 1
(406 x 635 x 25)
16 x 25 x 1
(406 x 635 x 25)
16 x 25 x 1
(406 x 635 x 25)
EZ Filter Base Catalog No. − Ship. Wt. − lbs. (kg) 73P56 − 7 (3) 73P57 − 8 (4) 73P58 − 10 (5)
Size of field provided filter − in.
(mm)
16 x 25 x 1
(406 x 635 x 25)
20 x 25 x 1
(508 x 635 x 25)
24 x 24 x 1
(610 x 610 x 25)
CABINET ACCESSORIES
Return Air Base 76M88 74M74 74M75
CONDENSATE DRAIN KITS
Condensate Drain Heat Cable 6 ft. (1.8 m) 26K68 26K68 26K68
24 ft. (7.3 m) 26K69 26K69 26K69
50 ft. (15.2 m) 26K70 26K70 26K70
Heat Cable Tape Fiberglass − 1/2 in. x 66 ft. 39G04 39G04 39G04
Aluminum foil − 2 in. x 60 ft. 39G03 39G03 39G03
Condensate Trap Alternate Location Kit − Up−Flow Only 76M20 76M20 76M20
CONTROLS
Twinning Kit 15L38 15L38 15L38
TERMINATION KITS − See Installation Instructions for specific venting information.
Termination Kits
Direct Vent
Concentric 1−1/2 in. (38 mm) 71M80 − − − − − −
Direct Vent
A
pp
lications 2 in. (51 mm) − − − 69M29 − − −
Applications
Only 3 in. (76 mm) − − − 60L46 60L46
Wall − Close
Couple
2 in. (51 mm) 22G44 − − − − − −
Couple 3 in. (76 mm) 44J40 44J40 44J40
Close Couple WTK − 2 in. (51 mm) 30G28 − − − − − −
3 in. (76 mm) 81J20 81J20 81J20
2Termination
Kits Direct or
Roof 2 in. (51 mm) 15F75 15F75 15F75
Kits − Direct or
Non−Direct Vent Wall − Wall Ring
Kit
2 in (51 mm) 15F74 15F74 315F74
Roof Termination Flashing Kit − Direct or Non−Direct
Vent − Contains two flashings.
44J41 44J41 44J41
1Cleanable polyurethane frame type filter.
2Kits contain enough parts for two, non−direct vent installations.
3Non−direct vent only.
GAS HEAT ACCESSORIES
Input
Model No
1High Altitude
Orifice Kit
Natural Gas Only
High Altitude Pressure
Switch Kit
LPG/Propane Kit
Input Model No. Natural Gas Only 4501−7500 ft.
(1372−2286 m)
7501−10,000 ft.
(2286−3048 m)
0−7500 ft.
(0−2286 m)
7501−10,000 ft.
(2286−3048 m)
−045 G43UF 59M16 − − − 95M22 83M74 83M75
−045−1 to −6 G43UF 59M16 − − − 56M06 83M74 83M75
−070 G43UF 59M16 56M05 56M06 83M74 83M75
−070−1 to −6 G43UF 59M16 − − − 56M06 83M74 83M75
−090 G43UF 59M16 75M20 56M07 83M74 83M75
−110 G43UF 59M16 75M20 56M07 83M74 83M75
−135 G43UF 59M16 56M04 60M35 83M74 83M75
1Required for proper operation at altitudes from 7501 to 10,000 ft. (2286 to 3048 m).

Page 4
BLOWER/WATTS DATA
G43UF−24B−045−1, −3 PERFORMANCE
External
Static
Air Volume / Watts at Different Blower Speeds
S
tatic
Pressure High Medium Low
in.
w.g. Pa cfm L/s Watts cf
mL/s Watts cf mL/s Watts
0.00 0 975 460 380 870 410 340 720 340 285
0.10 25 935 440 365 855 400 335 710 335 280
0.20 50 910 430 360 830 390 325 680 320 270
0.30 75 870 410 345 795 375 310 655 310 260
0.40 100 825 390 330 760 360 300 630 295 255
0.50 125 760 360 315 715 335 285 610 290 250
0.60 150 725 340 310 675 320 280 580 275 235
0.70 175 680 320 295 630 300 265 545 260 230
0.80 200 620 290 285 575 270 255 495 235 220
0.90 225 555 260 270 520 245 245 425 200 205
G43UF−24B−070−1, −3 PERFORMANCE
External
Static
Air Volume / Watts at Different Blower Speeds
S
tatic
Pressure High Medium Low
in.
w.g. Pa cfm L/s Watts cfm L/s Watts cfm L/s Watts
0.00 25 1020 480 380 905 430 345 740 350 280
0.10 25 985 465 370 890 420 330 730 345 270
0.20 50 945 445 355 860 405 325 705 330 265
0.30 75 905 430 345 830 390 315 690 325 260
0.40 100 860 405 330 790 370 300 660 310 250
0.50 125 810 380 320 750 355 290 630 300 240
0.60 150 740 350 305 710 335 280 590 280 230
0.70 175 700 330 295 650 305 265 550 260 220
0.80 200 635 300 280 590 280 255 495 235 210
0.90 225 555 260 265 530 250 235 425 200 195
NOTES − All air data is measured external to unit with1 in. foam filter (not furnished − field provided).
Air volume based on bottom air return air. Actual air volume may vary on side return air applications.
G43UF−24B−045−4 PERFORMANCE (Less Filter)
External Static Air Volume / Watts at Different Blower Speeds
External
Static
Pressure High Medium−High Medium−Low Low
in. w.g. Pa cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts
0.00 0 1125 530 425 900 425 360 745 350 295 690 325 265
0.10 25 1115 525 410 905 425 350 760 360 285 695 330 260
0.20 50 1090 515 395 895 420 335 755 355 280 685 325 255
0.30 75 1060 500 380 880 415 325 740 350 270 675 320 250
0.40 100 1020 480 365 860 405 315 720 340 260 665 315 240
0.50 125 970 460 345 835 395 300 700 330 255 640 300 230
0.60 150 920 435 335 795 375 290 665 315 240 600 285 220
0.70 175 860 405 315 730 345 270 620 295 230 565 265 215
0.80 200 760 360 295 665 315 250 560 265 215 510 240 200
0.90 225 675 320 275 585 275 230 495 235 200 500 190 175
G43UF−24B−070−4 PERFORMANCE (Less Filter)
External Static Air Volume / Watts at Different Blower Speeds
External
Static
Pressure High Medium−High Medium−Low Low
in. w.g. Pa cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts
0.00 01115 525 435 875 415 360 720 340 290 665 315 255
0.10 25 1115 525 425 865 410 350 725 340 285 670 315 255
0.20 50 1100 520 415 870 410 335 730 345 280 665 315 250
0.30 75 1080 510 400 870 410 330 725 340 270 655 310 240
0.40 100 1050 495 385 855 405 320 715 335 265 645 305 240
0.50 125 1010 475 365 835 395 310 695 330 255 625 295 230
0.60 150 980 460 355 810 380 295 675 320 250 600 285 225
0.70 175 930 440 340 770 365 285 640 300 235 565 265 215
0.80 200 855 405 320 720 340 270 585 275 220 520 245 200
0.90 225 770 365 295 650 305 250 525 245 205 465 220 190
NOTES − All air data is measured external to unit without filter (not furnished − field provided).
Air volume based on bottom air return air. Actual air volume may vary on side return air applications.

