Lennox G50UHi Series Installation and operation manual

Page 1 ©2003 Lennox Industries Inc.
Corp. 0304−L4 G50UHi
Service Literature Revised 10−2005
G50UHi Series Units
G50UHi series units are mid−efficiency gas furnaces used
for upflow or horizontal applications only, manufactured
with Lennox Duralok Plus®heat exchangers formed of alu-
minized steel. G50UHi units are available in heating capac-
ities of 66,000 to 154,000 Btuh and cooling applications up
to 5 tons. Refer to Engineering Handbook for proper sizing.
Units are factory equipped for use with natural gas. Kits are
available for conversion to LPG operation. G50UHi model
units are equipped with the Lennox SureLight®silicon ni-
tride ignition system and blower control module. The blower
control module allows the G50Ui to maintain a constant
CFM over a wide range of operating static pressure. All units
use a redundant gas valve to assure safety shut−off as re-
quired by C.S.A.
All specifications in this manual are subject to change. Pro-
cedures outlined in this manual are presented as a recom-
mendation only and do not supersede or replace local 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.
TABLE OF CONTENTS
Introduction 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Specifications 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
High Altitude 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Blower Data 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Parts Identification 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I Unit Components 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
II Installation 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
III Start Up 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IV Heating System Service Checks 17. . . . . . . . . . . . . .
V Typical Operating Characteristics 20. . . . . . . . . . . . . .
VI Maintenance 20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VII Wiring and Sequence of Operation 22. . . . . . . . . . . .
VIII Troubleshooting 28. . . . . . . . . . . . . . . . . . . . . . . . . . .
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
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.
WARNING
Sharp edges.
Be careful when servicing unit to avoid sharp edges
which may result in personal injury.

Page 2
SPECIFICATIONS
Gas
Hti
ModelNo. G50UHi−36A−070 G50UHi−36B−090 G50UHi−48B−090
Heating
Performance Input− Btuh (kW) 66,000 (19.3) 88,000 (25.8) 88,000 (25.8)
Performance
Output− Btuh (kW) 54,100 (15.8) 72,100 (21.1) 72,100 (21.1)
1AFUE 80.0% 80.0% 80.0%
California Seasonal Efficiency 74.8% 75.7% 75.3%
Highstatic (CSA) − in.w.g. (Pa) .50 (124) .50 (124) .50 (124)
Temperature rise range − _F (_C) 40 − 70 (22 − 39) 40 − 70 (22 − 39) 40 − 70 (22 − 39)
Connections Flue − in. (mm) round 4 (102) 4 (102) 4 (102)
GaspipesizeIPS− in. (mm) 1/2 (12.7) 1/2 (12.7) 1/2 (12.7)
Indoor
Blower
Wheelnominaldiameter xwidth −in. (mm) 10 x 8 (254 x 203) 10 x 8 (254 x 203) 10 x 10 (254 x 254)
Blower Motoroutput − hp (W) 1/3 (249) 1/3 (249) 1/2 (373)
Tons(kW) ofadd-oncooling 2 − 3 (7.0 − 10.6) 2 − 3 (7.0 − 10.6) 2 − 4 (7.0 − 14.1)
Shippingweight − 1 package 132 lbs. (60 kg) 146 lbs. (66 kg) 153 lbs (69 kg)
Electricalcharacteristics 120 volts − 60 hertz − 1 phase (less than 12 amps)
OPTIONAL ACCESSORIES − MUST BE ORDERED EXTRA
Filters and
Filter Racks
2Air Filter and
Rack Kit
No & size of fil
Horizontal (end) 87L95 − (1) 14 x 25 x 1 in.
(356 x 635 x 25 mm)
87L96 − (1) 18 x 25 x 1 in.
(457 x 635 x 25 mm)
87L96 − (1) 18 x 25 x 1 in.
(457 x 635 x 25 mm)
No. & size of fil-
ters Side Return − in. (mm) Single 44J22/Ten Pack 66K63
(1) 16 x 25 x 1(406 x 635 x 25) Single 44J22/ Ten Pa c k 66K63 (1) 16 x 25 x 1(406 x 635 x 25) Single 44J22/ Te n P a ck 66K63 (1) 16 x 25 x 1(406 x 635 x 25)
EZ Filter
Base
Catalog Number − Ship. Wt. 73P55 − 6 lbs. (3 kg) 73P56 − 7 lbs. (3 kg) 73P56 − 7 lbs. (3 kg)
Base Dimensions − H x W x D 4 x 14−1/4 x 28−5/8 in.
(102 x 362 x 727 mm)
4 x 17−5/8 x 28−5/8 in.
(102 x 448 x 727 mm)
4 x 17−5/8 x 28−5/8 in.
(102 x 448 x 727 mm)
Number and size of filter (field provided) − in. (mm) 14 x 25 x 1 (356 x 635 x 25) 16 x 25 x 1 (406 x 635 x 25) 16 x 25 x 1 (406 x 635 x 25)
Gas
Accessories
3High Altitude Orifice Kit − Nat. Gas Only 47M82 47M82 47M82
Accessories 4High Altitude
Pressure Switch
Kit
4501−7500 ft.
(1372−2286 m)
56L32 49L90 49L90
7501−10,000 ft. (2286−3048 m) 56L32 15M22 15M22
LPG/Propane Kit 0−7500 ft. (0−2286 m) 45L60 45L60 45L60
7501−10,000 ft. (2286−3048 m) 47M81 47M81 47M81
Horizontal Support Frame Kit − Shipping Weight 56J18 − 18 lbs. (8 kg) 56J18 − 18 lbs. (8 kg) 56J18 − 18 lbs. (8 kg)
Relay Kit 56L68 56L68 56L68
SignatureStatt− Home Comfort Controller 51M26 51M26 51M26
Vent Adaptor − 6 in. 152 (mm) connection size 18M79 − 2 lbs. (1 kg) 18M79 − 2 lbs. (1 kg) 18M79 − 2 lbs. (1 kg)
NOTE − Filters and provisions for mounting are not furnished and must be field provided.
1Annual Fuel Utilization Efficiency based on DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherized furnaces.
2Cleanable polyurethane frame type filter.
3Required for proper operation at altitudes from 7501 to 10,000 ft. (2286 to 3048 m).
4Required for proper operation at altitudes over 4500 ft. (1370 m).

