Lennox G40DF?24A?045 Installation and operation manual

Page 1 ©2001 Lennox Industries Inc.
G40DF(X)
Service Literature
Corp. 0113−L6
Revised 09−2006
G40DF(X) series units are mid−efficiency gas furnaces
used for downflow applications only, manufactured with
Lennox Duralok Plus heat exchangers formed of alumi-
nized steel. G40DF(X) units are available in heating capac-
ities of 44,000 to 135,000 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. G40DF(X) model
units are equipped with a hot surface ignition surface. The
G40DF(X) unit meets the California Nitrogen Oxides (NOx)
Standards and California Seasonal Efficiency requirements.
All units use a redundant gas valve to assure safety shut−off
as required by 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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Blower Data 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
High Altitude 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Parts Identification 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I Unit Components 9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
II Installation 18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
III Start Up 18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IV Heating System Service Checks 18. . . . . . . . . . . . . .
V Typical Operating Characteristics 20. . . . . . . . . . . . . .
VI Maintenance 21. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VII Wiring and Sequence of Operation 23. . . . . . . . . . .
VIII SureLight Troubleshooting Guide 33. . . . . . . . . . . .
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
Heating
Pf
ModelNo. G40DF
−24A−045
G40DF
−36A−045
G40DF
−36A−070
G40DF
−36B−090
G40DF
−48B−070
eat g
Performance Low NOxModel No. −24A−045X − − − −36A−070X − − − − − −
Input− Btuh 44,000 44,000 66,000 88,000 66,000
Output− Btuh 36,000 35,000 53,000 71,000 53,000
1AFUE 80.0% 80.0% 80.0% 80.0% 80.0%
Highstatic(CSA)− in.w.g. .50 .50 .50 .50 .50
Temperature rise range − _F 20 − 50 20 − 50 35 − 65 45 − 75 25 − 55
Connections Flue connection − in. (round) 44444
GaspipesizeIPS− in. 1/2 1/2 1/2 1/2 1/2
Indoor
Blower
Wheelnominaldiameter xwidth −in. 10 x 7 10 x 8 10 x 8 10 x 8 10 x 10
Bl
ower
Motoroutput − hp 1/5 1/3 1/3 1/3 1/2
Tons ofadd-oncooling 1.5 − 2 2 − 3 2 − 3 2 − 3 3 − 4
ShippingData lbs. − 1 package 121 126 132 146 139
Electricalcharacteristics 120 volts − 60 hertz − 1 phase (less than 12 amps)
SPECIFICATIONS
Gas
Heating
Pf
ModelNo. G40DF
−48C−090
G40DF
−48C−110
G40DF
−60C−110
G40DF
−60D−135
eat g
Performance Low NOxModel No. −48C−090X − − − −60C−110X − − −
Input− Btuh 88,000 110,000 110,000 132,000
Output− Btuh 71,000 89,000 90,000 107,000
1AFUE 80.0% 80.0% 80.0% 80.0%
Highstatic(CSA)− in.w.g. .50 .50 .50 .50
Temperature rise range − _F 45 − 75 45 − 75 35 − 65 40 − 70
Connections Flue connection − in. (round) 4 4 4 4
GaspipesizeIPS− in. 1/2 1/2 1/2 1/2
Indoor
Blower
Wheelnominaldiameter xwidth −in. 10 x 10 10 x 10 11−1/2 x 10 11−1/2 x 10
Bl
ower
Motoroutput − hp 1/2 1/2 1* 1*
Tons ofadd-oncooling 3 − 4 2.5 − 4 4 − 5 4 − 5
ShippingData lbs. − 1 package 153 169 172 195
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.
1Annual Fuel Utilization Efficiency based on DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherized furnaces.
*Some units may be equipped with 3/4 hp motors.

