Lennox Merit ML296UHV Series Installation and operation manual

Page 1
UNIT INFORMATIONUNIT INFORMATION
Service Literature
©2016 Lennox Industries, Inc.
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ON
CCCC
HIHI
IIII
LOLO
HIHI
WARNING
Improper installation, adjustment, alteration,
service or maintenance can cause property damage,
personal injury or loss of life. Installation and service
must be performed by a licensed professional HVAC
installer (or equivalent), service agency or the gas
supplier.
CAUTION
As with any mechanical equipment, contact with
sharp sheet metal edges can result in personal
injury. Take care while handling this equipment and
wear gloves and protective clothing.
ML296UHV(X) series units are 90% e󰀩ciency gas furnac-
es used for downow applications only, manufactured with
Lennox Duralok heat exchangers formed of aluminized
steel. ML296UHV(X) units are available in heating capac-
ities of 44,000 to 110,000 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. ML296U-
HV(X) unit meets the California Nitrogen Oxides (NOx)
Standards and California Seasonal E󰀩ciency require-
ments. All units use a redundant gas valve to assure safe-
ty shut-o󰀨 as required by C.S.A.
All specications in this manual are subject to change.
Procedures outlined in this manual are presented as a
recommendation only and do not supersede or replace lo-
cal or state codes. In the absence of local or state codes,
the guidelines and procedures outlined in this manual (ex-
cept where noted) are recommendations only and do not
constitute code
TABLE OF CONTENTS
Specications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 2
Blower Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 3
I Unit Components . . . . . . . . . . . . . . . . . . . . . . . . Page 9
II Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 21
III Start Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 43
IV Heating System Service Checks . . . . . . . . . Page 44
V Typical Operating Characteristics . . . . . . . . . Page 47
VI Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . Page 47
VII Wiring and Sequence of Operation . . . . . . Page 50
ML296UHV(X)
Corp 1903-L1
Revised 01/2022
ML296UHV(X) SERIES UNITS

Page 2
SPECIFICATIONS
Gas
Heating
Performance
Model No. ML296UH045XV36B ML296UH070XV36B
1 AFUE 96% 96%
High
Fire
Input - Btuh 44,000 66,000
Output - Btuh 42,000 62,000
Temperature rise range - °F 35 - 65 50 - 80
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
3.5 / 10.0 3.5 / 10.0
Low
Fire
Input - Btuh 29,000 43,000
Output - Btuh 28,000 41,000
Temperature rise range - °F 20 - 50 25 - 55
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
1.7 / 4.5 1.7 / 4.5
High static - in. w.g. Heating 0.8 0.8
Cooling 1.0 1.0
Connections
in.
Intake / Exhaust Pipe (PVC) 2 / 2 2 / 2
Gas pipe size IPS 1/2 1/2
Condensate Drain Trap (PVC pipe) - i.d. 3/4 3/4
with furnished 90° street elbow 3/4 slip x 3/4 Mipt 3/4 slip x 3/4 Mipt
with eld supplied (PVC coupling) - o.d. 3/4 slip x 3/4 MPT 3/4 slip x 3/4 MPT
Indoor
Blower
Wheel nominal diameter x width - in. 10 x 9 10 x 9
Motor output - hp 1/2 1/2
Tons of add-on cooling 2 - 3 2 - 3
Air Volume Range - cfm 485 - 1370 500 - 1365
Electrical Data Voltage 120 volts - 60 hertz - 1 phase
Blower motor full load amps 7.7 7.7
Maximum overcurrent protection 15 15
Shipping Data lbs. - 1 package 130 138
NOTE - Filters and provisions for mounting are not furnished and must be eld provided.
1 Annual Fuel Utilization E󰀩ciency based on DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherized
furnaces.
SPECIFICATIONS
Gas
Heating
Performance
Model No. ML296UH090XV48C ML296UH110XV60C
1 AFUE 96% 96%
High
Fire
Input - Btuh 88,000 110,000
Output - Btuh 84,000 106,000
Temperature rise range - °F 45 - 75 45 - 75
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
3.5 / 10.0 3.5 / 10.0
Low
Fire
Input - Btuh 57,000 72,000
Output - Btuh 55,000 70,000
Temperature rise range - °F 30 - 60 35 - 65
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
1.7 / 4.5 1.7 / 4.5
High static - in. w.g. Heating 0.8 0.8
Cooling 1.0 1.0
Connections
in.
Intake / Exhaust Pipe (PVC) 2 / 2 2 / 2
Gas pipe size IPS 1/2 1/2
Condensate Drain Trap (PVC pipe) - i.d. 3/4 3/4
with furnished 90° street elbow 3/4 slip x 3/4 Mipt 3/4 slip x 3/4 Mipt
with eld supplied (PVC coupling) - o.d. 3/4 slip x 3/4 MPT 3/4 slip x 3/4 MPT
Indoor
Blower
Wheel nominal diameter x width - in. 11 x 11 11 x 11
Motor output - hp 3/4 1
Tons of add-on cooling 2.5 - 4 3 - 5
Air Volume Range - cfm 680 - 1770 790 - 1955
Electrical Data Voltage 120 volts - 60 hertz - 1 phase
Blower motor full load amps 10.1 12.8
Maximum overcurrent protection 15 20
Shipping Data lbs. - 1 package 163 174
NOTE - Filters and provisions for mounting are not furnished and must be eld provided.
1 Annual Fuel Utilization E󰀩ciency based on DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherized
furnaces.