Page 5
BLOWER/WATTS DATA
G43UF−36B−070 PERFORMANCE (Less Filter)
External Static Air Volume / Watts at Different Blower Speeds
External
Static
Pressure High Medium−High Medium−Low Low
in. w.g. Pa cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts
0.00 0 1640 775 660 1415 665 575 1160 545 485 1005 475 410
0.10 25 1600 755 635 1395 660 550 1160 545 460 1000 470 385
0.20 50 1540 725 605 1370 650 525 1160 545 445 995 470 375
0.30 75 1495 705 580 1345 635 505 1145 540 425 990 465 365
0.40 100 1420 670 545 1275 605 480 1125 530 395 965 455 345
0.50 125 1360 640 525 1245 590 450 1080 510 375 945 445 325
0.60 150 1275 600 490 1165 550 410 1025 485 350 900 425 305
0.70 175 1170 555 465 1085 515 385 965 430 335 860 405 295
0.80 200 1080 510 440 1010 475 360 865 410 310 775 365 270
0.90 225 945 445 400 840 395 320 765 360 275 710 335 245
NOTES − All air data is measured external to unit without filter (not furnished − field provided).
Air volume based on bottom air return air. Actual air volume may vary on side return air applications.
G43UF−36C−090(H) PERFORMANCE (Less Filter)
External Static Air Volume / Watts at Different Blower Speeds
External
Static
Pressure High Medium−High Medium−Low Low
in. w.g. Pa cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts
0.00 0 1630 770 745 1360 640 635 1125 530 540 975 460 440
0.10 25 1620 765 715 1365 645 610 1160 545 515 1000 470 430
0.20 50 1590 750 680 1365 645 580 1160 545 495 990 465 405
0.30 75 1550 730 655 1355 640 565 1170 550 475 985 465 395
0.40 100 1520 715 630 1330 630 545 1160 545 460 980 460 380
0.50 125 1465 690 605 1300 615 515 1140 540 440 960 455 360
0.60 150 1415 670 570 1250 590 490 1095 515 420 940 445 350
0.70 175 1350 635 545 1215 575 470 1065 500 400 905 425 335
0.80 200 1260 595 510 1140 540 440 1005 475 375 850 400 310
0.90 225 1165 550 475 1035 485 395 900 425 335 730 345 285
NOTES − All air data is measured external to unit without filter (not furnished − field provided).
Air volume based on bottom air return air. Actual air volume may vary on side return air applications.
G43UF−48C−090 PERFORMANCE (Less Filter)
External Static Air Volume / Watts at Different Blower Speeds
External
Static
Pressure High Medium−High Medium−Low Low
in. w.g. Pa cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts
0.00 0 2180 1030 930 1835 865 790 1520 715 630 1280 605 510
0.10 25 2135 1005 885 1825 860 750 1510 710 610 1275 600 495
0.20 50 2085 985 840 1810 855 720 1505 710 580 1270 600 475
0.30 75 2030 955 800 1775 835 685 1500 705 565 1265 595 460
0.40 100 1940 915 760 1735 820 650 1480 700 535 1250 590 440
0.50 125 1865 880 725 1660 785 600 1430 675 505 1215 575 425
0.60 150 1740 820 670 1590 750 575 1380 650 475 1175 555 410
0.70 175 1645 775 640 1475 695 520 1290 610 450 1105 520 375
0.80 200 1540 725 600 1340 630 465 1175 555 405 1020 480 355
0.90 225 1335 630 540 1170 555 440 1070 505 375 950 450 330
NOTES − All air data is measured external to unit without filter (not furnished − field provided).
Air volume based on bottom air return air. Actual air volume may vary on side return air applications.

Page 6
BLOWER/WATTS DATA
G43UF−48C−110 PERFORMANCE (Less Filter)
External Static Air Volume / Watts at Different Blower Speeds
External
Static
Pressure High Medium−High Medium−Low Low
in. w.g. Pa cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts
0.00 0 2160 1020 880 1880 890 755 1490 705 602 1235 580 485
0.10 25 2100 990 850 1855 875 730 1480 700 585 1230 580 475
0.20 50 2035 960 805 1815 860 690 1475 695 560 1225 580 460
0.30 75 1965 925 750 1755 830 650 1475 695 545 1220 575 445
0.40 100 1885 890 725 1715 810 625 1465 690 510 1215 575 430
0.50 125 1780 840 680 1630 770 580 1420 670 490 1150 540 400
0.60 150 1690 800 660 1550 735 550 1360 640 460 1110 525 380
0.70 175 1575 745 620 1410 665 505 1210 570 405 1035 490 350
0.80 200 1375 650 550 1230 580 450 1125 530 380 970 460 325
0.90 225 1225 580 520 1120 530 415 1050 495 365 885 420 310
NOTES − All air data is measured external to unit without filter (not furnished − field provided).
Air volume based on bottom air return air. Actual air volume may vary on side return air applications.
G43UF−60C−110(H) PERFORMANCE (Less Filter) − Single Side Return Air − Air volumes in bold require field fabricated
transition to accommodate 20 x 25 x 1 in. (508 x 635 x 25 mm) air filter in order to maintain proper air velocity.
External Static
P
Air Volume / Watts at Different Blower Speeds
Pressure High Medium−High Medium−Low Low
in. w.g. Pa cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts
0.00 02625 1240 1350 2310 1090 1080 1885 890 885 1515 715 700
0.10 25 2570 1215 1330 2325 1095 1060 1910 900 865 1575 745 700
0.20 50 2410 1135 1305 2285 1080 1035 1930 910 845 1620 765 690
0.30 75 2425 1145 1265 2230 1055 990 1925 905 825 1635 770 675
0.40 100 2335 1100 1220 2175 1025 950 1910 900 810 1640 775 660
0.50 125 2270 1070 1195 2120 1000 935 1895 895 785 1640 775 640
0.60 150 2170 1025 1155 2045 965 885 1860 875 765 1630 770 630
0.70 175 2110 995 1130 1950 920 855 1795 845 730 1590 750 610
0.80 200 2035 960 1090 1885 890 820 1745 825 705 1540 725 580
0.90 225 1900 895 1055 1760 830 780 1665 785 680 1470 695 565
NOTES − All air data is measured external to unit without filter (not furnished − field provided).
G43UF−60C−110 PERFORMANCE (Less Filter) − Bottom Return Air, Side Return Air with Optional RAB Return Air Base,
Return Air from Both Sides or Return Air from Bottom and One Side.
External Static
P
Air Volume / Watts at Different Blower Speeds
Pressure High Medium−High Medium−Low Low
in. w.g. Pa cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts
0.00 0 2720 1285 1385 2410 1135 1090 2055 970 935 1620 765 710
0.10 25 2665 1255 1355 2385 1125 1075 2025 955 885 1730 815 735
0.20 50 2585 1220 1315 2350 1110 1015 2030 955 865 1680 795 690
0.30 75 2505 1180 1275 2290 1080 990 2025 955 840 1695 800 675
0.40 100 2435 1150 1250 2235 1055 940 2030 960 830 1695 800 660
0.50 125 2350 1110 1205 2170 1025 930 1975 930 790 1735 820 665
0.60 150 2255 1065 1185 2100 990 895 1915 905 765 1720 810 650
0.70 175 2160 1020 1150 2005 945 840 1865 880 730 1680 795 635
0.80 200 2020 955 1090 1905 900 825 1810 855 710 1625 765 610
0.90 225 1910 900 1050 1820 860 795 1705 805 675 1540 725 590
NOTES − All air data is measured external to unit without filter (not furnished − field provided).