Page 3
OPTIONAL ACCESSORIES − MUST BE ORDERED EXTRA
A" Width Models B" Width Models C" Width Models D" Width Models
CABINET ACCESSORIES
Down−Flow Additive Base 11M59 11M60 11M61 11M62
CONTROLS
Twinning Kit 15L38 15L38 15L38 15L38
1Cleanable polyurethane frame type filter.
HIGH ALTITUDE
Input −1
through
1High Altitude
Orifice Kit
High Altitude Pressure
Switch Kit LPG/Propane Kit
through
−14
g
Orifice Kit
Natural Gas Only 4501−7500 ft.
(1373 − 2286m)
7501−10,000 ft.
(2287 − 3048m)
0−7500 ft.
(0 − 2286m)
7501−10,000 ft.
(2287 − 3048m)
−044
−070 59M16 no change no change 45L60 47M81
−090 59M16 15M22 56L32 45L60 47M81
−110 59M16 15M22 56L32 45L60 47M81
−135 59M16 49L90 15M22 45L60 47M81
In
p
ut −15 1High Altitude
Orifice Kit
High Altitude Pressure
Switch Kit LPG/Propane Kit
Input
−15
and later
g
Orifice Kit
Natural Gas Only 4501−7500 ft.
(1373 − 2286m)
7501−10,000 ft.
(2287 − 3048m)
0−7500 ft.
(0 − 2286m)
7501−10,000 ft.
(2287 − 3048m)
−045
−070 59M17 no change no change 25W20 25W21
−090 59M17 15M22 56L32 45L60 25W21
−110 59M17 15M22 56L32 25W20 25W21
−135 59M17 49L90 15M22 25W20 25W21
1Required for proper operation at altitudes from 7501 to 10,000 ft.
NOTE − G40DF(X) units do NOT require a manifold change due to elevation. Manifold pressureremains the same at all
elevations.
BLOWER DATA
G40DF−24A−045 PERFORMANCE
External Static Air Volume / Watts at Different Blower Speeds
External
Static
Pressure High Medium Low
in. w.g. Pa cfm L/s Watts cfm L/s Watts cfm L/s Watts
0.00 0 1202 565 417 1058 500 367 828 390 278
0.05 12 1185 560 410 1041 490 360 819 385 274
0.10 25 1167 550 402 1024 482 353 809 380 270
0.15 37 1147 540 396 1008 475 346 793 375 265
0.20 50 1127 530 390 991 470 338 776 365 260
0.25 62 1104 520 382 979 460 335 764 360 257
0.30 75 1081 510 374 966 455 331 752 355 254
0.40 100 1018 480 357 922 435 319 712 335 244
0.50 125 960 455 342 873 410 306 651 305 234
0.60 150 901 425 330 811 385 290 618 290 231
0.70 175 815 385 313 691 325 272 564 265 221
0.80 200 685 325 289 619 290 259 465 220 203
0.90 225 558 265 271 510 240 238 395 185 190
NOTE − 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.

Page 4
BLOWER DATA Cont.
G40DF−36A−070 PERFORMANCE
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 1475 695 616 1343 635 554 1151 545 495 989 465 415
0.05 12 1449 685 606 1321 625 543 1139 540 481 983 465 407
0.10 25 1423 670 595 1298 615 532 1127 530 466 976 460 398
0.15 37 1397 660 585 1276 600 521 1115 525 452 970 460 390
0.20 50 1371 645 574 1253 590 510 1103 520 437 963 455 381
0.25 62 1345 635 563 1228 580 494 1090 515 428 953 450 371
0.30 75 1318 620 552 1203 570 478 1077 510 418 943 445 360
0.40 100 1249 590 528 1151 545 455 1039 490 395 918 435 346
0.50 125 1200 565 508 1094 515 432 998 470 374 882 415 331
0.60 150 1112 525 475 1033 490 409 951 450 354 831 390 313
0.70 175 1032 485 455 968 455 390 856 405 338 722 340 280
0.80 200 959 455 434 876 415 359 737 350 299 666 315 266
0.90 225 770 365 389 715 335 321 667 315 278 591 280 244
NOTE − 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.
G40DF−36B−090 PERFORMANCE
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 1598 755 608 1408 665 526 1166 550 436 963 455 355
0.05 12 1579 745 599 1398 660 518 1164 550 428 966 455 351
0.10 25 1559 735 589 1388 655 509 1161 550 420 968 455 346
0.15 37 1528 720 573 1369 645 497 1156 545 413 966 455 341
0.20 50 1497 705 556 1350 635 485 1150 545 406 964 455 335
0.25 62 1465 690 544 1326 625 473 1137 535 398 955 450 329
0.30 75 1432 675 532 1301 615 460 1124 530 389 945 445 323
0.40 100 1370 645 509 1248 590 438 1093 515 373 933 440 313
0.50 125 1294 610 482 1198 565 420 1055 500 355 902 425 302
0.60 150 1213 575 456 1141 540 397 1012 480 343 862 405 285
0.70 175 1139 540 437 1054 495 371 917 435 313 802 380 272
0.80 200 1002 475 401 948 445 342 850 400 295 728 345 251
0.90 225 901 425 374 822 390 313 740 350 272 − − − − − − − − −
NOTE − 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.