Page 3
OPTIONAL ACCESSORIES
NOTE - FURNACES CANNOT BE TWINNED!
“B” Width
Models
“C” Width
Models
CABINET ACCESSORIES
Horizontal Suspension Kit - Horizontal only 51W10 51W10
Return Air Base - Upow only 50W98 50W99
High Performance Economizer (Commercial Only) 10U53 10U53
CONDENSATE DRAIN KITS
Condensate Drain Heat Cable 6 ft. 26K68 26K68
24 ft. 26K69 26K69
Crawl Space Vent Drain Kit US 51W18 51W18
Canada 15Z70 15Z70
CONTROLS
M30 Smart Wi-Fi Thermostat 15Z69 15Z69
¹ Remote Outdoor Temperature Sensor X2658 X2658
Night Service Kit 23H99 23H99
FILTER KITS
2Air Filter and
Rack Kit
Horizontal (end) 87L96 87L97
Size of lter - in. 18 x 25 x 1 20 x 25 x 1
Side Return Single 44J22 44J22
Ten Pack 66K63 66K63
Size of lter - in. 16 x 25 x 1 16 x 25 x 1
TERMINATION KITS
See Installation Instructions for specic venting information.
Direct Vent Concentric US - 2 in. 71M80 69M29
3 in. - - - 60L46
Canada - 2 in. 44W92 44W92
3 in. - - - 44W93
Flush-Mount US - 2, 2-1/2 or 3 in. 51W11 51W11
Canada - 2, 2-1/2 or 3 in. 51W12 51W12
Wall - Close Couple US - 2 in. 22G44 - - -
3 in. 44J40 44J40
Wall - Close Couple WTK Canada - 2 in. 30G28 - - -
3 in. 81J20 81J20
Roof Termination Flashing Kit
(no vent pipe - 2 ashings)
2 in. 15F75 15F75
3 in. 44J41 44J41
VENTING
Flue Coupling 2 in. 17H92 17H92
1 Cleanable polyurethane, frame-type lter.
2 Allows the thermostat to display outdoor temperature. Required in dual-fuel and EDA applications.
NOTE - Termination Kits (44W92, 44W93, 30G28, 51W12, 81J20) and Crawl Space Vent Drain Kit (15Z70) are certied to ULC S636 standard for use in Canada only.

Page 4
BLOWER DATA
ML296UH045XV36B BLOWER PERFORMANCE (less lter)
BOTTOM RETURN AIR, SINGLE SIDE RETURN AIR OR SIDE RETURN AIR WITH OPTIONAL RETURN AIR BASE
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
“ADJUST”
Switch
Positions
Speed Switch Positions
Second Stage “HEAT” Speed - cfm Second Stage “COOL” Speed - cfm
D C 1B A D C B 1A
[phone] 885 1095 1210 1370
1NORM 690 775 855 950 800 990 1115 1255
—610 710 770 845 710 880 995 1115
“ADJUST”
Switch
Positions
First Stage “HEAT” Speed - cfm First Stage “COOL” Speed - cfm
D C 1B A D C B 1A
[phone] 780 900 980
1NORM 640 705 780 840 565 690 800 895
—550 645 700 755 500 615 715 790
1 Factory default jumper setting.
NOTES - The e󰀨ect of static pressure is included in air volumes shown.
First stage HEAT is approximately 91% of the same second stage HEAT speed position.
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan Only speed is approximately 38% of the same second stage COOL speed position.
Lennox Harmony III™ Zoning System Applications - Minimum blower speed is 300 cfm.
ML296UH045XV36B BLOWER MOTOR WATTS (COOLING)
Jumper Speed
Positions
Motor Watts @ Various External Static Pressures - in. wg.
First Stage Second Stage
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
“+” (Plus) SETTING (“Adjust” Jumper at “+” Setting)
“COOL”
Speed
Tap D 20 35 58 79 99 125 148 168 197 63 89 112 140 171 193 222 247 267 295 321
Tap C 49 73 98 120 141 169 187 212 242 123 147 181 209 243 277 301 333 350 390 409
Tap B 73 98 123 148 174 196 225 248 274 171 199 237 268 302 341 371 403 431 459 498
Tap A 93 121 146 182 208 236 261 287 319 250 282 321 360 394 438 474 501 530 529 526
“NORM” (Normal) SETTING (“Adjust” Jumper at “NORM” Setting)
“COOL”
Speed
Tap D 16 42 61 77 98 118 140 167 191 38 60 93 116 141 172 196 219 248 271 294
Tap C 21 42 74 95 126 148 169 194 219 91 116 146 174 211 237 259 291 315 349 369
Tap B 40 61 94 122 149 175 200 223 249 136 161 195 229 260 289 321 346 375 408 435
Tap A 71 98 125 150 174 201 223 254 284 194 222 256 292 324 363 399 426 455 483 515
“—” (Minus) SETTING (“Adjust” Jumper at “—” Setting)
“COOL”
Speed
Tap D 12 33 47 66 85 104 125 149 167 28 51 77 98 120 143 167 193 214 242 260
Tap C 18 46 63 80 101 129 152 171 201 65 91 113 144 172 194 219 245 271 299 321
Tap B 37 59 87 112 133 157 184 205 231 99 126 154 186 209 233 265 293 322 342 377
Tap A 51 73 99 130 152 176 200 223 249 140 169 201 233 265 284 327 349 386 408 444