Page 3
SPECIFICATIONS
Gas
Hti
ModelNo. G50UHi−60C−110 G50UHi−60D−135
Heating
Performance Input− Btuh (kW) 110,000 (32.2) 132,000 (38.7)
Performance
Output− Btuh (kW) 89,400 (26.2) 106,900 (31.3)
1AFUE 80.0% 80.0%
California Seasonal Efficiency 73.9% 75.0%
Highstatic (CSA) − in.w.g. (Pa) .50 (124) .50 (124)
Temperature rise range − _F (_C) 30 − 60 (18 − 36) 45 − 75 (25 − 42)
Connections Flue − in. (mm) round 4 (102) 54 (102)
GaspipesizeIPS− in. (mm) 1/2 (12.7) 1/2 (12.7)
Indoor
Blower
Wheelnominaldiameter xwidth −in. (mm) 11−1/2 x 10 (292 x 254) 11−1/2 x 10 (292 x 254)
Blower Motoroutput − hp (W) 1 (746) 1 (746)
Tons(kW) ofadd-oncooling 5 (17.6) 5 (17.6)
Shippingweight − 1 package 175 lbs. (79 kg) 195 lbs. (88 kg)
Electricalcharacteristics 120 volts − 60 hertz − 1 phase (less than 12 amps)
OPTIONAL ACCESSORIES − MUST BE ORDERED EXTRA
Filters and
Filter Bases
2Air Filter and Rack Kit
Number & size of filters
Horizontal (end) − in. (mm) 87L97 (1) 20 x 25 x 1 (508 x 635 x 25) 87L98 (1) 25 x 25 x 1 (635 x 635 x 25)
Filter Bases Number & size of filters
Side Return − in. (mm) Single 44J22 or Ten Pack 66K63
(1) 16 x 25 x 1 (406 x 635 x 25) Single 44J22 or Ten Pack 66K63 (1) 16 x 25 x 1 (406 x 635 x 25)
EZ Filter
Base Catalog Number − Shipping Weight 73P57 − 8 lbs. (4 kg) 73P58 − 10 lbs. (5 kg)
Dimensions − H x W x D − in. (mm) 4 x 21−5/8 x 28−5/8 (102 x 549 x 727) 4 x 24−5/8 x 28−5/8 (102 x 625 x 727)
Number and size of filter (field provided) 20 x 25 x 1 in. (508 x 635 x25 mm) 24 x 24 x 1 in. (610 x 610 x 25 mm)
Gas
Accessories
3High Altitude Orifice Kit − Nat. Gas Only 47M82 47M82
Accessories 4High Altitude
Pressure Switch Kit
4501−7500 ft. (1372−2286 m) 49L90 49L90
Pressure Switch Kit 7501−10,000 ft. (2286−3048 m) 15M22 15M22
LPG/Propane Kit 0−7500 ft. (0−2286 m) 45L60 45L60
p
7501−10,000 ft. (2286−3048 m) 47M81 47M81
Horizontal Support Frame Kit − Shipping Weight 56J18 − 18 lbs. (8 kg) 56J18 − 18 lbs. (8 kg)
Relay Kit 56L68 56L68
SignatureStatt− Home Comfort Controller 51M26 51M26
Vent Adaptor − 6 in. 152 (mm) connection size 18M79 − 2 lbs. (1 kg) 18M79 − 2 lbs. (1 kg)
NOTE − Filters and provisions for mounting are not furnished and must be field provided.
1Annual Fuel Utilization Efficiency based on DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherized furnaces.
2Cleanable polyurethane frame type filter.
3Required for proper operation at altitudes from 7501 to 10,000 ft. (2286 to 3048 m).
4Required for proper operation at altitudes over 4500 ft. (1370 m).
5Flue connection on the unit is 4 in. (102 mm) diameter. Most applications will require 5 in. (127 mm) venting and field supplied 4 x 5 in. (102 x 127 mm) adaptor. See
Venting Tables in the Installation Instructions for detailed information.
HIGH ALTITUDE INFORMATION
All models − Pressure regulator adjustment may be required de-
pending on altitude. See below for proper pressure regulator
setting.
Manifold Pressure (Outlet) in. w.g. (kPa)
ALTITUDE ft. (m)
FUEL 0−4500
(0−1372)
4501−5500
(1373−1676
)
5501−6500
(1677−1981
)
6501−7500
(1982−2286
)
Natural Gas 3.5 (.87) 3.3 (.82) 3.2 (.80) 3.1 (.77)
LPG/Propane 10.0 (2.49) 10.0 (2.49) 10.0 (2.49) 10.0 (2.49)
Pressure switch is factory set. No adjustment is necessary.
All models use the factory installed pressure switch from 0−4500 feet
(0−1370 m).
All models require a High Altitude Pressure Switch Kit if installed at altitudes
above 4500 feet (1372 m).
All natural gas models require a High Altitude Orifice Kit at altitudes of
7500−10,000 feet (2286−3048 m).
See Specifications table for ordering information.