Page 5
BLOWER DATA Cont.
G40DF−36C−110 PERFORMANCE
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 1660 785 668 1425 675 589 1205 570 489 1015 480 409
0.05 12 1635 770 652 1415 670 575 1205 570 480 1010 475 405
0.10 25 1610 760 636 1405 665 560 1205 570 471 1010 475 402
0.15 37 1575 745 617 1395 660 544 1200 565 460 1005 475 395
0.20 50 1535 725 597 1380 650 524 1200 565 449 1005 475 387
0.25 62 1490 705 576 1350 635 506 1190 560 436 1000 470 380
0.30 75 1450 685 556 1320 625 488 1175 555 422 1000 470 372
0.40 100 1350 635 516 1250 590 456 1125 530 400 970 460 347
0.50 125 1230 580 472 1150 545 416 1045 495 365 910 430 319
0.60 150 1110 525 438 1025 485 374 950 450 329 820 385 284
0.70 175 950 450 396 870 410 329 800 380 286 695 330 251
0.80 200 800 380 362 715 390 294 675 320 245 − − − − − − − − −
0.90 225 685 325 300 625 295 237 560 265 208 − − − − − − − − −
NOTE − 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.
G40DF−48C−090 PERFORMANCE
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 2039 960 749 1852 875 657 1595 755 562 1325 625 466
0.05 12 1998 945 727 1826 860 638 1576 745 547 1338 632 460
0.10 25 1956 925 704 1800 850 619 1556 735 532 1351 640 453
0.15 37 1921 905 692 1770 835 602 1541 725 518 1340 630 441
0.20 50 1885 890 679 1739 820 585 1526 720 503 1329 625 428
0.25 62 1844 870 662 1701 805 568 1502 710 488 1301 615 414
0.30 75 1802 850 645 1663 785 551 1477 695 473 1272 600 399
0.40 100 1693 800 606 1583 745 517 1415 670 448 1226 580 378
0.50 125 1600 755 570 1491 705 485 1334 630 414 1170 550 360
0.60 150 1494 705 540 1406 665 457 1248 590 389 1110 525 337
0.70 175 1378 650 509 1300 615 426 1166 550 367 1026 485 316
0.80 200 1248 590 478 1161 550 390 1027 485 331 − − − − − − − − −
0.90 225 1097 520 439 1028 485 360 925 435 307 − − − − − − − − −
NOTE − 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.
G40DF−48C−110 PERFORMANCE
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 2034 960 846 1790 845 712 1508 710 595 1226 580 477
0.05 12 2001 945 825 1761 830 694 1493 705 581 1224 580 470
0.10 25 1968 930 803 1731 815 675 1477 695 567 1222 575 463
0.15 37 1924 910 781 1708 805 657 1470 695 555 1219 575 455
0.20 50 1879 885 758 1685 795 638 1463 690 542 1216 575 447
0.25 62 1837 865 736 1654 780 618 1442 680 528 1201 565 437
0.30 75 1794 845 714 1623 765 597 1420 670 514 1186 560 427
0.40 100 1681 795 669 1548 730 564 1361 640 483 1134 535 400
0.50 125 1622 765 630 1445 680 524 1280 605 447 1065 505 371
0.60 150 1447 685 592 1312 620 479 1165 550 404 1000 470 343
0.70 175 1289 610 545 1178 555 434 1056 500 369 907 430 319
0.80 200 1157 545 502 1067 505 406 956 450 348 816 385 296
0.90 225 1012 480 472 931 440 372 840 395 320 690 325 265
NOTE − 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.

Page 6
BLOWER DATA Cont.
5 ton units with 3/4 hp
G40DF−60C−110 PERFORMANCE
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
.00 0 2450 1155 1170 2355 1110 1005 2145 1015 840 1845 870 705
.05 10 2430 1150 1165 2340 1105 995 2130 1005 835 1840 870 695
.10 25 2380 1120 1145 2315 1090 985 2105 995 825 1830 865 690
.15 35 2350 1110 1135 2260 1065 965 2085 985 815 1815 855 680
.20 50 2300 1085 1115 2235 1055 955 2060 975 805 1805 850 675
.25 60 2270 1070 1105 2205 1040 945 2015 950 785 1780 840 665
.30 75 2245 1060 1100 2150 1015 925 1995 940 775 1770 835 655
.40 100 2135 1010 1060 2070 975 895 1925 910 750 1730 815 640
.50 125 2055 970 1035 1990 940 870 1855 875 725 1695 800 625
.60 150 1975 930 1010 1910 900 845 1785 845 705 1650 775 605
.70 175 1870 880 980 1830 865 820 1695 800 680 1575 745 585
.80 200 1760 830 950 1720 815 795 1605 755 655 1505 710 570
.90 225 1625 765 915 1560 735 755 1515 715 640 1435 675 555
G40DF−60D−135 PERFORMANCE
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 2845 1345 1143 2692 1270 961 2451 1155 818 2054 970 686
0.05 12 2774 1310 1128 2628 1240 948 2354 1110 809 2022 955 680
0.10 25 2702 1275 1112 2564 1210 935 2256 1065 799 1989 940 674
0.15 37 2629 1240 1095 2494 1175 918 2203 1040 784 1933 910 666
0.20 50 2556 1205 1077 2424 1145 901 2150 1015 769 1877 885 657
0.25 62 2471 1165 1061 2309 1090 890 2089 985 759 1835 865 649
0.30 75 2385 1125 1045 2194 1035 878 2028 955 749 1792 845 640
0.40 100 2184 1030 1022 2066 975 851 1900 895 727 1697 800 626
0.50 125 2019 955 990 1917 905 830 1779 840 707 1584 750 602
0.60 150 1865 880 957 1760 830 796 1630 770 676 1491 705 583
0.70 175 1697 800 927 1592 750 768 1475 695 656 1364 645 557
0.80 200 1513 715 897 1485 700 740 1378 650 627 1266 600 538
0.90 225 1385 655 863 1305 615 712 1206 570 598 1120 530 516
NOTE − 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.