Page 5
BLOWER DATA
ML296UH070XV36B BLOWER PERFORMANCE (less lter)
BOTTOM RETURN AIR, SINGLE SIDE RETURN AIR OR SIDE RETURN AIR WITH OPTIONAL RETURN AIR BASE
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
“ADJUST”
Switch
Positions
Speed Switch Positions
Second Stage “HEAT” Speed - cfm Second Stage “COOL” Speed - cfm
D C 1B A D C B 1A
[phone] 920 1095 1235 1330
1NORM 880 935 990 1070 840 990 1120 1200
—790 840 890 965 750 885 1000 1075
“ADJUST”
Switch
Positions
First Stage “HEAT” Speed - cfm First Stage “COOL” Speed - cfm
D C 1B A D C B 1A
[phone] 655 780 850 945
1NORM 795 845 900 975 580 700 765 850
—715 770 805 865 515 630 690 760
1 Factory default jumper setting.
NOTES - The e󰀨ect of static pressure is included in air volumes shown.
First stage HEAT is approximately 90% of the same second stage HEAT speed position.
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan Only speed is approximately 38% of the same second stage COOL speed position.
Lennox Harmony III™ Zoning System Applications - Minimum blower speed is 300 cfm.
ML296UH070XV36B BLOWER MOTOR WATTS (COOLING)
Jumper Speed
Positions
Motor Watts @ Various External Static Pressures - in. wg.
First Stage Second Stage
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
“+” (Plus) SETTING (“Adjust” Jumper at “+” Setting)
“COOL”
Speed
Tap D 35 56 79 101 124 146 164 192 214 86 110 139 167 190 223 249 268 297 321 347
Tap C 50 72 103 126 151 174 199 222 243 134 163 196 230 260 295 318 353 381 414 438
Tap B 68 94 118 147 170 197 221 246 274 188 220 256 295 328 362 392 433 461 498 520
Tap A 86 110 146 173 200 224 255 280 306 236 272 311 348 387 418 457 496 529 529 525
“NORM” (Normal) SETTING (“Adjust” Jumper at “NORM” Setting)
“COOL”
Speed
Tap D 24 45 66 89 109 132 151 174 196 65 88 115 146 170 190 219 243 263 287 312
Tap C 40 63 87 112 135 158 180 199 226 99 127 158 187 221 250 277 301 329 357 389
Tap B 58 79 107 130 153 173 198 219 241 147 180 210 245 278 306 340 372 392 421 460
Tap A 69 93 123 154 176 202 228 252 272 185 217 250 288 320 355 388 415 445 471 498
“—” (Minus) SETTING (“Adjust” Jumper at “—” Setting)
“COOL”
Speed
Tap D 22 45 61 77 97 117 144 162 190 53 76 99 123 145 170 194 214 236 262 290
Tap C 27 48 70 96 114 137 157 182 207 74 99 126 157 184 208 234 260 281 312 335
Tap B 37 61 82 104 129 150 174 196 222 105 133 162 194 224 251 280 305 333 357 386
Tap A 45 68 98 123 147 173 195 218 241 162 188 211 229 258 277 307 327 354 379 404

Page 6
BLOWER DATA
ML296UH090XV48C BLOWER PERFORMANCE (less lter)
BOTTOM RETURN AIR, SINGLE SIDE RETURN AIR OR SIDE RETURN AIR WITH OPTIONAL RETURN AIR BASE
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
“ADJUST”
Switch
Positions
Speed Switch Positions
Second Stage “HEAT” Speed - cfm Second Stage “COOL” Speed - cfm
D C 1B A D C B 1A
[phone] 1555 1135 1355 1525 1765
1NORM 1075 1155 1200 1410 1080 1270 1435 1655
—970 1040 1085 1250 940 1115 1255 1460
“ADJUST”
Switch
Positions
First Stage “HEAT” Speed - cfm First Stage “COOL” Speed - cfm
D C 1B A D C B 1A
[phone] 1475 830 985 1095 1260
1NORM 1040 1110 1135 1345 765 920 1040 1195
—935 1000 1030 1210 675 795 900 1040
1 Factory default jumper setting.
NOTES - The e󰀨ect of static pressure is included in air volumes shown.
First stage HEAT is approximately 95% of the same second stage HEAT speed position.
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan Only speed is approximately 38% of the same second stage COOL speed position.
Lennox Harmony III™ Zoning System Applications - Minimum blower speed is 380 cfm.
ML296UH090XV48C BLOWER MOTOR WATTS (COOLING)
Jumper Speed
Positions
Motor Watts @ Various External Static Pressures - in. wg.
First Stage Second Stage
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
“+” (Plus) SETTING (“Adjust” Jumper at “+” Setting)
“COOL”
Speed
Tap D 48 71 94 117 144 164 186 207 234 110 135 165 194 219 243 274 299 330 351 378
Tap C 71 94 121 146 169 193 214 245 266 179 208 240 270 302 329 361 392 422 449 481
Tap B 98 122 154 174 204 228 260 282 305 250 284 314 351 382 412 451 484 517 550 578
Tap A 146 174 202 229 262 286 315 343 372 405 441 481 514 550 584 623 659 701 735 768
“NORM” (Normal) SETTING (“Adjust” Jumper at “NORM” Setting)
“COOL”
Speed
Tap D 44 67 86 105 125 145 169 186 211 105 130 154 178 199 225 250 273 297 324 345
Tap C 65 87 110 131 153 176 197 221 241 158 187 213 242 265 290 314 346 371 404 430
Tap B 90 114 140 163 182 209 229 257 281 215 248 273 301 330 358 380 412 451 473 507
Tap A 133 156 183 208 232 254 278 304 332 335 368 397 428 459 491 519 552 582 611 652
“—” (Minus) SETTING (“Adjust” Jumper at “—” Setting)
“COOL”
Speed
Tap D 23 43 66 88 109 132 152 170 193 67 93 116 139 164 194 218 239 264 286 315
Tap C 38 59 84 109 133 156 176 199 223 110 134 164 187 215 242 268 295 322 346 366
Tap B 55 79 102 131 155 177 207 223 252 143 170 196 230 255 284 311 338 369 394 419
Tap A 85 113 138 162 188 215 242 266 294 220 254 283 315 345 376 416 447 475 510 535