Page 4
BLOWER DATA
JUMPER SELECTION FOR BLOWER CONTROL MODULE
Blower Mode Available Speed
Selector Settings
Factory Default Cool Heat Fan Dehum Ramp
1 2 1
3 O
ff
36A−070
36B−090
48B−090
60C−110
60D−135
36A−070
36B−090
48B−090
60C−110
60D−135
1
3
1
3
4
2
5
6
1
4
5
3
A
B
Off
Cool 1, 1, 3, 4 1, 1, 3, 4 1 1 4 5 7 6 C
Heat 1, 2, 3, 4 2, 3, 4, 5 3 4
Fan 2, 5, 6, 7 2, 5, 6, 7 7 7 Jumper is placed across the two pins to
select the noted speed or ramping profile
Dehumid 3, 4, 5, 6 3, 4, 5, 6 3 3 select the noted speed or ramping profile.
NOTE − Jum
p
er selections are NOT
Ramp Off, A, B, C Off, A, B, C A A
NOTE
Jumper
selections
are
NOT
printed on the Blower Control Module.
G50UHi−36A−070
Jumper Speed Selector
External Static
Pressure Speed 1
Factory Default
Cool
Speed 2 Speed 3
Factory Default
Heat/Dehumid
Speed 4 Speed 5 Speed 6 Speed 7
Factory Default
Fan
in. w.g. Pa cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts
0 0 1290 610 450 1190 565 380 1085 510 330 955 450 260 855 405 210 775 365 185 650 305 135
0.1 25 1295 610 480 1190 560 405 1095 515 345 970 460 290 845 400 225 775 365 190 655 310 145
0.2 50 1300 615 510 1190 560 425 1095 515 370 975 460 305 845 400 240 770 360 205 640 300 150
0.3 75 1285 605 510 1190 560 450 1095 515 385 975 460 320 855 405 260 765 360 220 610 290 160
0.4 100 1220 575 500 1190 560 465 1090 515 405 970 455 335 845 400 275 760 360 235 590 275 175
0.5 125 1210 570 520 1175 555 465 1090 515 420 960 455 350 835 395 285 735 350 245 580 275 185
0.6 150 1165 550 525 1150 540 470 1065 505 450 950 450 375 815 385 305 720 340 260 565 265 200
0.7 175 1125 530 500 1105 520 490 1040 490 430 945 445 380 800 380 325 705 335 280 550 260 210
0.8 200 1065 500 480 1060 500 475 985 465 445 875 415 390 790 375 330 690 325 290 525 250 225
0.9 225 935 440 435 930 440 435 885 420 410 825 390 390 740 350 350 675 320 295 510 240 235
NOTES − All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished − field provided) in place. Also see Filter Air Resistance table.
Air volume based on bottom return air. Actual air volume may vary on side return air applications.
G50UHi−36B−090
Jumper Speed Selector
External Static
Pressure Speed 1
Factory Default
Cool
Speed 2 Speed 3
Factory Default
Heat/Dehumid
Speed 4 Speed 5 Speed 6 Speed 7
Factory Default
Fan
in. w.g. Pa cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts
0 0 1275 600 410 1165 550 335 1045 495 290 940 445 250 860 405 215 780 370 185 665 315 140
0.1 25 1280 605 425 1185 560 365 1075 505 310 965 455 260 850 400 220 780 370 185 670 315 145
0.2 50 1300 615 450 1205 570 390 1090 515 330 970 460 285 865 410 235 785 370 200 665 315 155
0.3 75 1295 610 465 1210 570 410 1095 515 350 980 460 300 865 410 250 780 365 215 645 305 160
0.4 100 1295 610 490 1215 570 435 1100 520 375 985 465 315 865 410 265 775 365 225 625 295 180
0.5 125 1290 610 500 1210 570 455 1095 520 390 985 465 335 860 405 280 770 360 245 610 290 190
0.6 150 1275 605 520 1205 570 470 1090 515 410 975 460 355 855 405 300 760 360 255 595 280 205
0.7 175 1200 565 510 1195 565 475 1090 515 435 965 455 375 840 395 310 745 350 270 580 275 215
0.8 200 1175 555 530 1155 545 500 1065 505 425 965 455 415 830 390 340 730 345 295 560 265 225
0.9 225 1115 525 505 1125 530 500 1030 485 445 920 435 395 790 375 330 715 335 320 550 260 240
NOTES − All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished − field provided) in place. Also see Filter Air Resistance table.
Air volume based on bottom return air. Actual air volume may vary on side return air applications.

Page 5
G50UHi−48B−090
External
Jumper Speed Selector
External
Static
Pressure
Speed 1
Factory Default
Cool
Speed 2 Speed 3
Factory Default
Dehumid
Speed 4
Factory Default
Heat
Speed 5 Speed 6 Speed 7
Factory Default
Fan
in. w.g. Pa cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts
0 0 1800 850 655 1585 750 495 1465 690 420 1345 635 360 1225 575 300 1060 500 230 890 420 170
0.1 25 1795 845 670 1590 750 515 1485 700 455 1365 645 395 1225 580 320 1050 495 235 845 400 175
0.2 50 1755 830 690 1580 745 545 1495 705 490 1375 650 415 1240 585 350 1030 485 255 820 385 185
0.3 75 1710 805 690 1565 740 565 1470 695 500 1370 645 445 1245 585 375 1025 485 285 760 360 190
0.4 100 1605 755 660 1550 730 585 1450 685 525 1355 640 455 1225 580 395 1015 480 300 745 350 210
0.5 125 1610 760 715 1510 715 580 1435 675 540 1340 630 485 1210 570 415 1005 475 330 740 350 225
0.6 150 1550 730 680 1475 695 600 1410 665 570 1325 625 510 1190 560 445 980 465 345 745 350 250
0.7 175 1470 695 640 1430 675 625 1365 645 555 1290 610 500 1170 550 455 965 455 355 715 340 265
0.8 200 1350 635 585 1370 645 615 1315 620 590 1225 575 535 1130 530 470 955 450 370 695 325 285
0.9 225 1220 575 550 1260 595 575 1260 595 575 1195 565 540 1090 515 490 935 440 400 670 315 295
NOTES − All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished − field provided) in place. Also see Filter Air Resistance table.
Air volume based on bottom return air. Actual air volume may vary on side return air applications.
G50UHi−60C−110
External
Jumper Speed Selector
External
Static
Pressure
Speed 1
Factory Default
Cool
Speed 2 Speed 3
Factory Default
Dehumid
Speed 4
Factory Default
Heat
Speed 5 Speed 6 Speed 7
Factory Default
Fan
in. w.g. Pa cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts
0 0 2150 1015 915 1965 925 735 1850 875 640 1695 800 535 1515 715 425 1295 610 315 1000 470 215
0.1 25 2140 1010 935 1960 925 775 1830 865 660 1695 800 565 1535 725 460 1345 635 355 975 460 220
0.2 50 2085 985 930 1960 925 815 1825 860 710 1700 800 595 1545 730 500 1375 650 400 1000 475 240
0.3 75 2085 985 1000 1965 925 855 1825 860 735 1675 790 610 1540 725 520 1375 650 420 1075 505 290
0.4 100 2055 970 1015 1945 920 890 1825 860 775 1680 790 645 1525 720 545 1375 650 455 1075 505 310
0.5 125 2010 950 1025 1895 895 890 1810 855 810 1680 795 690 1515 715 580 1350 635 465 1075 505 335
0.6 150 1950 920 1015 1885 890 965 1795 845 850 1640 775 705 1505 710 605 1335 630 490 1050 495 345
0.7 175 1900 895 1010 1850 875 970 1760 830 865 1630 770 735 1485 700 625 1335 630 530 1010 480 360
0.8 200 1845 870 1025 1790 845 950 1700 800 875 1605 755 755 1460 690 645 1315 620 545 1000 470 385
0.9 225 1740 820 980 1715 810 955 1665 785 915 1570 740 785 1425 670 675 1275 600 570 995 470 420
NOTES − All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished − field provided) in place. Also see Filter Air Resistance table.
Air volume based on side return air. Actual air volume may vary on bottom return air applications.
G50UHi−60D−135
External
Jumper Speed Selector
External
Static
Pressure
Speed 1
Factory Default
Cool
Speed 2 Speed 3
Factory Default
Dehumid
Speed 4
Factory Default
Heat
Speed 5 Speed 6 Speed 7
Factory Default
Fan
in. w.g. Pa cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts cfm L/s Watts
0 0 2160 1020 905 1985 935 735 1910 900 665 1705 805 520 1580 745 460 1290 610 315 1040 490 230
0.1 25 2165 1020 945 1975 930 770 1895 895 695 1725 815 565 1595 750 475 1345 635 350 990 465 220
0.2 50 2115 995 935 1970 930 805 1890 890 730 1710 805 575 1605 755 525 1380 650 385 945 445 225
0.3 75 2055 970 925 1975 935 845 1895 895 770 1705 805 620 1600 755 545 1395 660 425 1010 475 260
0.4 100 2090 985 1015 1960 925 870 1885 890 805 1705 805 650 1590 750 565 1410 665 455 1115 525 330
0.5 125 2065 975 1040 1940 915 895 1865 880 825 1700 800 670 1585 750 590 1380 650 465 1120 530 350
0.6 150 2020 955 1030 1880 885 880 1855 875 865 1685 795 700 1570 740 620 1355 640 490 1105 520 370
0.7 175 1965 925 1040 1880 885 965 1815 855 880 1650 780 725 1550 730 650 1340 630 510 1065 500 375
0.8 200 1910 900 1040 1850 875 960 1760 830 880 1645 775 760 1535 725 670 1340 635 550 1055 500 395
0.9 225 1805 850 975 1785 845 985 1740 820 920 1610 760 785 1500 710 695 1310 620 555 1035 490 430
NOTES − All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished − field provided) in place. Also see Filter Air Resistance table.
Air volume based on side return air. Actual air volume may vary on bottom return air applications.