Page 7
BLOWER DATA Cont.
5 ton units with 1 hp
G40DF−60C−110 PERFORMANCE
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
.00 0 2475 1170 1276 2280 1075 987 1995 940 845 1690 795 698
.10 25 2390 1125 1248 2235 1055 955 1990 940 829 1675 790 690
.20 50 2330 1100 1223 2180 1030 945 1975 930 809 1665 785 675
.30 75 2245 1060 1192 2125 1000 911 1940 915 786 1660 785 657
.40 100 2175 1025 1187 2050 965 880 1895 895 757 1650 780 636
.50 125 2085 985 1145 1970 930 849 1835 870 734 1625 765 619
.60 150 2020 955 1129 1880 885 815 1750 825 695 1580 745 599
.70 175 1920 905 1094 1775 835 785 1660 785 669 1525 720 579
.80 200 1785 840 1052 1685 795 762 1585 745 645 1440 680 556
.90 225 1670 790 1020 1600 755 741 1520 715 633 1370 645 538
G40DF−60D−135 PERFORMANCE
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
.00 0 2660 1255 1379 2325 1095 1059 1960 925 864 1655 780 684
.10 25 2560 1210 1353 2310 1090 1030 1945 915 840 1640 775 667
.20 50 2490 1175 1325 2280 1075 1000 1940 915 824 1630 770 661
.30 75 2415 1140 1293 2225 1050 972 1930 910 801 1625 765 649
.40 100 2345 1105 1264 2170 1025 941 1910 900 779 1620 760 638
.50 125 2265 1070 1235 2115 1000 918 1870 880 754 1615 760 624
.60 150 2165 1020 1199 2020 955 880 1830 865 733 1585 745 604
.70 175 2050 965 1160 1940 915 854 1755 830 705 1570 740 604
.80 200 1955 920 1112 1865 880 828 1680 790 683 1515 715 584
.90 225 1865 880 1096 1760 830 797 1605 755 656 1465 690 567
NOTE − 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.
FILTER AIR RESISTANCE
cfm L/s in. w.g. Pa cfm L/s in. w.g. Pa
0 0 0.00 0 1400 660 0.15 35
200 95 0.01 0 1600 755 0.19 45
400 190 0.03 5 1800 850 0.23 55
600 285 0.04 10 2000 945 0.27 65
800 380 0.06 15 2200 1040 0.33 80
1000 470 0.09 20 2400 1130 0.38 95
1200 565 0.12 30 2600 1225 0.44 110
Data is for 1 inch (25 mm) cleanable filter (field provided).

Page 8
G40DF(X) PARTS ARRANGEMENT
FIGURE 1
Blower Assembly
Blower Motor
Capacitor
Internal Flue Pipe
Assembly
Flue Box Gasket
Flue Collector Box
Gasket
Combustion Air Inducer
Gasket
Manifold Burner
Gas Valve
Flame Rollout
Switches
Flame
Sensor
Primary
Limit
Ignitor
Heat Exchanger
Ignitor
Bracket
Combustion Air
Pressure Switch
Combustion
Air Orifice
Gas
Orifices
Flue
Chase
Gasket Limit Sheild with
−3 Units only
Ignition
Control
Transformer
DoorInterlock Switch
Pressure Port
Pressure Port
Location for
−1 to −14 units

Page 9
I−UNIT COMPONENTS
G40DF(X) unit components are shown in figure 1. The gas
valve, combustion air inducer and burners can be ac-
cessed by removing the burner access panel. Electrical
components are in the control box (figure 2) found in the
blower section.
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 2
CONTROL BOX
G40UH(X)
SureLight Control
Transformer
DoorInterlock Switch
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.
3. SureLight Ignition Control (A92) Figure 3
Control 56L84, 10M93 & 32M88
The Lennox SureLight ignition system consists of ignition
control board, ignitor and sensor. The board and ignitor
work in combination to ensure furnace ignition and ignitor
durability. The SureLight integrated board controls all ma-
jor furnace operations. The board also features two LED
lights (DS1, DS2) for troubleshooting and two accessory
terminals rated at (1) one amp. Table 1 gives control termi-
nal designations. Tables 2 and 3 show jack plug terminal
designations. See table 11 for troubleshooting diagnostic
codes. Units equipped with the SureLight board can be
used with either electronic or electro−mechanical thermo-
stats without modification. The SureLight ignitor is made
of durable silicon−nitride. Ignitor longevity is also en-
hanced by voltage ramping by the control board. The
board finds the lowest ignitor temperature which will suc-
cessfully light the burner, thus increasing the life of the ig-
nitor.
TABLE 1
PARK
TERMINAL DESIGNATIONS
COOL−H
HEAT−H
EAC−H
HUM−H
XFMR−H
LINE−H
LINE−N
HUM−N
EAC−N
XFMR−N
CIR−N
Blower − Cooling Speed (120VAC)
Blower − Heating Speed (120VAC)
Electronic Air Cleaner (120VAC)
Humidifier (120VAC)
Transformer (120VAC)
Input (120VAC)
Input (Neutral)
Humidifier (Neutral)
Electronic Air Cleaner (Neutral)
Transformer (Neutral)
Blower − Neutral
(FLAME SENSE)
Alternate Blower Speeds (Dead)
Flame Sensor
120V HOT
120V NEUT