Page 7
BLOWER DATA
ML296UH110XV60C BLOWER PERFORMANCE (less lter)
BOTTOM RETURN AIR, SINGLE SIDE RETURN AIR OR SIDE RETURN AIR WITH OPTIONAL RETURN AIR BASE
NOTE - Air volumes in bold (over 1800 cfm) must have one of the following:
• Single side return air and Optional Return Air Base with transition that must accommodate required 20 x 25 x 1 inch air lter to
maintain proper velocity
• Bottom return air
• Return air from both sides
• Bottom and one side return air
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
“ADJUST”
Switch
Positions
Speed Switch Positions
Second Stage “HEAT” Speed - cfm Second Stage “COOL” Speed - cfm
D C 1B A D C B 1A
[phone] 2105 1405 1620 1820 2055
1NORM 1550 1665 1800 1950 1255 1455 1655 1860
—1400 1505 1625 1750 1145 1335 1515 1700
“ADJUST”
Switch
Positions
First Stage “HEAT” Speed - cfm First Stage “COOL” Speed - cfm
D C 1B A D C B 1A
[phone] 1615 1015 1165 1325 1485
1NORM 1170 1270 1375 1475 905 1055 1200 1335
—1070 1160 1250 1345 800 950 1080 1220
1 Factory default jumper setting.
NOTES - The e󰀨ect of static pressure is included in air volumes shown.
First stage HEAT is approximately 75% of the same second stage HEAT speed position.
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan Only speed is approximately 38% of the same second stage COOL speed position.
Lennox Harmony III™ Zoning System Applications - Minimum blower speed is 460 cfm.
ML296UH110XV60C BLOWER MOTOR WATTS (COOLING)
Jumper Speed
Positions
Motor Watts @ Various External Static Pressures - in. wg.
First Stage Second Stage
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
“+” (Plus) SETTING (“Adjust” Jumper at “+” Setting)
“COOL”
Speed
Tap D 65 90 110 135 155 179 207 228 246 170 196 225 258 286 318 347 380 404 427 456
Tap C 92 120 142 172 196 223 251 274 301 257 286 321 360 391 424 452 484 515 549 585
Tap B 138 162 197 221 251 280 303 334 360 344 379 418 457 494 529 567 602 642 674 713
Tap A 191 220 251 284 312 343 372 401 434 499 539 580 625 661 696 742 783 823 866 902
“NORM” (Normal) SETTING (“Adjust” Jumper at “NORM” Setting)
“COOL”
Speed
Tap D 49 72 94 117 141 160 184 207 231 122 147 177 207 231 261 289 310 342 366 399
Tap C 76 98 126 147 172 196 223 244 267 183 210 244 276 306 334 362 395 422 453 486
Tap B 109 134 160 187 211 237 261 289 313 267 296 334 369 405 434 474 506 538 568 600
Tap A 146 176 200 232 258 287 317 345 370 380 411 457 488 531 565 597 638 672 705 748
“—” (Minus) SETTING (“Adjust” Jumper at “—” Setting)
“COOL”
Speed
Tap D 37 54 83 103 123 147 166 187 206 89 113 138 169 193 217 246 270 293 320 343
Tap C 58 79 103 127 149 175 193 215 239 140 166 198 228 251 280 310 340 364 396 419
Tap B 85 105 136 159 184 207 230 256 278 202 231 266 294 325 359 392 419 447 480 514
Tap A 103 129 154 185 211 237 263 290 312 285 316 349 386 423 453 490 519 552 583 614

Page 8
ML296UHV PARTS IDENTIFICATION
Burner Box Assembly
Gas Valve
Heat Exchanger
Combustion
Air Inducer
Pressure
Switch
Assembly
Primary Limit
Variable Speed Motor
Two-Stage Integrated Control
Access Panel
Bag Assemblies
(shipping location)
Field Make Up Box
Door
Interlock
Switch
16X4W Box
(some models)
Access Panel
FIGURE 1

Page 9
I-UNIT COMPONENTS
Unit components are shown in FIGURE 1. The gas valve,
combustion air inducer and burners can be accessed by
removing the access panel. Electrical components are in
the control box (FIGURE 2) found in the blower section.
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
CAUTION
Electrostatic discharge can a󰀨ect electronic
components. Take precautions to neutralize
electrostatic charge by touching your hand
and tools to metal prior to handling the
control.
A- Control Box
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
secondary.
2. Door Interlock Switch (S51)
A door interlock switch rated 14A at 125VAC is wired in se-
ries with line voltage. When the inner blower access panel
is removed the unit will shut down.
Control Box Components
Integrated Control
Door Interlock Switch
Transformer
FIGURE 2
WARNING
Shock hazard.
Disconnect power before servicing. Integrated
control is not eld repairable. If control is inoperable,
simply replace entire control. Can cause injury
or death. Unsafe operation will result if repair is
attempted.
3. Integrated Control (A92)
Units are equipped with a two-stage, variable speed inte-
grated control. The system consists of a ignition / blower
control (FIGURE 3) with control pin designations in TABLE
3, TABLE 4 and 4 and ignitor. The control and ignitor work
in combination to ensure furnace ignition and ignitor dura-
bility. The control provides gas ignition, safety checks and
indoor blower control with two-stage gas heating. The fur-
nace combustion air inducer, gas valve and indoor blower
are controlled in response to various system inputs such
as thermostat signal, pressure and limit switch signal and
ame signal.
The furnace has a built-in, self-diagnostic capability. If a
system problem occurs, a fault code is shown by a red
LED on the control. The control continuously monitors its
own operation and the operation of the system. If a failure
occurs, the LED will indicate the failure code. The ash
codes are presented in TABLE 2.
Fault Code History Button
The control stores the last ve fault codes in memory. A
pushbutton switch is located on the control. When the
pushbutton switch is pressed and released, the control
ashes the stored fault codes. The most recent fault code
is ashed rst; the oldest fault code is ashed last. To
clear the fault code history, press and hold the pushbutton
switch in for more than 5 seconds before releasing.
Single Stage Thermostat Operation
The automatic heat staging option allows a single stage
thermostat to be used with two stage furnace models. To
activate this option, move the jumper pin (see FIGURE 3)
to desired setting (5 minutes or 10 minutes). The furnace
will start on 1st stage heat and stay at 1st stage heat for
the duration of the selected time before switching to 2nd
stage heat. W1 on the integrated control must be connect-
ed to W1 on the thermostat.
High Heat State LED
A green LED is provided on the control board to indicate
high heat state (see TABLE 1).
CFM LED
An amber LED is provided on the control board to display
CFM. To determine what CFM the motor is delivering at
any time, count the number of times the amber LED ash-
es. Each ash signies 100 CFM; count the ashes and
multiply by 100 to determine the actual CFM delivered (for
example: 5 ashes x 100 = 500 CFM).
TABLE 1
High Heat State Green LED
LED Status Description
LED O󰀨 No demand for high heat
LED On High heat demand, operating normally
LED Flashing High heat demand, high pressure
switch not closed