Page 6
FIGURE 1

Page 7
FIGURE 2
G50UHi PARTS IDENTIFICATION
(HORIZONTAL POSITION)
BLOWER
ACCESS PANEL
HEAT EXCHANGER
ASSEMBLY
BURNER
ASSEMBLY
COMBUSTION AIR
INDUCER
SURELIGHT®CONTROL
BOARD
GAS VALVE
BURNER
ACCESS PANEL
BLOWER ASSEMBLY
PRIMARY LIMIT
BLOWER CONTROL MODULE
FIGURE 3
G50UHi HEATING COMPONENTS

Page 8
I−UNIT COMPONENTS
G50UHi unit components are shown in figures 1, 2 and 3.
The gas valve, combustion air inducer and burners can be
accessed by removing the burner access panel. Electrical
components are in the control box (figure 4) found in the
blower section.
G50UHi units are factory equipped with a bottom return air
panel in place. The panel is designed to be field removed as
required for bottom air return. Markings are provided for side
return air and may be cut out in the field.
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 dis-
charge by putting the furnace, the control and
the technician at the same electrostatic poten-
tial. Neutralize electrostatic charge by touching
hand and all tools on an unpainted unit surface,
such as the gas valve or blower deck, before per-
forming any service procedure.
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
1. Control Transformer (T1)
A transformer located in the control box provides power to
the low voltage section of the unit. Transformers on all
models are rated 40VA with a 120V primary and a 24V sec-
ondary.
2. Door Interlock Switch (S51)
A door interlock switch rated 14A at 125VAC is wired in se-
ries with line voltage. When the blower door is removed the
unit will shut down.
FIGURE 4
CONTROL BOX
G50UHi
SURELIGHT
CONTROL
BOARD
TRANSFORMER
CIRCUIT BREAKER DOOR INTERLOCK
SWITCH

Page 9
INTEGRATED IGNITION CONTROL 97L48
FIGURE 6
J58
J156
TABLE 1
IGNITION CONTROL 97L48 TERMINAL DESIGNATIONS
ACB COOL blower − cooling speed (line voltage)
ACB HEAT blower − heating speed (line voltage)
PARK alternate blower speeds
ACB LOW continuous low speed
ACC accessory terminal (line voltage)
TX line voltage to transformer
HOT 120vac hot
HTG ACC heat only accessory (line voltage)
NEUTRAL 120vac neutral
24VAC HOT 24vac return from transformer
24VAC RTN 24vac from transformer
FLAME SENSE flame sense terminal
TABLE 2
IGNITION CONTROL 97L48 J156 TERMINAL
DESIGNATIONS
PIN # FUNCTION
1 Ignitor
2Not Used
3Ignitor Neutral
4Combustion Air Inducer Line Voltage
5Not Used
6Combustion Air Inducer Neutral
TABLE 3
IGNITION CONTROL 97L48 J58 TERMINAL
DESIGNATIONS
PIN # FUNCTION
1Primary Limit In
2Gas Valve Common
3Roll Out Switch Out
4Gas Valve 24V
5Pressure Switch In
6Pressure Switch and Primary Limit Out
7Not Used
8Roll Out Switch In
9Ground
a−Electronic Ignition (See Figure 8)
On a call for heat the SureLight®control monitors the com-
bustion air inducer prove switch. The control will not begin
the heating cycle if the prove switch is closed (by−passed).
Once the proving switch is determined to be open, the com-
bustion 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 not
proven within 2−1/2 minutes, the control goes into Watch-
guard−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 ignition trial until
flame is sensed. If ignition is not proved during the 4−sec-
ond period, the control will try four more times with an inter
purge and warm−up time between trials of 35 seconds. Af-
ter a total of five trials for ignition (including the initial trial),
the control goes into Watchguard−Flame Failure mode. Af-
ter a 60−minute reset period, the control will begin the igni-
tion 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.