Page 10
SURELIGHT INTEGRATED CONTROL BOARD
FIGURE 3
J156
FLAME SENSE
J58
XFMR−N
TABLE 2
SureLight BOARD J156 (J2) TERMINAL
DESIGNATIONS
PIN # FUNCTION
1Combustion Air Inducer Line
2Ignitor Line
3Combustion Air Inducer Neutral
4Ignitor Neutral
TABLE 3
SureLight BOARD J58 (J1) TERMINAL
DESIGNATIONS
PIN # FUNCTION
1Secondary Limit
2Not Used
324V
4Not Used
5Rollout Switch In
624V
7Primary Limit
8Ground
9Gas Valve In
10 Pressure Switch Out
11 Rollout Switch Out
12 Gas Valve Out
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. Control
10M93 and 32M88 energizes the ignitor during the trial un-
til flame is sensed. Control 56L84 energizes the ignitor for 1
second only. 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. 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.
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.
For customized comfort, monitor the supply air tempera-
ture once the heat demand is satisfied. Note the supply air
temperature at the instant the blower is de−energized. Ad-
just the fan−off delay to achieve a supply air temperature
between 90° − 110° at the instant the blower is de−ener-
gized. (Longer delay times allow for lower air temperature,
shorter delay times allow for higher air temperature). See
figure 4.
FIGURE 4
FAN-OFF TIME ADJUSTMENT
To adjust fan−off timing, flip dip switch to desired setting.
60sec. 90sec. 120sec. 180sec.

Page 11
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.
4. SureLight Ignition Control (A92) Figure 5
Control 69M08
The Lennox SureLight ignition system consists of ignition
control board, ignitor and sensor. The board and ignitor
work in combination to ensure furnace ignition and ignitor
durability. The SureLight integrated board controls all ma-
jor furnace operations. The board also features two LED
lights (DS1 red and DS2 green) for troubleshooting and
two 120 volt accessory terminals, each rated at (1) one
amp. The board also features a 3 amp fuse for low voltage
overcurrent protection. Table 4 gives control terminal des-
ignations. Tables 5 and 6 show jack plug terminal designa-
tions. See table 11 for troubleshooting diagnostic codes.
Units equipped with the SureLight board can be used with
either electronic or electro−mechanical thermostats with-
out modification. The SureLight ignitor is made of durable
silicon−nitride. Ignitor longevity is also enhanced by volt-
age ramping by the control board. The board finds the low-
est ignitor temperature which will successfully light the
burner, thus increasing the life of the ignitor.
TABLE 4
SURELIGHT BOARD TERMINAL DESIGNATIONS
COOL Blower − Cooling Speed (120V)
HEAT Blower − Heating Speed (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 120V Neutral
FS Flamer Sensor
SURELIGHT INTEGRATED CONTROL BOARD
FIGURE 5
3 AMP, 32
VAC FUSE
TABLE 5
SURELIGHT BOARD 4 PIN DESIGNATIONS
PIN # FUNCTION
1Combustion Air Inducer Line
2Ignitor Line
3Combustion Air Inducer Neutral
4Ignitor Neutral
TABLE 6
SURELIGHT BOARD 12 PIN DESIGNATIONS
PIN # FUNCTION
1Prove Switch and Limit Out
2Not Used
324V Hot
4Not Used
5Rollout Switch In 1
624V Common
7Limit In
8Ground
9Gas Valve Common
10 Prove Switch In
11 Rollout Switch Out 2
12 Gas Valve Hot

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−Heating Fan Delay Time
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 7 for switch settings and
fan delay times.
e−Cooling Fan Delay Time
The cooling fan on time is fixed at 2 seconds and cannot be
adjusted. G40DF units do not have a cooling fan off delay
time.
TABLE 7
S1 DIP SWITCH SETTINGS
Heat Off Delay
Switch 1 Switch 2 Seconds
OFF OFF 60
OFF ON 90
ON OFF 120
ON ON 180
5. Ignition Control (A92) Figure 6
Control 78M47 & 100973−01
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 hot surface ignition system consist of an integrated
control board (figure 6 with control terminal designations
in table 10), sensor (figure 9) and ignitor (figure 10). The
control board 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 LED lights (AN1 red and AN2 green) for
troubleshooting and two accessory terminals rated at (1)
one amp. The control board also features a (3) amp fuse for
overcurrent protection. Tables 8 and 9 show jack plug ter-
minal designations. See table 11 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 continuously monitors line voltage and main-
tains the ignitor power at a consistent level to provide
proper lighting and maximum ignitor life.