Page 10
TABLE 2
Diagnostic Codes Red LED
LED Status Description
LED O󰀨 No power to control or control har-
ware fault detected.
LED On Normal operation.
1 Flash Flame present with gas vavle de-en-
ergized.
2 Flashes Pressure switch closed with combus-
tion air inducer de-energized.
3 Flashes Low-re pressure, rollout or limit
switch open.
4 Flashes Primary limit switch open.
5 Flashes Not used
6 Flashes Pressure switch cycle lockout.
7 Flashes Lockout, burners fail to light.
8 Flashes Lockout, buners lost ame too many
times.
9 Flashes Line voltage polarity incorrect.
TABLE 3
Control 5 Pin Terminal Designation
PIN # Function
1Ignitor (Hot)
2Combustion Air Inducer High
Speed
3 Combustion Air Inducer Low Speed
4 Combustion Air Inducer Neutral
5 Ignitor Neutral
Airow Adjustments
Cooling Mode
The units are factory set for the highest airow for each
model. Adjustments can be made to the cooling airow by
repositioning the jumper plug marked COOL – A, B, C, D
(see FIGURE 3). To determine what CFM the motor is de-
livering at any time, count the number of times the amber
LED on the control board ashes. Each ash signies 100
CFM; count the ashes and multiply by 100 to determine
the actual CFM delivered (for example: 5 ashes x 100 =
500 CFM).
Fan on / o󰀨 delay
On a call for heat there is a 30 second fan on delay after
igntion.When the call for heat is satised, the gas valve
and combustion air blower shut down. The circulating air
blower continues to run for selected blower o󰀨 delay time
(60/90/120/180 sec) before ramping down and shutting
o󰀨. The fan on delay is 30 seconds and not adjustabe.
NOTE - The fan o delay on ML296-55 and earlier units is
factory set at 120 seconds and NON- ADJUSTABLE.
TABLE 4
12 Pin Terminal Designation
Pin # Function
1Gas Valve Second Stage
2Second Stage Prove Switch
3 Rollout Switch In
4 Ground
5 24V Hot
6Primary Limit In
7 Gas Valve First Stage
8 Gas Valve Common
924V Neutral
10 Ground
11 Rollout Switch Out
12 First Stage Prove Switch
Heating Mode
These units are factory set to run at the middle of the heat-
ing rise range as shown on the unit rating plate. If higher
or lower rise is desired, reposition the jumper plug marked
HEAT - A, B, C, D (see FIGURE 3) . To determine what
CFM the motor is delivering at any time, count the number
of times the amber LED on the control board ashes. Each
ash signies 100 CFM; count the ashes and multiply by
100 to determine the actual CFM delivered (for example:
5 ashes x 100= 500.
Adjust Tap
Airow amounts may be increased or decreased by 10%
by moving the ADJUST jumper plug (see Figure 3) from
the NORM position to the (+) or (-) position. Changes to
the ADJUST tap will a󰀨ect both cooling and heating air-
ows. The TEST position on the ADJUST tap is not used.
Continuous Blower Operation
The comfort level of the living space can be enhanced
when using this feature by allowing continuous circulation
of air between calls for cooling or heating. The circulation
of air occurs at half the full cooling airow rate.
To engage the continuous blower operation, place the fan
switch on the thermostat into the ON position. A call for fan
from the thermostat closes R to G on the ignition control
board. The control waits for a 1 second thermostat delay
before responding to the call for fan by ramping the circu-
lating blower up to 50% of the cooling speed. When the
call for continuous fan is satised, the control immediately
ramps down the circulating blower.

Page 11
INTEGRATED CONTROL
TERMINAL DESIGNATIONS
HUM -Humidifier (120VAC)
Line - Input (120VAC)
XFMR - Transformer (120VAC)
EAC - Indoor Air Accessory (120VAC)
Cool - Cool Speed (120VAC)
Park 1 - Dead terminal for alternate speed tap
Park 2 - Dead terminal for alternate speed tap
Heat Stage Jumper
(single stage shown)
Heat
Taps
Cool
Taps
Air Flow
Jumper
Fan O Delay
FIGURE 3

Page 12
Power Choke
(5 Ton Only) Blower Motor
(B3)
To Remove Blower From Unit: Remove Bolts and
Wiring Jackplugs. Then Slide Out Front of Unit.
FIGURE 4
Blower Motor (B3)
Blower motors are manufactured by GenTeq and Nidec.
See FIGURE 6 and FIGURE 7. Motors operate the same
and are only di󰀨erent in physical appearance. They are
both three-phase, electronically controlled DC brushless
motors (controller converts single-phase AC to three-
phase DC), with a permanent magnet type rotor. Because
these motors have a permanent magnet rotor it does not
need brushes like conventional DC motors.
Internal components for both manufactured motors are
similarand shown in FIGURE 5. The stator windings are
split into three poles which are electrically connected to
the controller. This arrangement allows motor windings to
turn on and o󰀨 in sequence by the controller.
A solid-state controller is attached to the motor. The con-
troller is primarily an AC to DC converter. Converted DC
power is used to drive the motor. The controller contains a
microprocessor which monitors varying conditions inside
the motor (such as motor workload). The controller on the
NIDEC / Emerson motor includes the 16X4W control with
three LED’s PW, RX and TX located on the face for trou-
bleshooting. FIGURE 7 shows the location of the 16X4W
and TABLE 5 the LED codes. The 16X4W may be located
on the indoor blower housing on some models (FIGURE
8).
BLOWER MOTOR COMPONENTS
STATOR
(WINDINGS)
OUTPUT
SHAFT
BEARING
ROTOR
FIGURE 5
GenTeq BLOWER MOTOR B3
MOTOR
CONTROLLER
J49
J48
FIGURE 6
NIDEC BLOWER MOTOR B3
MOTOR
CONTROLLER
16X4W
(May located
on the blower
housing)
J48
J49
FIGURE 7
16X4W
FIGURE 8
The controller uses sensing devices to sense what posi-
tion the rotor is in at any given time. By sensing the posi-
tion of the rotor and then switching the motor windings on
and o󰀨 in sequence, the rotor shaft turns the blower.
All blower motors use single phase power. An external run
capacitor is not used. The motor uses permanently lubri-
cated ball-type bearings.
Internal Operation
Each time the controller switches a stator winding (FIG-
URE 5) on and o󰀨, it is called a “pulse.” The length of
time each pulse stays on is called the “pulse width.” By
varying the pulse width (FIGURE 11), the controller varies
motor speed (called “pulsewidth modulation”). This allows
for precise control of motor speed and allows the motor to
compensate for varying load conditions as sensed by the
controller. In this case, the controller monitors the static
workload on the motor and varies motor rpm in order to
maintain constant airow (cfm).