Page 10
b−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. 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.
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 7
The SureLight 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
97L48 − DIAG 1 Green
69M15 − DS1 Red
LED #2
97L48 − DIAG2 Green
69M15 − 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 Watchgurad.
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.
SLOW FLASH OFF Flame sensed without gas valve energized.
ON SLOW FLASH Rollout switch open. OR: Low voltage 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. See table 17 for flame signal Replace flame sense rod.
ALTERNATING
FAST FLASH
ALTERNATING
FAST FLASH
The following conditions are sensed during the ignitor warm−up period only:
1) Improper main ground;
2) Broken ignitor; OR: Open ignitor circuit;
3) Line voltage below 75 volts.
(If voltage lower than 75 volts prior to ignitor warm-up, control will signal waiting on call from
thermostat, and will not respond.
NOTE − Slow flash rate equals 1 Hz (one flash per second). Fast flash rate equals 3 Hz (three flashes per second).
FIGURE 8
SureLight Control Ignition Sequence Board
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉ
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
INDOOR BLOWER
ÉÉÉÉÉÉÉÉÉÉ
Blower On"
Delay
End of
Heat Demand Blower
Off
Time
*Blower on time will be 45 seconds after gas valve is energized. Blower off time will depend on OFF TIME" Setting.

Page 11
5. SureLight®Integrated Ignition Control
69M15 (A92)
The SureLight system consists of ignition control board (fi-
gue 9), ignitor (figure 11) and sensor (figure 12). The igni-
tion control and ignitor work in combination to ensure fur-
nace ignition and ignitor durability. The ignition control,
controls all major furnace operations. The ignition control
also features two LED lights (DS1 red and DS2 green) for
troubleshooting and two 120 volt accessory terminals
each rated at (1) one amp. A 24 volt accessory terminal
rated at 0.5 amps is also provided. Table 5 shows 24 volt
and 120 volt control terminal designations. Tables 6 and 7
show jack plug terminal designations. See table 4 for trou-
bleshooting diagnostic codes. Units equipped with the
SureLight system can be used with either electronic or
electro−mechanical thermostats without modification.
Each time power is applied to the furnace, the ignition con-
trol performs a selfcheck. The SureLight ignitor is made of
durable silicon−nitride. Ignitor longevity is also enhanced
by voltage ramping by the control board. The ignition con-
trol finds the lowest ignitor temperature which will suc-
cessfully light the burner, thus increasing the life of the ig-
nitor.
TABLE 5
IGNITION CONTROL 69M15 TERMINAL DESIGNATIONS
COOL Blower − Cooling Speed (120V)
HEAT Blower − Heating (120V)
PARK Unused blower lead not energized
FAN Continuous Low Blower Speed
EAC Accessory Terminal (120V)
XFMR Transformer (120V)
LINE Input (120V)
HUM Heat Only Accessory (120V)
5 Terminals 120 Volt Neutral
FS Flame Sensor
24V HUM Heat Only Accessory (24V)
TABLE 6
IGNITION CONTROL 69M15 TERMINAL DESIGNATIONS
PIN # FUNCTION
1Combustion Air Inducer Line Voltage
2Ignitor Voltage
3Combustion Air Inducer Neutral
4Ignitor Neutral
INTEGRATED IGNITION CONTROL 69M15
FIGURE 9

Page 12
c−Electronic Ignition (See Figure 8)
On a call for heat the SureLight control monitors the com-
bustion air inducer prove switch. The control will not begin
the heating cycle if the prove switch is closed (by−passed).
Once the proving switch is determined to be open, the com-
bustion 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 not
proven within 2−1/2 minutes, the control goes into Watch-
guard−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 trial until flame is sensed. If igni-
tion 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−minute 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.
d−Fan Time Control Heating
The heating 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
S1 dip switches located on the SureLight integrated con-
trol. 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. 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 al-
low for lower air temperature, shorter delay times allow for
higher air temperature). See table 8 for switch settings and
fan delay times..
e−Fan Time Control Cooling
The cooling fan on time is fixed at 2 seconds and cannot be
adjusted. Fan off time (time that the blower operates after
the cool demand has been satisfied) can be adjusted by
setting the S1 dip switches (switch 3) located on the Sur-
eLight integrated control. See table 8 for switch settings
and fan delay times.
TABLE 8
S1 DIP SWITCH SETTINGS
Heat Off Delay
Switch 1 Switch 2 SECONDS
OFF OFF 60
OFF ON 90
ON OFF 120
ON ON 180
Cool Off Delay
Switch 3 SECONDS
OFF 2
ON 45

Page 13
Blower Control Module (Figure 10)
G50UHi units are equipped with a blower control module
which offers a variety of indoor blower speeds for selection.
The module is wired between the SureLight ignition control
board and the indoor blower motor. The module alters the
frequency and voltage of the power supply to the blower to
control blower speed. The module provides consistent
CFM over a wider range of operating static pressures.
The module also features a dehumidification option. This
option requires the use of a thermostat which includes a hu-
midity sensor, as well as a relay, which must both be or-
dered separately. When this optional feature is used, the
blower control module shifts the indoor blower motor to a
lower speed (determined by the selector jumper) when the
indoor thermostat indicates a dehumidification require-
ment.
The module includes a ramping profile selector, which of-
fers passive humidity control during cooling operation. This
feature does not require the use of a specific thermostat or
an additional relay. There are three available ramping pro-
files. When one of the ramping profiles is used, the indoor
blower is initially engaged at a lower speed to provide addi-
tional humidity control. After the selected time period
(7−1/2, 10, or 15 minutes), the blower motor shifts to the
regularly selected cooling speed.
The module/bracket assembly is located on the blower
scroll just below the SureLight control board. Blower
speeds are adjusted by altering the position of blower
speed selector jumpers.
Blower Control Module Settings
DANGER
Disconnect power from unit and
wait at least 30 seconds to allow
capacitors to discharge before re-
moving blower control module
cover. Failure to wait may cause
personal injury or death.
Remove the cover panel from the module to access the se-
lector jumpers. There are five selector pins in each column.
These pins, when jumpered, correspond with four selec-
tion options for each function. The speed (or ramp) selec-
tion is listed in the space between the two pins. There are
eight blower speeds and four ramping options available for
selection on the control module. Refer to table 9 and figure
10. The blower speed settings and the corresponding
CFMs are given in the BLOWER DATA section.
The ramping options provide a means of controlling humid-
ity during cooling operation without the use of a humidity
sensor or additional relay.
Ramping Option A (Factory Selection)
DMotor runs at 82% for approximately 7−1/2 minutes.
DIf demand has not been satisfied after 7−1/2 minutes,
motor runs at 100% until demand is satisfied.
DOnce demand is met, motor ramps down to off.
OFF
OFF 82%CFM 100% CFM
COOLING DEMAND
7−1/2 MIN
Ramping Option B
DMotor runs at 75% for approximately 10 minutes.
DIf demand has not been satisfied after 10 minutes, mo-
tor runs at 100% until demand is satisfied.
DOnce demand is met, motor ramps down to off.
OFF
OFF 75%CFM 100% CFM
COOLING DEMAND
10 MIN
Ramping Option C
DMotor runs at 75% for approximately 15 minutes.
DIf demand has not been satisfied after 15 minutes, the
motor runs at 100% until demand is satisfied.
DOnce demand is met, motor ramps down to off.
OFF
OFF 75%CFM 100% CFM
COOLING DEMAND
15 MIN
G50UHi BLOWER CONTROL MODULE
6−PIN CONNECTOR
TO SURELIGHT
CONTROL
SELECTOR PINS
WITH JUMPERS
(Options detailed at right)
3−PIN MOTOR
CONNECTOR
FIGURE
COOL HEAT FAN DEHUM. RAMP
1
1
3
4
2
3
4
5
2
5
6
7
3
4
5
6
OFF
A
B
C
4−Ton and 5−Ton Blowers
COOL HEAT FAN DEHUM. RAMP
1
2
3
4
3−Ton Blower
1
1
3
4
2
5
6
7
3
4
5
6
OFF
A
B
C