Page 13
INTEGRATED CONTROL BOARD
FIGURE 6
AN2
GREEN
AN1
RED
TABLE 8
4−Pin Terminal Designation
PIN # FUNCTION
1Combustion Air Inducer Line
2Ignitor Line
3Combustion Air Inducer Neutral
4Ignitor Neutral
TABLE 9
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 10
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 8)
On a call for heat the ignition board monitors the combus-
tion air inducer prove switch. The control board will not be-
gin 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.
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

Page 14
between 90° − 110° at the instant the blower is de−ener-
gized. (Longer delay times allow for lower air temperature,
shorter delay times allow for higher air temperature). See
figure 7. Board 100973−0 only has a 45 second fan off
delay after cooling demand is satisfied. This delay timing is
factory set and non adjustable.
The ignition control boards are equipped with two LED
lights for troubleshooting. The diagnostic codes are listed
in table 11.
FAN-OFF TIME ADJUSTMENT
To adjust fan−off timing, reposition jumper across pins to
achieve desired setting.
FIGURE 7
TABLE 11
DIAGNOSTIC CODES
Make sure to Identify LED’S Correctly.
Refer to figures 3 and 5 for control board layout.
LED #1
DS #1
AN #1
LED #2
DS #2
AN #2
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.
SLOW FLASH OFF Flame sensed without gas valve energized.
ON SLOW FLASH Rollout switch open. OR: 24V 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 18 for flame sense.
ALTERNATING
FAST FLASH
ALTERNATING
FAST FLASH
The following conditions are sensed
Improper main ground (Control 56L84, 10M93, 32M88, 69M08) during ignitor
warm up period ONLY, improper main ground continuously (Control 78M47)
OR: Broken ignitor (Control 56L84, 10M93, 32M88, 69M08)
OR: Open ignitor circuit (Control 56L84, 10M93, 32M88, 69M08)
OR: Line voltage below 75V (Control 56L84, 10M93, 32M88, 69M08)
90V (Control 78M47 & 100973−01)
NOTE − Slow flash rate equals 1 Hz (one flash per second). Fast flash rate equals 3 Hz (three flashes per second).
FIGURE 8
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉ
DEMAND
CAI
GAS VALVE
ON
OFF
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉ
ÉÉÉÉÉÉÉÉÉÉ
IGNITOR*
15 Sec.
Pre −Purge
20 sec.
Ignitor Warm−up
*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
ÉÉÉÉÉÉÉÉÉ
Blower On"
Delay
End of
Heat Demand Blower
Off
Time
* Control 78M47 & 100973−01 will energize ignitor the first 3 seconds of the 4 second trial
56L84, 1 second, 32M88, 69M08 entire trial (4 sec)

Page 15
6.Flame Sensor (Figure 9)
A flame sensor is located on the left side of the burner sup-
port. See parts arrangement figure1. The sensor is
mounted on the flame rollout plate and the tip protrudes
into the flame envelope of the left−most burner. The sensor
can be removed for service without removing any part of
the burners. During operation, flame is sensed by current
passed through the flame and sensing electrode. The igni-
tion control allows the gas valve to remain open as long as
flame signal is sensed. See table 18 for flame sense signal.
FIGURE 9
5/16"
7. Ignitor (Figure 10)
Two type ignitors are used for the SureLight ignition sys-
tem; silicon nitride and mini nitride. The ignition control
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. To
check ignitor, measure its resistance. See table 12 for ohm
value and ignitor control matchup.
TABLE 12
SureLight Control Ignitor Resistance
56L84, 10M93,
32M88, 69M08 Silicon Nitride 10.9 − 19.7
78M47 &
100973−01 Mini Nitride 50 − 450
NOTE − The G40DF(X) furnace contains electronic
components that are polarity sensitive. Make sure that
the furnace is wired correctly and is properly grounded.
8.Blower Motors and Capacitors
All G40DF(X) units use direct drive blower motors. All mo-
tors are 120V permanent split capacitor motors to ensure
maximum efficiency. Ratings for capacitors will be on motor
nameplate.
NOTE − Shafts on 1 HP motors have 2 flat sides and are
matched with blower wheels with 2 set screws.
FIGURE 10
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
9.Flame Rollout Switches (S47)
Flame rollout switch is a high temperature limit located on
top of the burner box. See parts arrangement figure 1. Each
furnace is equipped with two identical switches. One switch
is located over the leftmost burner and the other switch is
located over the rightmost burner. The limit is a N.C. SPST
manual-reset limit connected in series with the ignition con-
trol A92. When S47 senses rollout, the ignition control im-
mediately 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 com-
bustion air. The switch is factory set to open at 210° F and
cannot be adjusted. The switch can be manually reset. To
manually reset a tripped switch, push the reset button located
on the control.
10.Primary Limit Control (S10)
The primary limit (S10) on G40DF(X) units is located in the
heating vestibule panel. G40DF−3 and later models will have
a limit shield. See figure 11 and make note of limit orientation to
shield. 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 auto-
matically resets when unit temperature returns to normal. The
switch must reset within three minutes or SureLight board will
go into Watch guard for one hour. The setpoint is factory set
(printed on side of switch) and cannot be adjusted.