Page 7
BLOWER/WATTS DATA
G43UF−60D−135 PERFORMANCE (Less Filter) − Single Side Return Air − Air volumes in bold require field fabricated transi-
tion to accommodate 20 x 25 x 1 in. (508 x 635 x 25 mm) air filter in order to maintain proper air velocity.
External Static
Pressure
Air Volume / Watts at Different Blower Speeds
Pressure High Medium−High Medium−Low Low
in. w.g. Pa cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts
0.00 02665 1260 1440 2325 1095 1100 1865 880 890 1410 665 690
0.10 25 2615 1235 1405 2310 1090 1065 1915 905 865 1465 690 685
0.20 50 2530 1195 1370 2280 1075 1055 1925 910 850 1570 740 675
0.30 75 2470 1165 1330 2235 1055 1015 1920 905 825 1590 750 670
0.40 100 2380 1125 1290 2175 1025 985 1910 900 805 1590 750 655
0.50 125 2310 1090 1265 2120 1000 965 1890 890 790 1595 755 645
0.60 150 2200 1035 1230 2055 970 935 1835 865 765 1580 745 630
0.70 175 2120 1000 1190 1970 930 900 1790 845 740 1545 730 605
0.80 200 2025 955 1160 1890 890 875 1720 810 710 1515 715 590
0.90 225 1930 910 1110 1800 850 835 1655 780 685 1440 680 570
NOTES − All air data is measured external to unit without filter (not furnished − field provided).
G43UF−60D−135 PERFORMANCE (Less Filter) − Bottom Return Air, Side Return Air with Optional RAB Return Air Base,
Return Air from Both Sides or Return Air from Bottom and One Side.
External Static
P
Air Volume / Watts at Different Blower Speeds
Pressure High Medium−High Medium−Low Low
in. w.g. Pa cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts
0.00 0 2730 1290 1465 2425 1145 1125 2055 970 915 1560 735 680
0.10 25 2670 1260 1440 2400 1135 1100 2065 975 890 1590 750 675
0.20 50 2600 1225 1400 2365 1115 1070 2045 965 865 1620 765 665
0.30 75 2525 1190 1360 2315 1095 1045 2035 960 845 1615 760 655
0.40 100 2445 1155 1325 2260 1065 1015 2020 955 820 1615 760 645
0.50 125 2360 1115 1280 2195 1035 985 1960 925 790 1610 760 635
0.60 150 2290 1080 1255 2130 1005 965 1900 895 755 1600 755 615
0.70 175 2205 1040 1220 2035 960 910 1825 860 730 1570 740 600
0.80 200 2110 995 1195 1945 915 880 1765 830 710 1540 725 580
0.90 225 1970 930 1120 1835 865 830 1680 795 690 1540 725 545
NOTES − All air data is measured external to unit without filter (not furnished − field provided).

Page 8
G43UF PARTS IDENTIFICATION
FIGURE 1
TOP CAP
CABINET
BURNER BOX
ASSEMBLY
SIGHT
GLASS
DuralokPlusTM
HEAT EXCHANGER
ASSEMBLY
CONDENSER COIL
CONTROL BOX
DOOR
INTERLOCK
SWITCH
COLD HEADER
(COLLECTOR)
BOX
COMBUSTION AIR
INDUCER
BLOWER
ACCESS
DOOR
BURNER
ACCESS
PANEL
FLUE
COLLAR
COMBUSTION
AIR PRESSURE
PROVE SWITCH
PRIMARY LIMIT
WARM HEADER
(COLLECTOR)
BOX
GAS VALVE
AND MANIFOLD
BLOWER
ASSEMBLY