Page 13
TABLE 5
Nidec / Emerson Motor Only
PW LED RX LED TX LED Motor Blower Action
O󰀨 Blink Blink Not Rotating Normal
Blink Blink Blink Rotating Normal. PW blink is 100cfm/blink
Blink O󰀨 Blink Not Rotating
Verify 16X4W and motor control hp
match. Verify power to motor control.
Turn o󰀨 power for 1 minute then restart.
If motor still does not rotate replace the
controller.
O󰀨 O󰀨 O󰀨 Not Rotating
Verify power to the 16X4W. Turn o󰀨
power then restart. If LED’s are still out,
replace controller.
Motor rpm is continually adjusted internally to maintain
constant cfm. The controller monitors the static work
load on the motor and motor amp-draw to determine the
amount of rpm adjustment. Blower rpm may be adjusted
any amount in order to maintain a constant cfm as shown
in Blower Ratings Tables. The cfm remains relatively sta-
ble over a broad range of static pressure. Since the blower
constantly adjusts rpm to maintain a specied cfm, motor
rpm is not rated. Hence, the terms “cool speed” , “heat
speed ” or “speed tap” in this manual, on the unit wiring
diagram and on blower B3, refer to blower cfm regardless
of motor rpm.
The unit control indicates the desired cfm. The blower will
maintain the desired cfm as long as external static pres-
sure does not exceed 0.8”. If the system exceeds this
amount, the blower may enter a “cut back”, mode wherein
it then slows down to protect itself from electrical damage.
During this “cut back” mode the unit control will still indi-
cate the same desired cfm regardless of actual motor rpm.
When Harmony is used, speed taps are overridden and
a PWM signal generated by the Harmony controller con-
tinuously varies motor speed based upon zone demands.
Initial Power Up
When line voltage is applied to B3, there will be a large
inrush of power lasting less than 1/4 second. This inrush
charges a bank of DC lter capacitors inside the controller.
If the disconnect switch is bounced when the disconnect is
closed, the disconnect contacts may become welded. Try
not to bounce the disconnect switch when applying power
to the unit.
Motor Start-Up
When B3 begins start-up, the motor gently vibrates back
and forth for a moment. This is normal. During this time
the electronic controller is determining the exact position
of the rotor. Once the motor begins turning, the controller
slowly eases the motor up to speed (this is called “soft-
start”). The motor may take as long as 10-15 seconds to
reach full speed
If the motor does not reach 200rpm within 13 seconds,
the motor shuts down. Then the motor will immediately at-
tempt a restart. The shutdown feature provides protection
in case of a frozen bearing or blocked blower wheel. The
motor may attempt to start eight times. If the motor does
not start after the eighth try, the controller locks out. Reset
controller by momentarily turning o󰀨 power to unit.
The DC lter capacitors inside the controller are connect-
ed electrically to the speed tap wires. The capacitors take
approximately 5 minutes to discharge when the discon-
nect is opened. For this reason it is necessary to wait at
least 5 minutes after turning o󰀨 power to the unit before
attempting to change speed taps.
DANGER
Disconnect power from unit and wait at least
ve minutes to allow capacitors to discharge
before attempting to adjust motor speed tap
settings. Failure to wait may cause personal
injury or death.
External Operation (Speed Tap Priority)
FIGURE 9 and FIGURE 10 shows the two quick-con-
nect jacks (J48 and J49) which connect the motor to the
ML296DFV. Jack J48 is the power plug and jack J49 con-
nects the unit controls to the motor.
Jack J48 is the power plug. Line voltage must be applied
to J48 pins 4 and 5 in order for the motor to operate. When
using 120VAC pins 1 and 2 must be jumpered. Jack J49
connects the unit controls to the motor. The motor assigns
priority to J49 pin 2 so that if a call for cooling and a call
for heating are concurrent, heating call overrides and the
blower operates on high speed heating tap.

Page 14
POWER
CONNECTOR J48
CONTROL
CONNECTOR J49
GenTeq HARNESS CONNECTORS
J49
PIN 1 ‐C1
PIN 2 ‐W / W1
PIN 3 ‐C2
PIN 4 - Delay
PIN 5 ‐Cool
PIN 6 ‐Y1
PIN 7 ‐Adjust
PIN 8 ‐Out
PIN 9 ‐O
PIN 10 ‐
DS(PWM)
PIN 11 ‐Heat
PIN 12 ‐R
PIN 13 ‐EM / W2
PIN 14 ‐Y / Y2
PIN 15 ‐G
PIN 16 ‐Out +
J48
PIN 1 ‐Jumper PIN 1 to PIN2 for 120VAC line input only.
PIN 2 ‐Jumper PIN 1 to PIN2 for 120VAC line input only.
PIN 3 ‐Ground
PIN 4 ‐AC Line
PIN 5 ‐AC Line
1
1
16
FIGURE 9
POWER
CONNECTOR J48
CONTROL
CONNECTOR J49
1
J49
PIN 1 ‐C1
PIN 2 ‐W / W1
PIN 3 ‐C2
PIN 4 - Delay
PIN 5 ‐Cool
PIN 6 ‐Y1
PIN 7 ‐Adjust
PIN 8 ‐Out
PIN 9 ‐O
PIN 10 ‐DS(PWM)
PIN 11 ‐Heat
PIN 12 ‐R
PIN 13 ‐EM / W2
PIN 14 ‐Y / Y2
PIN 15 ‐G
PIN 16 ‐Out +
J48
PIN 1 ‐Jumper PIN 1 to PIN2 for 120VAC line input only.
PIN 2 ‐Jumper PIN 1 to PIN2 for 120VAC line input only.
PIN 3 ‐Ground
PIN 4 ‐AC Line
PIN 5
‐
AC Line
16
1
NIDEC / EMERSON MOTOR
HARNESS CONNECTORS
FIGURE 10
Power Choke (L13)
A choke coil is used on 5 ton 1 hp units. The choke is
located on the blower housing and is used to suppress
transient current spikes.
Precautions
If the furnace or its electronically controlled blower mo-
tor is improperly or inadequately grounded, it may cause
television interference (commonly known as RFI or radio
frequency interference).
This interference is caused by internal switching frequen-
cies of the motor controller. TV interference may show up
as small specks or lines which randomly appear on the
TV screen accompanied by pops or clicks in the sound.
Before attempting any service, make sure the indoor unit
is causing the interference. To check, disconnect power
to indoor unit then check TV for continued signs of inter-
ference.
TV interference may be stopped by making sure the motor
is solidly grounded to the cabinet (metal to metal) and by
making sure the cabinet is solidly grounded. If TV interfer-
ence persists, make sure the television (and all a󰀨ected
RF appliances) are moved away from the furnace. Also
make sure a󰀨ected appliances are connected to a sepa-
rate electrical circuit.