Page 16
FIGURE 11
G40DF−1, −2 UNITS
WITHOUT SHIELD
G40DF UNITS
WITH SHIELD
11.Secondary Limit Controls (S21)
The secondary limit (S21) is an air stream type limit located in
the blower compartment in the back side of the blower hous-
ing. See figure 12. When excess heat is sensed in the blower
compartment, 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. G40DF−1 through −6 units use a 3/4" diameter
limit factory set to open at 150°. G40DF−7 and later units, use
a 1/2" diameter limit factory set to open at 135 °.
FIGURE 12
SUPPLY AIR BLOWER AND SECONDARY LIMIT
SECONDARY
LIMIT
CAPACITOR
MOTOR/BLOWER
ASSEMBLY
To Remove Blower From Unit: Disconnect Power, Remove Control
Box, Remove flue pipe, Remove Bolts and Unplug Motor Wires
From Control Board. Then Slide Out Front of Unit.
12.Gas Valve Figures 13, 14, 15 & 16
The G40DF(X) uses a gas valve manufactured by Honey-
well or White Rodgers. The valve is internally redundant to
assure safety shut−off. If the gas valve must be replaced,
the same type valve must be used.
24VAC terminals and gas control knob 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. Kits 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
FIGURE 13
FIGURE 14
WHITE RODGERS 36F Series Gas Valve
GAS VALVE SHOWN IN OFF POSITION
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
MANIFOLD
PRESSURE
OUTLET
ON
OFF
HONEYWELL VR8205 SERIES GAS VALVE
GAS VALVE SHOWN IN OFF POSITION
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
MANIFOLD
PRESSURE
OUTLET
FIGURE 15
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)
FIGURE 16

Page 17
13.Combustion Air Inducer (B6)
All G40DF(X) units use a combustion air inducer to move
air through the burners and heat exchanger during heating
operation. The blower uses a 120VAC motor. The motor
operates during all heating operation and is controlled by
furnace control A92. The inducer also operates for 15 sec-
onds before burner ignition (pre-purge) and for 5 seconds
after the gas valve closes (post-purge).
A proving switch connected to the combustion air inducer ori-
fice plate (figure 17) is used to prove inducer operation. The
combustion air inducer orifice will be different for each model.
See table 13 for orifice sizes. The switch monitors air pres-
sure in the inducer housing. During normal operation, the
pressure in the housing is negative. If pressure becomes less
negative (signifying an obstruction) the proving switch opens.
When the proving switch opens, the furnace control (A92) im-
mediately closes the gas valve to prevent burner operation.
TABLE 13
G40DF(X) Unit C.A.I. Orifice Size
−045 1.438"
−070 1.688"
−090 1.875"
−110 2.250"
−135 2.600"
FIGURE 17
Flue Box Gasket
Flue Collector Box
Gasket
Combustion
Air Inducer
Combustion Air
Orifice Plate
COMBUSTION AIR INDUCER ASSEMBLY
Prove Switch
*
−1 to −14
pressure
port location
Pressure Port
14.Combustion Air Inducer
Proving Switch (S18)
G40DF(X) series units are equipped with a combustion air
proving switch located on the combustion air inducer orifice
bracket. The switch is connected to the combustion air in-
ducer housing by means of a flexible silicone hose. It moni-
tors negative air pressure in the combustion air inducer
housing.
The switch is a single-pole single-throw proving switch elec-
trically connected to the furnace control. The purpose of the
switch is to prevent burner operation if the combustion air in-
ducer is not operating or if the flue becomes obstructed.
On start-up, the switch senses that the combustion air in-
ducer is operating. It closes a circuit to the furnace control
when pressure inside the combustion air inducer de-
creases to a certain set point. Set points vary depending on
unit size. See table 14. The pressure sensed by the switch
is negative relative to atmospheric pressure. If the flue be-
comes obstructed during operation, the switch senses a
loss of negative pressure (pressure becomes more equal
with atmospheric pressure) and opens the circuit to the fur-
nace control and gas valve. A bleed port on the switch al-
lows relatively dry air in the vestibule to purge switch tub-
ing, 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 14
PROVE SWITCH SET POINTS
Unit 0 − 4500’
(0 − 1372m)
4501’ − 7500’
(1373 −
2286m)
7501’ −
10000’
(2286 −
3098m)
−045−1 to −14 .36" (89Pa) .36" (89Pa) .36" (89Pa)
−070−1 to −14 .36" (89Pa) .36" (89Pa) .36" (89Pa)
−090−1 to −14 .47" (116Pa) .43" (106Pa) .36" (89Pa)
−110−1 to −14 .51" (126Pa) .43" (106Pa) .36" (89Pa)
−135−1 to −14 .51" (126Pa) .47" (116Pa) .43" (106Pa)
ALL −15 and later
models .0.31" (77Pa)
NOTE−Some units require a high altitude pressure
switch kit if installed above 4500 ft (1370 m).