Page 9
I−UNIT COMPONENTS
G43UF unit components are shown in figure 1. The com-
bustion air inducer, gas valve and burners can be accessed
by removing the burner access panel. The blower and con-
trol box can be accessed by removing the blower access
door. G43UF units are designed for bottom and side re-
turn air.
A−Make-Up Box (Figure 2)
A field make-up box is provided for line voltage wiring. Line
voltage wiring to unit is routed from the make up box. The
hot" wire is connected to the door switch and then from the
switch to the integrated ignition control. The make−up box
may be installed inside or outside the unit and on the unit left or
right side (right side shown figure 2).
FIGURE 2
INTERIOR MAKE−UP BOX INSTALLATION
MAKE−UP
BOX
Right Side
B−Control Box Components (Figure 3)
Unit transformer (T1) and integrated ignition control (A92)
are located in the control box. In addition, a door interlock
switch (S51) is located in the control box.
FIGURE 3
DOOR INTERLOCK
SWITCH (S51)
INTEGRATED IGNITION
CONTROL BOARD
(A92)
TRANSFORMER
(T1)
1. Transformer (T1)
A transformer located in the control box provides power to
the low voltage section of the unit. The transformers on all
models are rated at 40VA with a 120V primary and 24V
secondary.
2. Door Interlock Switch (S51)
A door interlock switch rated 14A at 120VAC is located on
the control box. The switch is wired in series with line volt-
age. When the blower door is removed the unit will shut
down.
3. SureLight®Control 32M88 (A92)
G43UF−1 Units
WARNING
Shock hazard.
Disconnect power before servicing. Control is
not field repairable. If control is inoperable, sim-
ply replace entire control.
Can cause injury or death. Unsafe operation will
result if repair is attempted.
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 techni-
cian at the same electrostatic potential. Neutral-
ize electrostatic charge by touching hand and all
tools on an unpainted unit surface, such as the
gas valve or blower deck, before performing any
service procedure.
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
The SureLight ignition system consists of ignition control
board 32M88 (figure 6 with control terminal designations
in table 3), ignitor (figure 9) and sensor (figure 10). Control
board 32M88 and ignitor work in combination to ensure
furnace ignition and ignitor durability. The control board
controls all major furnace operations. The control board
also features two green LED lights (DS1 and DS2) for
troubleshooting and two accessory terminals rated at (1)
one amp. Tables 1 and 2 show jack plug terminal designa-
tions. See table 4 for troubleshooting diagnostic codes.
The SureLight ignitor is made of durable silicon−nitride. Ig-
nitor longevity is also enhanced by voltage ramping by the
control board. The control board finds the lowest ignitor
temperature which will successfully light the burner, thus
increasing the life of the ignitor.

Page 10
TABLE 1
SureLight BOARD J156 (J2) TERMINAL
DESIGNATIONS
PIN # FUNCTION
1Combustion Air Inducer Line
2Ignitor Line
3Combustion Air Inducer Neutral
4Ignitor Neutral
TABLE 2
SureLight BOARD J58 (J1) TERMINAL
DESIGNATIONS
PIN # FUNCTION
1High Limit Output
2Not Used
324V Line
4Not Used
5Rollout Switch In
624V Neutral
7High Limit Input
8 Ground
9Gas Valve In
10 Pressure Switch Out
11 Rollout Switch Out
12 Gas Valve Out
TABLE 3
TERMINAL DESIGNATIONS
COOL−H 120V HOT Blower Cooling Speed (120VAC)
HEAT−H Blower Heating Speed−(120VAC)
EAC−H Electronic Air Cleaner (120VAC)
HUM−H Humidifier (120VAC)
XFMR−H Transformer (120VAC)
LINE−H Input (120VAC)
LINE−N 120V NEUT Input (Neutral)
HUM−N Humidifier (Neutral)
EAC−N Electronic Air Cleaner (Neutral)
XFMR−N Transformer (Neutral)
CIR−N Blower (Neutral)
PARK Alternate Blower Speeds (dead)
(FLAME SENSE) Flame Sensor
Electronic Ignition (See Figure 5)
On a call for heat the SureLight®control board monitors the
combustion air inducer prove switch. The control will not
begin the heating cycle if the prove switch is closed (by−
passed). Once the prove switch is determined to be open,
the combustion air inducer is energized. When the differen-
tial in the prove switch is great enough, the prove switch
closes and a 15−second pre−purge begins. If the prove
switch is not proven within 2−1/2 minutes, the control goes
into Watchguard−Pressure Switch mode for a 5−minute re−
set period.
After the 15−second pre−purge period, the SureLight ignitor
warms up for 20 seconds during which the gas valve opens
at 19 seconds for a 4−second trial for ignition. The ignitor
stays energized during the 4 second trial until flame is
sensed. If ignition is not proved during the 4−second period,
the control will try four more times with an inter purge and
warm−up time between trials of 35 seconds. After a total of
five trials for ignition (including the initial trial), the control
goes into Watchguard−Flame Failure mode. After a 60−min-
ute reset period, the control will begin the ignition sequence
again.
The SureLight control board has an added feature that pro-
longs the life of the ignitor. After a successful ignition, the
SureLight control utilizes less power to energize the ignitor
on successive calls for heat. The control continues to ramp
down the voltage to the ignitor until it finds the lowest
amount of power that will provide a successful ignition. This
amount of power is used for 255 cycles. On the 256th call
for heat, the control will again ramp down until the lowest
power is determined and the cycle begins again. Each time
120V is removed and then re−applied, the control re−starts
the learning process.
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 setting the dip
switches located on the control board. The unit is shipped
with a factory fan off setting of 90 seconds. For customized
comfort, monitor the supply air temperature once the heat
demand is satisfied. Note the supply air temperature at the
instant the blower is de−energized. Adjust the fan−off delay
to achieve a supply air temperature between 90° − 110° at
the instant the blower is de−energized. (Longer delay times
allow for lower air temperature, shorter delay times allow
for higher air temperature). See figure 4.
FAN-OFF TIME ADJUSTMENT
To adjust fan−off timing, flip dip switch to desired setting.
60sec. 90sec. 120sec. 180sec.
(Black square indicates switch position)
OFF OFFOFF OFF ON
ON
ON
ON
OFF
OFF
OFF
OFF
2
2
2 2
1
1
1
1
FIGURE 4