Page 15
One revolution
HIGH SPEED COOL (output from controller to motor windings)
MOTOR SPEED CONTROL WITH D.C. PULSE
‐
WIDTH MODULATION
WINDING #1
WINDING #2
WINDING #3
LOW SPEED HEAT/COOL (output from controller to motor windings)
HIGH SPEED HEAT (output from controller to motor windings)
O volts
325VDC One revolution
O volts
325VDC
O volts
325VDC
WINDING #1
WINDING #2
WINDING #3
O volts
325VDC
O volts
325VDC
O volts
325VDC
WINDING #1
WINDING #2
WINDING #3
O volts
325VDC
O volts
325VDC
O volts
325VDC
Motor speed is determined by the size of the electrical pulse sent to
the motor windings. The longer the pulse, the faster the motor.
One
Pulse
ON PULSE OFF PULSE
WINDINGS TURNED OFF
The frequency of the pulses to the windings is 20KHz.
DO NOT ATTEMPT TO MEASURE THESE VOLTAGES.
WINDINGS TURNED ON
OUTPUT FROM CONTROLLER TO MOTOR WINDINGS
One revolution
FIGURE 11

Page 16
C- Heating Components
1. Ignitor
The ignitor is made of durable silicon nitride. Ignitor lon-
gevity is enhanced by controlling voltage to the ignitor.
The integrated control provides a regulated 120 volts to
the ignitor for a consistent ignition and long ignitor life.
Ohm value should be 39 to 70. See FIGURE 12 for ignitor
location.
NOTE - This furnace contains electronic components that
are polarity sensitive. Make sure that the furnace is wired
correctly and is properly grounded.
2. Flame Sensor
A ame sensor is located on the left side of the burner
support. See FIGURE 12. The sensor tip protrudes into
the ame envelope of the left-most burner. The sensor
can be removed for service without removing any part of
the burners. During operation, ame is sensed by current
passed through the ame and sensing electrode. The
SureLight control allows the gas valve to remain open as
long as ame signal is sensed. See TABLE 6 for ame
signal.
TABLE 6
Flame Signal in Microamps
Normal Low Drop Out
1.5 or greater 1.0 or less 0.5
3. Gas Valve
The valve (gure 50) is internally redundant to assure
safety shut-o󰀨. If the gas valve must be replaced, the
same type valve must be used.
24VAC terminals and gas control knob are located on the
valve. A wire harness connects the terminals from the gas
valve to the electronic ignition control. 24V applied to the
terminals energizes the valve.
Inlet and outlet pressure taps are located on the valve. A
regulator adjustment screw is located on the valve
LPG change over kits are available from Lennox. Kits in-
clude burner orices and a gas valve.
4. Flame Rollout Switches (S47)
Flame rollout switch is a high temperature limit located on
top of the burner box, one on each side.- See FIGURE
12. The limit is a N.C. SPST manual-reset limit. When
S47 senses rollout, the circuit breaks and the ignition con-
trol immediately stops ignition and closes the gas valve.
Rollout can be caused by a blocked heat exchanger, ue
or lack of combustion air. The switch is factory set to trip
(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.
5. Burners
All units use inshot burners. Burners are factory set and
require no adjustment. Always operate the unit with the
burner box front panel in place. Each burner uses an ori-
ce (see table 21 for orice size) that is precisely matched
to the burner input. Burners can be removed as a one
piece assembly for service. If burner assembly has been
removed, it is critical to align center of each burner to the
center of the clamshell when re-installing. See more detail
in Section VI- MAINTENANCE.
6. Primary Limit Control (S10)
The primary limit (S10) is located in the heating 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 min-
utes or the SureLight control will go into Watch guard for
one hour. The switch is factory set and cannot be adjust-
ed. The switch may have a di󰀨erent set point for each unit
model number. See Lennox Repair Parts Handbook if limit
switch must be replaced.

