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.