Page 11
The integrated ignition control board is equipped with two LED lights for troubleshooting. The diagnostic codes are listed
below in table 4.
TABLE 4
DIAGNOSTIC CODES
Make sure to Identify LED’S Correctly..
LED#1
32M88 − DS1 Green
78M47 − DS1 Red
LED #2
32M88 − DS2 Green
78M47 − DS2 Green
DESCRIPTION
SIMULTANEOUS
SLOW FLASH
SIMULTANEOUS
SLOW FLASH
Power on − Normal operation.
Also signaled during cooling and continuous fan.
SIMULTANEOUS
FAST FLASH
SIMULTANEOUS
FAST FLASH Normal operation − signaled when heating demand initiated at thermostat.
SLOW FLASH ON Primary or secondary limit switch open. Limit must close within 3 minutes or
unit goes into 1 hour Watchguard.
OFF SLOW FLASH
Prove switch open.
OR:Blocked inlet/exhaust vent;
OR: Prove switch closed prior to activation of combustion air inducer.
ALTERNATING
SLOW FLASH
ALTERNATING
SLOW FLASH
Watchguard −− burners failed to ignite
OR: limit open more than 3 minutes (control board 32M88 Only)
OR: lost flame sense 5 times in one heating cycle
OR: prove switch opened 5 times in one heating cycle
SLOW FLASH OFF Flame sensed without gas valve energized.
ON SLOW FLASH Rollout switch open. OR: 12-pin connector improperly attached.
ON ON
ON OFF Circuit board failure or control wired incorrectly.
OFF ON
y
FAST FLASH SLOW FLASH Main power polarity reversed. Switch line and neutral.
SLOW FLASH FAST FLASH
Low flame signal. Measures below
Control board 32M88 − 0.18 microamps
Control board 78M47 & 100973−01 − 1.5 microamps
Replace flame sense rod.
ALTERNATING
FAST FLASH
ALTERNATING
FAST FLASH
The following conditions are sensed
Improper main ground (control board 32M88) during the ignitor warm−up period
ONLY Improper main ground (control board 78M47 & 100973−01) continuously
OR: Broken ignitor (control board 32M88)
OR: Open ignitor circuit (control board 32M88)
OR: Line voltage to control below
Control board 32M88 75V
Control board 78M47 & 100973−01 90V
NOTE − Slow flash rate equals 1 Hz (one flash per second). Fast flash rate equals 3 Hz (three flashes per second).
Low flame sense current = SureLight Control Board 32M88 0.16 − 0.17 microamps Ignition Control Board 78M47 & 100973−01 0.5 − 1.4 microamps
FIGURE 5
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉ
ÉÉ
DEMAND
CAI
GAS VALVE
ON
OFF
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉ
ÉÉ
ÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉ
IGNITOR**
15 Sec.
Pre −Purge
20 sec.
Ignitor Warmup
4 Sec.Trial
for Ignition
Post
Purge
5 SEC
*Blower on time will be 45 seconds after gas valve is energized. Blower off time will depend on OFF TIME" Setting.
INDOOR BLOWER
ÉÉÉÉÉÉÉÉÉ
Blower On"
Delay
End of
Heat Demand Blower
Off
Time
** Ignitor on ignition control board 78M47 & 100973−01 equipped units will energize for the first 3 seconds of the 4
second trial, following the ignitor 20 second warm up .

Page 12
SURELIGHT®INTEGRATED CONTROL BOARD
32M88
FIGURE 6
J156
J58
XFMR-N
4. Ignition Control 78M47 & 100973−01 (A92)
G43UF−2 and later units
WARNING
Shock hazard.
Disconnect power before servicing. Control is
not field repairable. If control is inoperable, sim-
ply replace entire control.
Can cause injury or death. Unsafe operation will
result if repair is attempted.
The ignition control system consists of an integrated con-
trol board (figure 8 with control terminal designations in
table 7), ignitor (figure 9) and sensor (figure 10). The con-
trol board and ignitor work in combination to ensure fur-
nace ignition and ignitor durability. The control board con-
trols all major furnace operations. The control board also
features two LED lights (DS1 red and DS2 green) for trou-
bleshooting and two accessory terminals rated at (1) one
amp. The control board also features a (3) amp fuse for
overcurrent protection. Tables 5 and 6 show jack plug ter-
minal designations. See table 4 for troubleshooting diag-
nostic codes. The mini−nitride ignitor is made from a non−
porous, high strength proprietary ceramic material that
provides long life and trouble free maintenance. The con-
trol board continuosly monitors line voltage and maintains
the ignitor power at a consistent level to provide proper
lighting and maximum ignitor life.
TABLE 5
4−Pin Terminal Designation
PIN # FUNCTION
1Combustion Air Inducer Line
2Ignitor Line
3Combustion Air Inducer Neutral
4Ignitor Neutral
TABLE 6
12−Pin Terminal Designations
PIN # FUNCTION
1High Limit Output
2Not Used
324V Line
4Not Used
5Rollout Switch Out
624V Neutral
7High Limit Input
8 Ground
9Gas Valve Common
10 Prove Switch In
11 Rollout Switch In
12 Gas Valve Out
TABLE 7
TERMINAL DESIGNATIONS
120 Volt Hot
COOL Cool Speed
HEAT Heat Speed
PARK Park
PARK Park
EAC Electrconic Air Cleaner
XFMR Transformer
LINE Line
HUM Humidifier
120 Volt Neutral
CIRC Blower
XMFR Transformer
HUM Humidifier
LINE Line
Flame FS Flame Signal
Electronic Ignition (See Figure 5)
On a call for heat the ignition control board monitors the
combustion air inducer prove switch. The control board will
not begin the heating cycle if the prove switch is closed (by−
passed). Once the prove switch is determined to be open,
the combustion air inducer is energized. When the differen-
tial in the prove switch is great enough, the prove switch
closes and a 15−second pre−purge begins. If the prove
switch is not proven within 2−1/2 minutes, the control board
goes into Watchguard−Pressure Switch mode for a 5−min-
ute re−set period.

Page 13
After the 15−second pre−purge period, the ignitor warms up
for 20 seconds during which the gas valve opens at 19 sec-
onds for a 4−second trial for ignition. The ignitor remains
energized for the first 3 seconds during the 4 second trial. If
ignition is not proved during the 4−second period, the con-
trol will try four more times with an inter purge and warm−up
time between trials of 35 seconds. After a total of five trials
for ignition (including the initial trial), the control goes into
Watchguard−Flame Failure mode. After a 60−minute reset
period, the control will begin the ignition sequence again.
The control board has an added feature of ignitor power
regulation to maintain consistent lighting and longer ignitor
life under all line voltage conditions.
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 moving the jumper
to a different setting. The unit is shipped with a factory fan
off setting of 90 seconds. For customized comfort, monitor
the supply air temperature once the heat demand is satis-
fied. Note the supply air temperature at the instant the
blower is de−energized. Adjust the fan−off delay to achieve
a supply air temperature between 90° − 110° at the instant
the blower is de−energized. (Longer delay times allow for
lower air temperature, shorter delay times allow for higher
air temperature). See figure 7.
Board 100973−01 only has a 45 second fan off delay after
cooling demand is met. This timing is factory set and can-
not be adjusted.
FAN-OFF TIME ADJUSTMENT
To adjust fan−off timing, reposition jumper across pins to
achieve desired setting.
FIGURE 7
IGNITION CONTROL BOARD
FIGURE 8
DS2
GREEN
DS1
RED
C−Heating Components
Combustion air inducer (B6), primary limit control (S10),
SureLight ignitor, burners, flame rollout switch (S47), gas
valve (GV1), combustion air prove switch (S18), and clam-
shell heat exchangers are located in the heating compart-
ment. The heating compartment can be accessed by re-
moving the burner access panel.
1. Ignitor (Figure 9)
The SureLight ignitor used on G43UF−1 units, is made of
durable silicon nitride. The board finds the lowest ignitor
temperature which will successfully light the burner, thus
increasing the life of the ignitor. Due to this feature of the
board, voltage cannot be measured. The check ignitor,
measure its resistance. A value of 10.9 to 19.7 ohms indi-
cates a good ignitor.
The ignitor used on G43−2 and later units use a mini−nitride
ignitor made from a proprietary ceramic material. Ignitor
longevity is enhanced by controlling the voltage to the igni-
tor. The check ignitor, measure its resistance. A value of 50
to 450 ohms indicates a good ignitor.