Page 18
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.
G40DF(X) units are equipped with a hot surface igni-
tion 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 bottom access panel.
6 − Close manual main shut off valve. White Rodgers
Gas Valve −− Switch lever to OFF. See figure 13 or
14.
Honeywell Gas Valve −− Turn knob on gas valve
clockwise to OFF. Do not force. See figure 15.
Honeywell Gas Valve with on / off switch, move
switch to OFF. See figure 16.
7 − Wait five (5) minutes to clear out any gas. If you then
smell gas, STOP! Immediately call the 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 − Open manual main shut off valve. White Rodgers Gas
Valve −− Switch gas valve lever to ON.See figure 13 or
14.
Honeywell Gas Valve −− Turn knob on gas valve coun-
terclockwise to ON. See figure 15. Do not force.
Honeywell Gas Valve with on / off switch move
switch to ON. See figure 16.
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" .
To Turn 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. Honeywell Gas Valve with on / off switch,
move switch to OFF. See figure 16.
5 − Replace access panel.
C−Safety or Emergency Shutdown
Disconnect main power to unit. 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
G40DF(X) Installation Instruction.
B−Gas Piping
Gas supply piping should not allow more than 0.5"W.C. drop
in pressure between gas meter and unit. Supply gas pipe
must not be smaller than unit gas connection.
Compounds used on gas piping threaded joints should be
resistant to action of liquefied petroleum gases.
C−Testing Gas Piping
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.
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.
WARNING
Do not exceed 600 in−lbs (50 ft−lbs) torque when
attaching the gas piping to the gas valve.
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 18. 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.

Page 19
FIGURE 18
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 18. 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 15 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 G40DF(X) can be mea-
sured at any time the gas valve is open and is supplying gas
to the unit. See table 15 for normal operating manifold pres-
sure.
TABLE 15
All G40DF 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 13, 14 and 15. Start unit and allow 5
minutes for unit to reach steady state.
2 − While waiting for the unit to stabilize, notice the flame.
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 16 below. Adjust manifold pressure on gas valve to
match time needed. Manifold pressure should not exceed
values listed in table 15. If manifold pressure matches
table 15 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.
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.
TABLE 16
GAS METER CLOCKING CHART
Seconds for One Revolution
G40DF Natural LP
G40DF
Unit 1 cu ft
Dial
2 cu ft
Dial
1 cu ft
Dial
2 cu ft
DIAL
−45 82 164 205 410
−70 55 110 136 272
−90 41 82 102 204
−110 33 66 82 164
−135 27 54 68 136
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 17. The maxi-
mum carbon monoxide reading should not exceed 100
ppm.

FIGURE 19
TRANSDUCER
(PART #78H5401)
Page 20
TABLE 17
Unit CO2%For Nat CO2% For L.P.
24A−45 5.8 − 6.8 6.8 − 7.8
36A−45 5.4 − 6.4 6.10 − 7.10
36A−070 6.6 − 7.6 7.3 − 8.3
36B−090 6.9 − 7.9 8.2 − 9.2
48B−070 6.0 − 7.0 5.7 − 6.7
48C−090 7.2 − 8.2 7.7 − 8.7
48C−110 6.8 − 7.8 7.8 − 8.8
60C−110 6.8 − 7.8 7.8 − 8.8
60D−135 6.9 − 7.9 7.8 − 8.8
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.
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19. The
transducer converts mi-
croamps to volts on a 1:1 conversion. See table 18 for flame
signal A digital readout meter must be used. The transduc-
er plugs into most meters. See figure20 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.
TABLE 18
Flame Signal in Microamps
SureLight
Control Normal Low Drop Out
56L84
10M90
32M88
0.18 0.16 − 0.17 0.15
69M08 0.31 0.25 − 0.30 0.24
78M47
100973−01 1.5 0.5 − 1.4 0.4
SET DIAL TO
MEASURE VDC
(+)
(−)
(−) TO
FLAME
SENSOR
NOTE−MUST USE DIGITAL METER
RED COLLAR
INDICATES
POSITIVE
LEAD
(+) TO
IGNITION
CONTROL
SENSOR
WIRE
FIGURE 20
WARNING
Fire and explosion hazard.
These instructions MUST be followed exactly.
Can cause a fire or explosion resulting in property
damage, personal injury or loss of life.
V−TYPICAL OPERATING CHARACTERISTICS
A−Blower Operation and Adjustment
NOTE− The following is a generalized procedure and
does not apply to all thermostat controls.
1 − Blower operation is dependent on thermostat control
system.
2 − Generally, blower operation is set at thermostat 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.