Page 14
TABLE 9
Blower Mode Available Options Factory Default
Cool Speeds 1, 3, 4 Speed 1
Heat (3−ton) Speeds 1, 2, 3, 4 Speed 3
Heat (4 & 5−ton) Speeds 2, 3, 4, 5 Speed 4
Fan Speeds 2, 5, 6, 7 Speed 7
Dehumidification Speeds 3, 4, 5, 6 Speed 3
Ramp OFF, A, B, C Ramp A
6. Ignitor
The SureLight®ignitor is made of durable silicon nitride. Ig-
nitor longevity is enhanced by controlling voltage to the ig-
nitor. 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 so ignitor must be ohmed. Ohm value should
be 10.9 to 19.7. See figure 11 for ignitor location.
FIGURE 11

Page 15
A proving switch connected to the combustion air inducer ori-
fice plate is used to prove inducer operation. The combustion
air inducer orifice will be different for each model. See table
10 for orifice sizes. The switch monitors air pressure in the in-
ducer housing. During normal operation, the pressure in the
housing is negative. If pressure becomes less negative (sig-
nifying an obstruction) the proving switch opens. When the
proving switch opens, the furnace control (A92) immediately
closes the gas valve to prevent burner operation.
TABLE 10
G50UHi Unit C.A.I. Orifice Size
−070 1 7/16"
−090 1 11/16"
−110 2 5/32"
−135 2 3/8"
Horizontal Applications
The G50UHi furnace can be installed in horizontal applica-
tions.
The combustion air inducer may be rotated clockwise or
counterclockwise by 90° to allow for vertical vent discharge
in a horizontal application. Remove the four mounting
screws, rotate the assembly (assembly consists of orifice
plate, proving switch, gasket and combustion air inducer),
then reinstall the mounting screws. See figure 14. Use the
provided wire tie to bundle the pressure switch wires with
the inducer motor power leads. Route the wires away
from moving parts and the heat of the inducer motor to
prevent damage to the wires. Use sheet metal shears to
remove the cut out from the side of the cabinet. See figure
15. Use the two provided sheet metal screws to install the
cut out on the top cap to cover the original flue outlet open-
ing.
Combustion Air Inducer
(Upflow Position)
Mounting Screws
MOUNTING SCREWS
90° 90°
(Remove)
(Remove) Power Leads
Flue Transition
(Do not remove)
FIGURE 14
Flue Outlet Hole
(Reattach
Cutout Here) Supply Air
Opening
Top View of Furnace
Top Cap
Cut out
Optional
Flue Outlet
Optional Flue Outlet
(Horizontal Installation)
FIGURE 15
10. Flame Rollout Switches (S47)
Flame rollout switch is a high temperature limit located on
top of the burner box (135 and 155 Btuh units− rollout
switches are located on the inner sides of burner box).
Each furnace is equipped with two identical switches. One
switch is located over the far left burner and the other
switch is located over the far right burner. The limit is a N.C.
SPST manual-reset limit connected in series with the igni-
tion control A92. When S47 senses rollout, the ignition con-
trol immediately stops ignition and closes the gas valve. If
unit is running and flame rollout is detected, the gas valve
will close and ignition control will be disabled. Rollout can
be caused by a blocked heat exchanger, flue or lack of
combustion air. The switch is factory set and cannot be ad-
justed. See table 11. The switch can be manually reset. To
manually reset a tripped switch, push the reset button located
on the control.
TABLE 11
BTUH INPUT Rollout Switch Setpoint
−070
−090 250° F
−110
−135 200° F

Page 16
11. Primary Limit Control (S10)
The primary limit (S10) on G50UHi units is located in the heat-
ing vestibule panel. When excess heat is sensed in the heat
exchanger, the limit will open. If the limit is open, the furnace
control energizes the supply air blower and closes the gas
valve. The limit automatically resets when unit temperature re-
turns to normal. The switch must reset within three minutes or
SureLight board will go into Watch guard for one hour. The
switch is factory set and cannot be adjusted. The switch may
have a different setpoint for each unit model number. If limit
switch must be replaced, see Lennox Repair Parts hand-
book.
12. Secondary Limit Controls (S21)
The secondary limit (S21) on G50UHi units is located in the
blower compartment in the back side of the blower housing.
See figure 13. Table 12 and the blower speed chart on the wir-
ing diagram show secondary limit quantities per unit. When
excess heat is sensed in the blower compartment, the limit will
open. If the limit is open, the furnace control energizes the sup-
ply air blower and closes the gas valve. The limit automatically
resets when unit temperature returns to normal. G50UHi−1
through −6 units use a surface type limit, factory set to open at
125°F. G50UHi −7 and later units use an air stream limit fac-
tory set to open at 135°. The secondary limit cannot be ad-
justed.
TABLE 12
G50UHi
UNIT Quantity LeftSide Right Side
36A−070 2Yes Yes
36B−090 1No Yes
48B−090 2Yes Yes
60C−110 1No Yes
60D−135 2Yes Yes
13. Gas Valve (GV1) Figures 16, 17 & 18
The G50UHi uses a gas valve manufactured by Honeywell
or White Rodgers. The valve is internally redundant to as-
sure safety shut−off. If the gas valve must be replaced, the
same type valve must be used.
24VAC terminals and gas control knob or switch are located
on the valve. All terminals on the gas valve are connected to
wires from the electronic ignition control. 24V applied to the ter-
minals energizes the valve.
Inlet and outlet pressure taps are located on the valve. A regu-
lator adjustment screw is located on the valve.
LPG changeover kits are available from Lennox. Kit s include
burner orifices and a gas valve regulator conversion kit.
WHITE RODGERS 36E SERIES GAS VALVE
GAS VALVE SHOWN IN OFF POSITION
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
MANIFOLD
PRESSURE
OUTLET