Page 14
FIGURE 9
B"
Ignitor Location
BURNERS FRONT VIEW
MEASUREMENT IS TO I.D.
OF RETENTION RING
BRACKET
Silicon nitride
Mini Nitride
A" B"
.625 .406
.685 .306
A"
IGNITOR TYPE
2. Flame Sensor (Figure 10)
A flame sensor is located on the left side of the burner sup-
port. The sensor is mounted on the bottom burner box plate
and the tip protrudes into the flame envelope of the left−
most burner. The sensor can be removed for service with-
out removing any part of the burners. During operation,
flame is sensed by current passed through the flame and
sensing electrode. The ignition control allows the gas valve
to remain open as long as flame signal is sensed.
NOTE − The G43UF furnace contains electronic com-
ponents that are polarity sensitive. Make sure that the
furnace is wired correctly and is properly grounded.
FIGURE 10
5/16"
3. Primary Limit Control (S10)
Figure 11 shows the primary limit (S10) used on G43UF units
located in the heating vestibule panel. S10 is provided with a
shield on some models (figure 11) and must not be removed.
Note orientation of shield and limit if limit is replaced. When ex-
cess heat is sensed in the heat exchanger, the limit will open.
Once the limit opens, the furnace control energizes the
supply air blower and de−energizes the gas valve. The limit
automatically resets when unit temperature returns to nor-
mal. The switch is factory set and cannot be adjusted.
FIGURE 11
PRIMARY LIMIT LOCATION
limit faces shield
limit shield
090, −110 and
−135 only
4. Burners (Figure 12)
All units use inshot burners. Burners are factory set and do not
require adjustment. Burners can be removed as an assembly
for service. Burner maintenance and service is detailed in the
MAINTENANCE section of this manual. Each burner uses
an orifice which is precisely matched to the burner input. All
G43UF natural gas units are fitted with .089" sized orifices.
See table 20 or SPECIFICATIONS" tables for LP kits and
high altitude. The orifice is threaded into the burner man-
ifold.
The burner is supported by the orifice and will easily slide off
for service. A flame retention ring in the end of each burner
maintains correct flame length and shape and keeps the flame
from lifting off the burner head. In addition, the burner entrance
to each clamshell is fitted with a corbel cup (orifice) used to
direct the flow of combustion products.
NOTE − Do not use thread-sealing compound on the ori-
fices. Thread-sealing compound may plug the orifices.

Page 15
FIGURE 12
5/16"
BURNER DETAIL TOP VIEW
ignitor
5. Clamshell Heat Exchanger
G43UF units use an aluminized steel primary and stain-
less steel secondary heat exchanger assembly. Heat is
transferred to the air stream from all surfaces of the heat
exchanger. The shape of the heat exchanger ensures
maximum efficiency.
The combustion air inducer pulls fresh air through the air
intake box. This air is mixed with gas in the burner venturi
and at the corbel orifices. The gas / air mixture is then
burned at the entrance of each clamshell. Combustion
gases are then pulled through the primary and secondary heat
exchangers and exhausted out the exhaust vent pipe.
6. Backup Secondary Limit Control (S113)
(G43UF−090, 110, 135 only)
Backup secondary limit control S113 is a N.C. auto−reset
switch located on the combustion air inducer. S113 acts as
a backup to primary limit S10 in the event of an indoor blow-
er failure. S113 contacts open when temperature on the
CAI reaches 142°.
7. Flame Rollout Switches (S47)
Flame rollout switches S47 are SPST N.C. high temperature
limits located on each side of the burner box assembly (see
figure13). S47 is wired to the burner ignition control A92.
When either of the switches sense flame rollout (indicat-
ing a blockage in the combustion passages), the flame
rollout switch trips, and the ignition control immediately
closes the gas valve. Switch S47 in all G43UF units is fac-
tory preset to open at 250_F + 12_F (121_C + 6.7_C) on a
temperature rise. All flame rollout switches are manual reset.
FIGURE 13
BURNER BOX ASSEMBLY
ROLLOUT SWITCH
(each side)
8. Gas Valve (GV1)
The G43UF uses a gas valve manufactured by Honeywell or
White Rodgers (see figure 14 ). The valves are internally re-
dundant to assure safety shut-off. If the gas valve must be re-
placed, 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 con-
nected to wires from the ignition control. 24V applied to the
terminals opens the valve.
Inlet and outlet pressure taps are located on the valve. A
manifold adjustment screw is also located on the valve.
An LPG changeover kit is available. See table 20. For
units equipped with the Honeywell VR205 valve, the kit
includes a low pressure switch that must be installed in
the valve as shown in figure 14.
The burner box is sealed and operates under a negative
pressure. A pressure hose is connected from the burner
box to the gas valve. The gas valve senses the pressure in
the burner box and changes gas valve outlet (manifold)
pressure based on changes in the burner box pressure.
The intent is to compensate for different vent configura-
tions which can greatly affect the rate of the unit.
IMPORTANT
The White Rodgers 36G gas valve (figure 14) is
equipped with pressure posts for measuring supply
and manifold pressures. The posts provide built−in
hose connections and have an integral 3/32" Allen−
head screw. Rotate the screw counterclockwise one
full turn to permit pressure measurement. Reseat the
screw (rotate one full turn clockwise) after measure-
ments have been taken to prevent gas leakage.