Page 17
HEATING COMPONENTS
Intake Air Top Cap
Sensor
Rollout Switch
Rollout Switch
Burner Assembly
Ignitor
Manifold And Gas Orifices
Two-Stage Gas Valve
Burner Box Cover
FIGURE 12

Page 18
Ignitor Check
Test 1
Check ignitor circuit for correct resistance.
Remove 4-pin plug from control.
Check ohms reading across terminals 1 and 5.
Reading should be between 39 and 70 ohms. If
value is correct, this is the only test needed.
If the reading on the meter is not correct, (0 or
infinity) then a second test is needed.
Test 2
Check ignitor for correct resistance.
Seperate the 2-pin jack-plug near the manifold and check
resistance of ignitor at the plug. Reading should be
between 39 and 70 ohms. If the reading is correct, then
the problem is with the wiring between the jack-plug and
the control. If reading is not correct, the issue is the ignitor.
Test 3
Check ignitor for correct voltage
Insert meter probes into terminals 1 and 5 (use small
diameter probes in order not to damage plug).
Check voltage during 20 second ignitor warm up period.
Voltage should read 120 volts +10%. If voltage reads below
these values, check for correct supply voltage to furnace.
Meter
(set to ohms)
Meter
(set to ohms)
Meter
(set to AC volts)
Integrated Control Detail
Integrated Control Detail
Integrated Control Detail
FIGURE 13

Page 19
7. Combustion Air Inducer (B6) and Cold End Header
Box
All units use a two-stage combustion air inducer to move
air through the burners and heat exchanger during heat-
ing operation. The blower uses a 120VAC motor.
The motor operates during all heating operation and is
controlled by integrated control control A92. The induc-
er also operates for 15 seconds before burner ignition
(prepurge) and for 5 seconds after the gas valve closes
(postpurge). The inducer operates on low speed during
rststage heat, then switches to high speed for second
stage heat.
NOTE - Each furnace model uses a unique CAI. Refer to
Lennox Repair Parts listing for correct inducer for replace-
ment.
The combustion air inducer is installed on the cold end
header box. The cold end header box is a single piece
made of hard plastic. The box has an internal channel
where the combustion air inducer creates negative pres-
sure at unit start up. The channel contains an orice used
to regulate ow created by the combustion air inducer.
The box has pressure taps for the combustion air induc-
er pressure switch hoses. The pressure switch measures
the pressure di󰀨erential across the combustion air inducer
orice or di󰀨erence in the channel and the box. If replace-
ment is necessary the gaskets used to seal the box to
the vestibule panel and the combustion air inducer to
the box, must also be replaced.
A proving switch connected to the combustion air inducer
orice plate is used to prove inducer operation. The com-
bustion air inducer orice will be di󰀨erent for each model.
See TABLE 7 for orice sizes. The pressure switch mea-
sures the pressure di󰀨erential across the combustion air
inducer orice. When the proving switch opens, the fur-
nace control (A92) immediately closes the gas valve to
prevent burner operation.
TABLE 7
ML296UHV(X) Unit C.A.I. Orice Size
-045 0.700
-070 0.920
-090 1.100
-110 1.155
8. Combustion Air Inducer Pressure Switch (S18)
Units are equipped with a dual combustion air pressure
switch (rst and second stage) located on the combustion
air inducer orice bracket. See FIGURE 14. The switch
is connected to the combustion air inducer housing by
means of a exible silicone hose. It monitors negative air
pressure in the combustion air inducer housing.
The switches are a single-pole single-throw proving switch
electrically connected to the integrated control. The pur-
pose of the switch is to prevent burner operation if the
combustion air inducer is not operating or if the ue be-
comes obstructed.On heat demand (rst or second stage)
the switch senses that the combustion air inducer is op-
erating.
It closes a circuit to the integrated control when pressure
inside the combustion air inducer decreases to a certain
set point. Set points vary depending on unit size. See
TABLE 8. The pressure sensed by the switch is nega-
tive relative to atmospheric pressure. If the ue becomes
obstructed during operation, the switch senses a loss of
negative pressure (pressure becomes more equal with at-
mospheric pressure) 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.
COMBUSTION AIR PRESSURE SWITCH
High Fire Switch Low Fire Switch
Positive Port
Negative Port
FIGURE 14
NOTE - The switch is factory set and is not eld adjust-
able. It is a safety shut-down control in the furnace and
must not be by-passed for any reason. If switch is closed
or bypassed, the control will not initiate ignition at start up.
TABLE 8
0 - 4500 ft
Unit Set Point Low Heat Set Point High Heat
-045 0.40 0.70
-070 0.50 0.85
-090 0.50 0.85
-110 0.50 0.90
TABLE 9
4501 - 7500 ft
Unit Set Point Low Heat Set Point High Heat
-045 0.35 0.55
-070 0.45 0.75
-090 0.50 0.85
-110 0.45 0.81
TABLE 10
4501 - 7500 ft
Unit Set Point Low Heat Set Point High Heat
-045 0.35 0.55
-070 0.45 0.75
-090 0.50 0.85
-110 0.45 0.81

Page 20
Pressure Switch Check
To check pressure switch di󰀨erential, refer to FIGURE 15
and use the provided ttings and tubing to follow the steps
below.
1 - Remove thermostat demand and allow unit to cycle
o󰀨.
2 - Remove the tubing from the negative side (red
and black or red) and positive side (black) of the
pressure switch (leave both connected to cold end
header box).
3 - Take the 2” length square tubing and connect to the
positive (+) side of the pressure switch. Take the 10”
length square tubing and tee into the tubing from
the positive side of the cold end header box and
the other side of the 2” square tubing. Connect the
other end of the 10” square tubing the the positive
(+) side of the measuring device.
4 - Take a second piece the 2” length square tubing
and connect to the negative (-) side of the pressure
switch. Take a second piece of 10” length square
tubing and tee into the tubing from the negative (-)
side of the cold end header box and the other side
of the 2” square tubing. Connect the other end of
the 10” square tubing the the negative (-) side of the
measuring device.
5 - Operate unit and observe manometer reading.
Readings will change as heat exchanger warms.
a. Take one reading immediately after start-up.
b. Take a second reading after unit has reached steady
state (approximately 5 minutes). This will be the pressure
di󰀨erential.
The pressure di󰀨erential should be at least 0.15”
greater than those listed in the table 8. Readings in
table are the set points or “break points”.
6 - Remove thermostat demand and allow to cycle o󰀨.
7 - Replace original pressure switch tubing.
NOTE - Pressure dierential values (set point)
in table are the ”break”, or ”open” specications.
”Make”, or ”close” pressure dierentials are 0.15”
greater than the set points listed in table.
PRESSURE SWITCH CHECK
Black Tubing
(positive +)
Red and Black
or Red Tubing
(negative −)
Tee
2” long Square
Tubing
Measuring Device
10” Long Square Tubing
FIGURE 15