Page 17
Set points vary depending on unit size. See table 13. The
pressure sensed by the switch is negative relative to atmo-
spheric pressure. If the flue becomes obstructed during op-
eration, the switch senses a loss of negative pressure
(pressure becomes more equal with atmospheric pres-
sure) and opens the circuit to the furnace control and gas
valve. A bleed port on the switch allows relatively dry air in
the vestibule to purge switch tubing, to prevent condensate
build up.
The switch is factory set and is not field adjustable. It is a
safety shut-down control in the furnace and must not be by−
passed for any reason. If switch is closed or by−passed, the
control will not initiate ignition at start up.
TABLE 13
G50UHi Unit Set
Point
High Altitude
Set Point
4501’ − 7500’
High Altitude
Set Point
7500’ − 10,000’
−070 0.47" 0.36" 0.36"
−090 0.51" 0.47" 0.43"
−110 0.58" 0.47" 0.43"
−135 0.51" 0.47" 0.43"
II−PLACEMENT AND INSTALLATION
Make sure unit is installed in accordance with installation
instructions and applicable codes.
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
WARNING
Shock and burn hazard. G50UHi units are equipped
with a hot surface ignition system. Do not attempt to
light manually.
1 − STOP! Read the safety information at the beginning of
this section.
2 − Set thermostat to lowest setting.
3 − Turn off all electrical power to appliance.
4 − This appliance is equipped with an ignition device
which automatically lights the burners. Do not try to
light the burners by hand.
5 − Remove top access panel.
6 − White Rodgers Gas Valve −− Switch lever to OFF.
See figure 16. Honeywell Gas Valve −− Turn knob on
gas valve clockwise to OFF. Do not force. See
figure 18.
7 − Wait five (5) minutes to clear out any gas. If you then
smell gas, STOP! Immediately call your gas supplier from
a neighbor’s phone. Follow the gas supplier’s instruc-
tions. If you do not smell gas go to next step.
8 − White Rodgers Gas Valve −− Switch gas valve lever to
ON.
Honeywell Gas Valve −− Turn knob on gas valve coun-
terclockwise to ON. Do not force.
9 − Replace access panel.
10− Turn on all electrical power to unit.
11− Set thermostat to desired setting.
12− If the appliance will not operate, follow the instructions
To Turn Off Gas To Unit" and call your service techni-
cian or gas supplier.
Turning Off Gas To Unit
1 − Set thermostat to lowest setting.
2 − Turn off all electrical power to unit if service is to be per-
formed.
3 − Remove access panel.
4 − Switch lever on White Rodgers gas valve to OFF; turn
knob on Honeywell valve clockwise to OFF. Do not
force.
5 − Replace access panel.
C−Safety or Emergency Shutdown
Turn off unit power. Close manual and main gas valves.
D−Extended Period Shutdown
Turn off thermostat or set to UNOCCUPIED" mode. Close
all gas valves (both internal and external to unit) to guaran-
tee no gas leak into combustion chamber. Turn off power to
unit. All access panels and covers must be in place and se-
cured.
IV−HEATING SYSTEM SERVICE CHECKS
A−C.S.A. Certification
All units are C.S.A. (formally A.G.A. and C.G.A. combined)
design certified without modifications. Refer to the G50UHi
Installation Instruction.
B−Gas Piping
CAUTION
If a flexible gas connector is required or allowed by
the authority that has jurisdiction, black iron pipe
shall be installed at the gas valve and extend outside
the furnace cabinet.
WARNING
Do not exceed 600 in−lbs (50 ft−lbs) torque when
attaching the gas piping to the gas valve.
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.

Page 18
C−Testing Gas Piping
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.
When pressure testing gas lines, the gas valve must be dis-
connected and isolated. Gas valves can be damaged if
subjected to more than 0.5psig (14" W.C.). See figure 19. If
the pressure is equal to or less than 0.5psig (14"W.C.), use
the manual shut−off valve before pressure testing to isolate
furnace from gas supply.
FIGURE 19
MANUAL MAIN SHUT−OFF VALVE
WILL NOT HOLD TEST PRESSURE
IN EXCESS OF 0.5 PSIG (14"W.C.)
GAS VALVE
CAP
GAS PIPING TEST PROCEDURE
FIELD PROVIDED
LINE PRESSURE TAP
When checking piping connections for gas leaks, use pre-
ferred means. Kitchen detergents can cause harmful corro-
sion 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 19. Check gas
line pressure with unit firing at maximum rate. Low pres-
sure may result in erratic operation or underfire. High pres-
sure can result in permanent damage to gas valve or over-
fire. See table 14 for operating pressure at unit gas connec-
tion (line).
On multiple unit installations, each unit should be checked
separately, with and without units operating. Supply pres-
sure 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 gauge to outlet pres-
sure tap located on unit gas valve (GV1). Checks of man-
ifold pressure are made as verification of proper regulator ad-
justment. Manifold pressure for the G50UHi can be mea-
sured at any time the gas valve is open and is supplying gas
to the unit. See table 14 for normal operating manifold pres-
sure. See page 2 for high altitude applications.
TABLE 14
All G50UHi Units Natural LP
Line Pressure WC" 4.5 − 10.5 11.0 − 13.0
Manifold Pressure WC" 3.5 10.0
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.
The gas valve is factory set and should not require adjust-
ment. All gas valves are factory regulated. See specifica-
tions section of this manual for High Altitude manifold pres-
sure settings.
Manifold Adjustment Procedure:
1 − Connect a test gauge to outlet pressure tap on gas
valve. See figures 16, 17 and 18. 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, record
manifold pressure.
NOTE−Shut unit off and remove manometer as soon as
an accurate reading has been obtained. Take care to re-
place pressure tap plug.
F− Proper Gas Flow (Approximate)
Furnace should operate at least 5 minutes before check-
ing gas flow. Determine time in seconds for two revolu-
tions of gas through the meter. (Two revolutions assures a
more accurate time.) Divide by two and compare to time
in table 15 below. If manifold pressure matches table 14
and rate is incorrect, check gas orifices for proper size and
restriction.
NOTE− To obtain accurate reading, shut off all other gas
appliances connected to meter.