Page 16
FIGURE 14
HONEYWELL VR8205 SERIES GAS VALVE
WHITE RODGERS 36G SERIES GAS VALVE
GAS VALVE SHOWN IN OFF POSITION
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
MANIFOLD PRESSURE
OUTLET POST
LINE PRESSURE
INLET POST
REFERENCE
TO BURNER
BOX
MANIFOLD
PRESSURE
OUTLET
INLET
PRESSURE
PORT WITH
INLET TAP
FITTING
PRESSURE
SWITCH
(LP ONLY)
ON
OFF
BARBED
FITTING
HONEYWELL VR8205 SERIES GAS VALVE
(With On/Off Switch)
GAS VALVE ON/OFF SWITCH SHOWN IN ON POSITION
MANIFOLD
PRESSURE
OUTLET
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
(under cap)
LINE PRESSURE
INLET POST
9. Combustion Air Inducer (B6)
& Cold End Header Box
All G43UF units use a combustion air inducer to move air
through the burners and heat exchanger during heating
operation. The blower uses a shaded pole 120VAC mo-
tor. The motor operates during all heating operation and is
controlled by burner ignition control A3. Blower operates
continuously while there is a call for heat. The burner igni-
tion control will not proceed with the ignition sequence until
combustion air inducer operation is sensed by the proving
switches.
The CAI is installed on the cold end header box. The cold
end header box is a single piece made of hard plastic.
The box has an internal channel where the combustion
air inducer creates negative pressure at unit start up. The
channel contains an orifice used to regulate flow created
by the CAI. The box has pressure taps for the CAI prove
switch hoses. The prove switch measure the pressure
across the CAI orifice or difference in the channel and the
box. A window is provided on the bottom right hand side
of the box to indicate orifice size. See figures 15 and 17.
See table 8 for orifice size per unit. If replacement is
necessary the gaskets used to seal the box to the
vestbule panel and the CAI to the box, must also be
replaced.
WARNING
CARBON MONOXIDE POISONING HAZARD
Do not install a header box designed for the G51 or
G61 furnace onto a G43 furnace. Header boxes for
G51 and G61 furnaces are equipped with open
drain ports in the upper corners of the box, which
allow bypass of the proper flow of combustion air
to the burners. Differences in header box are
shown in figure 15.
When replacing a G43 header box, ensure that the
replacement box is equipped with the same orifice
size and number of drain and pressure ports as the
original. G43 header boxes are GRAY in color. G51
and G61 series header boxes are BLACK in color.
TABLE 8
G43UF Unit C.A.I. Orifice Size
−045−1 to −6 .750"
−045−7 and later .703"
−070−7 and later .922"
−070−1 to −6 .969"
−090 1.063"
−110 1.344"
−135 1.625"

Page 17
FIGURE 15
COLD END HEADER BOXES
G43
(gray in color)
G51 / G61
(black in color)
CLOSED DRAIN PORTS
(BOTH SIDES)
PRESSURE
TAPS
OPEN DRAIN PORTS
(BOTH SIDES)
PRESSURE
TAPS
PRESSURE
TAPS
ORIFICE SIZE ID
ORIFICE SIZE ID
ORIFICE
ORIFICE
10. Combustion Air Prove Switch (S18)
G43UF series units are equipped with a differential
prove switch located on the combustion air inducer
housing. See figures 16 and 17. One side of the switch is
gray (negative hose barb) and the other side is black (positive
hose barb). The switches monitor across the CAI orifice to in-
sure proper flow through the heat exchanger.
The switch is a SPST N.O. prove switch electrically con-
nected to the integrated control. The purpose of the switch is
to prevent burner operation if the combustion air inducer is not
moving enough air for proper combustion.
FIGURE 16
PROVE SWITCH (S18)
side view
bracket
terminals
negative (−) barb
gray
positive (+) barb
black
On start-up, the switch senses that the combustion air inducer
is operating. It closes a circuit to the ignition control when
the difference in pressure across the CAI orifice exceeds a
non−adjustable factory setting. If the switch does not suc-
cessfully sense the required differential, the switch can-
not close and the furnace cannot operate. If the flue or
air inlet become obstructed during operation, the switch
senses a loss of pressure differential and opens the circuit to
the ignition control. If the condensate line is blocked, water
will back up into the header box and reduce the pressure dif-
ferential across the switch. The prove switch opens if the dif-
ferential drops below the set point. See table 9.
Checks of pressure differential can aid in troubleshooting.
When measuring the pressure differential, readings should be
taken at the prove switch. Lack of differential usually indicates
problems in the intake or exhaust piping, but may indicate
problems in the heat exchanger, condensing coil, head-
er boxes, combustion inducer or other components.
TABLE 9
Altitude ft
G43UF
0 − 4500 4501 − 7500 7501 − 10000
G43UF
Set Point
(Pa)
SetPoint
(Pa)
Set Point
(Pa)
−045−7
and later 1.10"(274) 1.10" (274) 1.00" (249)
−045−1 to
−6 units .95" (236) .95" (236) .85" (211)
−070−7
and later 1.00"(249) .95" (236) .85" (211)
−070−1 to
−6 units .95" (236) .95" (236) .85" (211)
−090
85
"
(211)
75
"
(186)
65
"
(162)
−110 .
85"
(211)
.
75"
(186)
.
65"
(162)
−135 .65 (162) .55" (137) .45" (112)
*Set point is factory set and non−adjustable
**See table 20 for high altitude kits.
Measuring pressure differential
The differential pressure is the difference in pressure mea-
sured across the cold end header box orifice.
1 − Remove thermostat demand and allow unit to cycle
off.
2 − Install a tee in the negative (−) line and a tee in the positive
(+) line running from the prove switch to the cold end
header box.
3 − Install a manometer with hose from the negative (−)
side of the manometer to the tee installed in the nega-
tive (−) line and with hose from the positive (+) side of
the manometer to the tee in the positive (+) line.
NOTE − Both sides of the cold end header box are negative.
However the (+) port reads less negative pressure than the
(−) port.

Page 18
FIGURE 17
CAI & COLD END HEADER BOX ASSEMBLY
Install tee’s in the
negative line and
positive line then
connect hoses to
manometer.
prove switch orifice size
cold end header box
+
−
4 − Operate unit and observe draft gauge reading. Read-
ings will change as heat exchanger warms.
a. Take one reading immediately after start-up.
b. Take a second reading after unit has reached steady
state (approximately 5 minutes). This will be the pres-
sure differential.
The pressure differential should be greater
than those listed in table 9.
5 − Remove thermostat demand and allow to cycle off.
6 − Remove manometer and tee’s. Reinstall combustion air
sensing hoses to the prove switch.
D−Blower Compartment
Blower motor (B3) and capacitor (C4), are located in the
blower compartment. The blower compartment can be ac-
cessed by removing the blower access panel.
1.Blower Motor (B3) and Capacitor (C4)
All G43UF units use single−phase direct−drive blower mo-
tors. All motors are 120V permanent split capacitor motors
to ensure maximum efficiency. See SPECIFICATIONS table
at the front of this manual for more detail. See motor name-
plate for capacitor ratings.

Page 19
II−PLACEMENT AND INSTALLATION
Table 10 lists the available exhaust termination kits. All Len-
nox vent terminations are PVC or ABS.
TABLE 10
TERMINATION KITS
Vent Pipe Length Equivalency (feet)
UNIT
MODEL
VENT
PIPE
DIA.
(in.)
Outdoor
Exhaust
Accelerator
(Dia. X
Length)
Outdoor
Exhaust
Accelerator
(Dia. X
Length)
1−1/2"
Concen-
tric Kit
2" Con-
centric
Kit
3" Con-
centric
Kit
2" Wall
Plate Kit
3" Wall
Plate Kit
2" Wall
Kit with
Vent Ex-
tension
2" Wall
Ring Kit
1−1/2" X 12" 2" X 12" 71M80 60M29 60L46 22G44 44J40
81J20 30G28 15F74
2 4 Not
Allowed 12 Not Allowed
Not
Allowed 4 4* 4 4
24B−045 2−1/2 5 Not
Allowed 15 Not Allowed
Not
Allowed 5 5* 5 5
24B 045
36B−045 3 7 Not
Allowed 21 Not Allowed
Not
Allowed 7 7* 7 7
4 14 Not
Allowed 42 Not Allowed
Not
Allowed 14 14* 14 14
24Not
Allowed 12 Not Allowed
Not
Allowed 4 4* 4 4
36B−070
2−1/2 5Not
Allowed 15 Not Allowed
Not
Allowed 5 5* 5 5
36B
−
070
38Not
Allowed 24 Not Allowed
Not
Allowed 8 8* 8 8
414 Not
Allowed 42 Not Allowed
Not
Allowed 14 14* 14 14
2Not
Allowed 1Not Allowed 3 3 Not Allowed 1Not Allowed 1**
36C−090 2−1/2 Not
Allowed 2Not Allowed 6 6 Not Allowed 2Not Allowed 2**
36C 090
48C−090 3Not
Allowed 2Not Allowed 6 6 Not Allowed 2Not Allowed 2**
4Not
Allowed 4Not Allowed 12 12 Not Allowed 4Not Allowed 4**
2Not
Allowed 1Not Allowed 3 3 Not Allowed 1Not Allowed 1**
48C−110 2−1/2 Not
Allowed 2Not Allowed 6 6 Not Allowed 2Not Allowed 2***
48C 110
60C−110 3Not
Allowed 2Not Allowed 6 6 Not Allowed 2Not Allowed 2***
4Not
Allowed 4Not Allowed 12 12 Not Allowed 4Not Allowed 4***
60D−135
3Not
Allowed 6Not Allowed
Not
Allowed 15 Not Allowed 6Not Allowed 6***
60D
−
135
4Not
Allowed 10 Not Allowed
Not
Allowed 25 Not Allowed 10 Not Allowed 10***
*Requires field−provided and installed 1−1/2" exhaust accelerator.
**Requires field−provided and installed 2" exhaust accelerator.
***For use only in non−direct vent applications, when snow riser is not required. Requires field−provided and installed 2" exhaust accelera
tor.
***For use only in non−direct vent applications.

Page 20
A−Vent Piping Guidelines
The G43UF can be installed as either a Non−Direct Vent
or a Direct Vent gas central furnace.
NOTE − In Non-Direct Vent installations, combustion air is
taken from indoors and flue gases are discharged outdoors.
In Direct Vent installations, combustion air is taken from out-
doors and flue gases are discharged outdoors.
Intake and exhaust pipe sizing in Direct Vent applications
and exhaust pipe sizing in Non-Direct Vent applications −−
Size pipe according to tables 11, 12 (direct vent) and 13
(non−direct vent). Table 11 lists the minimum equivalent
vent pipe lengths permitted. Tables 12 and 13 list the max-
imum equivalent pipe lengths permitted.
Maximum vent length is defined as:
Total length (linear feet) of pipe,
Plus Equivalent length (feet) of fittings,
Plus Equivalent length (feet) of termination.
NOTE − Include ALL pipe and ALL fittings, both in
doors and outdoors.
Regardless of the diameter of pipe used, the standard roof
and wall terminations described in section Exhaust Piping
Terminations should be used. Exhaust vent termination
pipe is sized to optimize the velocity of the exhaust gas as
it exits the termination. Refer to table 14.
NOTE − The exhaust pipe should be offset a minimum of 12
inches to avoid the possibility of water droplets being re-
leased from the exhaust termination. The minimum ex-
haust vent length is 15 ft. Shorter exhaust vent lengths may
result in the discharge of water droplets from the exhaust
termination, in spite of the 12−inch vertical offset.
Each 90° elbow (including those provided with the furnace)
of any diameter is equivalent to 5 feet (1.52m) of vent pipe
of the same diameter. Two 45° elbows are equivalent to
one 90° elbow of the same diameter. One 45° elbow is
equal to 2.5 feet (.76m) of vent pipe of the same diameter.
In some applications which permit the use of several differ-
ent sizes of vent pipe, a combination vent pipe may be
used. Contact the Application Department for assistance in
sizing vent pipe in these applications.
NOTE − The flue collar on all models is sized to accommo-
date 2" Schedule 40 flue pipe. When vent pipe which is
larger than 2" must be used in an upflow application, a 2"
elbow must be applied at the flue collar in order to proper-
ly transition to the larger diameter flue pipe. This elbow
must be added to the elbow count used to determine ac-
ceptable vent lengths. Assign an equivalent feet value to
this elbow according to the larger size pipe being used.
Contact the Application Department for more information
concerning sizing of vent systems which include multiple
pipe sizes.
Use the following steps to correctly size vent pipe diameter.
1 − Determine the vent termination and its corresponding
equivalent feet value according to table 10.
2 − Determine the number of 90° elbows required for both
indoor and outdoor (e.g. snow riser) use. Calculate the
corresponding equivalent feet of vent pipe.
3 − Determine the number of 45° elbows required for both
indoor and outdoor use. Calculate the corresponding
equivalent feet of vent pipe.
4 − Determine the length of straight pipe required.
5 − Add the total equivalent feet calculated in steps 1
through 4 and compare that length to the maximum
values given in table 12 or 13 for the proposed vent
pipe diameter. If the total equivalent length required
exceeds the maximum equivalent length listed in the
appropriate table, evaluate the next larger size pipe.
IMPORTANT
Do not use screens or perforated metal in exhaust
terminations. Doing so will cause freeze−ups and
may block the terminations.
TABLE 11
MINIMUM VENT PIPE LENGTHS
G43UF
MODEL
MIN. EQUIV.
VENT LENGTH EXAMPLE
045, 070,
090
5 ft. plus 2 elbows of 2", 2−1/2", 3"
or 4" diameter pipe
110** 15 ft.* 5 ft. plus 2 elbows of 2−1/2" 3" or 4"
diameter pipe
135*** 5 ft. plus 2 elbows of 3" or 4"
diameter pipe
*Any approved termination may be added to the minimum equivalent length
listed.
**G43UF−48C−110 and G43UF−60C−110 must have 90° street ell (supplied)
installed directly into unit flue collar.
***G43UF−60D−135 must have 3" to 2" reducing ell (supplied) installed directly
into unit flue collar.