FIGURE 20
TRANSDUCER
(PART #78H5401)
Page 19
TABLE 15
GAS METER CLOCKING CHART
Seconds for One Revolution
G50UH Natural LP
G50UH
Unit 1 cu ft
Dial
2 cu ft
Dial
1 cu ft
Dial
2 cu ft
DIAL
−70 55 110 136 272
−90 41 82 102 204
−110 33 66 82 164
−135 27 54 68 136
Natural−1000 btu/cu ft LP−2500 btu/cu ft
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.
G− Proper Combustion
Furnace should operate minimum 15 minutes with correct
manifold pressure and gas flow rate before checking com-
bustion. See sections E− and F−. Take combustion sample
beyond the flue outlet and compare to table 16. The maxi-
mum carbon monoxide reading should not exceed 100
ppm.
TABLE 16
Unit CO2%For Nat CO2% For L.P.
G50UHi−36A−070 5.8 − 7.8 6.8 − 8.8
G50UHi−36B−090 6.2 − 8.2 6.7 − 8.7
G50UHi−48B−090 6.2 − 8.2 6.7 − 8.7
G50UHi−60C−110 5.9 − 7.9 7.5 − 9.5
G50UHi−60D−135 6.5 − 8.5 7.5 − 9.5
H−Flame Signal
A microamp DC meter is needed to check the flame signal
on the ignition control.
Flame (microamp) signal is an electrical current which passes
from the furnace control through the sensor during unit opera-
tion. Current passes from the sensor through the flame to
ground to complete a safety circuit.
TABLE 17
Flame Signal in Microamps
Ignition Control Normal Low Drop Out
97L48 0.61 0.21 − 0.60 0.20
69M15 0.31 0.25 − 0.30 0.24
To Measure Flame Signal − Ignition Control:
A transducer (Part
#78H5401 available from
Lennox Repair Parts) is
required to measure flame
signal if meter used will not
read a low micro amp sig-
nal. Seefigure20. The
transducer converts mi-
croamps to volts on a 1:1 conversion. See table 17 for flame
signal. A digital readout meter must be used. The transduc-
er plugs into most meters. See figure 21 for proper use of
transducer.
1 − Set the volt meter to the DC voltage scale. Insert
transducer into the VDC and common inputs. Ob-
serve correct polarities. Failure to do so results in
negative (−) values.
2 − Turn off supply voltage to control.
3 − Disconnect ignition control flame sensor wire from the
flame sensor.
4 − Connect (−) lead of the transducer to flame sensor.
5 − Connect (+) lead of transducer to the ignition control sen-
sor wire.
6 − Turn supply voltage on and close thermostat contacts to
cycle system.
7 − When main burners are in operation for two minutes, take
reading. Remember 1 DC volt = 1 DC microamp.
SET DIAL TO MEASURE VDC
(+)
(−) TO
FLAME
SENSOR
NOTE−MUST USE DIGITAL METER
RED COLLAR
INDICATES
POSITIVE
LEAD
(+) TO
IGNITION
CONTROL
SENSOR
WIRE
FIGURE 21
(−)

STATIC PRESSURE TEST
FIGURE 22
Page 20
V−TYPICAL OPERATING CHARACTERISTICS
A−Blower Operation and Adjustment
1 − Blower operation is dependent on thermostat control
system.
2 − Generally, blower operation is set at thermostat sub-
base fan switch. With fan switch in ON position, blower
operates continuously. With fan switch in AUTO position,
blower cycles with demand or runs continuously while
heating or cooling circuit cycles.
3 − Depending on the type of indoor thermostat, blower
and entire unit will be off when the system switch is in
OFF position.
B−Temperature Rise
Temperature rise for G50UHi 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 TEMP. RISE °F"
listed on 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 hori-
zontal run of the plenum where it will not pick up radiant
heat from the heat exchanger.
2 − Set thermostat to highest setting.
3 − After plenum thermometers have reached their high-
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, in-
crease blower speed to reduce temperature.
C−External Static Pressure
1 − Tap locations shown in figure 22 .
2 − Punch a 1/4" diameter hole
in supply and return air ple-
nums. Insert manometer
hose flush with inside edge
of hole or insulation. Seal
around the hose with perma-
gum. Connect the zero end
of the manometer to the dis-
charge (supply) side of the system. On ducted sys-
tems, connect the other end of manometer to the return
duct as above. For systems with non−ducted returns,
leave the other end of the manometer open to the at-
mosphere.
3 − With only the blower motor running and the evaporator
coil dry, observe the manometer reading. Adjust blow-
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.
VI−MAINTENANCE
WARNING
Disconnect power before servicing unit.
CAUTION
Label all wires prior to disconnection when servicing
controls. Wiring errors can cause improper and dan-
gerous operation. Verify proper operation after ser-
vicing.
At the beginning of each heating season, a qualified techni-
cian should check the system as follows:
Blower
Check the blower wheel for debris and clean if necessary.
The blower motors are prelubricated for extended bearing
life. No further lubrication is needed.
WARNING
The blower access panel must be securely in place
when the blower and burners are operating. Gas
fumes, which could contain carbon monoxide, can
be drawn into living space resulting in personal inju-
ry or death.
Filters
All G50UHi filters are installed external to the unit. Filters
should be inspected monthly. Clean or replace the filters
when necessary to ensure that the furnace operates prop-
erly. Replacement filters must be rated for high velocity air-
flow. Table 18 lists recommended filter sizes.
TABLE 18
Furnace Filter Size
Furnace
Cabinet Size Side Return Bottom Return
14−1/2" 16 X 25 X 1 (1) 14 X 25 X 1 (1)
17−1/2" 16 X 25 X 1 (1) 16 X 25 X 1 (1)
21" 16 X 25 X 1 (1) 20 X 25 X 1 (1)
24−1/2" 16 X 25 X 1 (2) 24 X 25 X 1 (1)
Flue And Chimney
Check the flue pipe, chimney and all connections for tight-
ness and to make sure there is no blockage.
Electrical
1 − Check all wiring for loose connections.
2 − Check for the correct voltage at the furnace (furnace
operating).
3 − Check amp−draw on the blower motor.
Motor Nameplate__________Actual__________