Lennox ML193UHE Series User manual

Page 1 ©2019 Lennox Industries Inc.
Litho U.S.A.
Corp. 1905 ML193UHE
Service Literature
ML193UHE SERIES UNITS
ML193UHE series units are high-efficiency gas fur
naces manufactured with Lennox DuralokPlustalumi
nized steel clamshell-type heat exchangers, with a stainless
steel condensing coil. ML193UHE units are available in
heating input capacities of 30,000 to 110,000 Btuh (8.8 to
32.2 kW) and cooling applications from 2 through 5 tons (7.0
through 17.6 kW). Refer to Engineering Handbook for proper
sizing.
Units are factory equipped for use with natural gas. A kit is
available for conversion to LPG operation. All ML193UHE
units are equipped with a hot surface ignition system. The
gas valve is redundant to assure safety shut-off as re
quired by C.S.A.
The heat exchanger, burners and manifold assembly can be
removed for inspection and service. The maintenance section
gives a detailed description on how this is done.
The ML193UHE can be “twinned” with a second unit. See
twinning kit 16W72 for information for two units to operate
as one, in a shared duct system controlled by a single ther
mostat.
All specifications are subject to change. Procedures outlined
in this manual are presented as a recommendation only
and do not supersede or replace local or state codes.
WARNING
Electric shock hazard. Can cause injury
or death. Before attempting to perform
any service or maintenance, turn the
electrical power to unit OFF at discon
nect switch(es). Unit may have multiple
power supplies.
Table of Contents
Specifications 2.................................
Optional Accessories 4..........................
Blower Performance Data 5......................
I-Unit Components 7............................
II Placement and Installation 20....................
III-Start-Up 39...................................
IV-Heating System Service Checks 40..............
V-Typical Operating Conditions 44.................
VI-Maintenance 45...............................
VII-Sequence of Operation and Flow Charts 48......
WARNING
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 licensed professional HVAC in
staller (or equivalent), service agency or the gas sup
plier.
CAUTION
As with any mechanical equipment, contact with
sharp sheet metal edges can result in personal in
jury. Take care while handling this equipment and
wear gloves and protective clothing.

Page 2
SPECIFICATIONS
Gas
Heating
Performance
Model No. ML193UH030XE36B ML193UH045XE36B ML193UH070XE36B ML193UH090XE36C
AHRI Reference No. 20256877 20256878 20256879 20256880
1AFUE 93% 93% 93% 93%
Input - Btuh 30,000 44,000 66,000 88,000
Output - Btuh 29,000 42,000 63,000 84,000
Temperature rise range - °F 25 - 55 30 - 60 40 - 70 50 - 80
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
3.5 / 10 3.5 / 10.0 3.5 / 10.0 3.5 / 10
High static - in. w.g. 0.5 0.5 0.5 0.5
Connections
in.
Intake / Exhaust Pipe (PVC) 2 / 2 2 / 2 2 / 2 2 / 2
Gas pipe size IPS 1/2 1/2 1/2 1/2
Condensate Drain Trap (PVC pipe) - i.d. 3/4 3/4 3/4 3/4
with furnished 90° street elbow 3/4 slip x 3/4 Mipt 3/4 slip x 3/4 Mipt 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 3/4 slip x 3/4 MPT 3/4 slip x 3/4 MPT
Indoor
Blower
Wheel nom. dia. x width - in. 10 x 8 10 x 8 10 x 8 10 x 8
Motor Type DC Brushless DC Brushless DC Brushless DC Brushless
Motor output - hp 1/2 1/2 1/2 1/2
Tons of add-on cooling 1.5 - 3 1.5 - 3 1.5 - 3 1.5 - 3
Air Volume Range - cfm 175 - 1435 355 - 1420 355 - 1430 405 - 1410
Electrical
Data
Voltage 120 volts - 60 hertz - 1 phase
Blower motor full load amps 6.8 6.8 6.8 6.8
Maximum overcurrent protection 15 15 15 15
Shipping Data lbs. - 1 package 120 120 127 144
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. ML193UH090XE48C ML193UH110XE48C ML193UH110XE60C
AHRI Reference No. 20256881 20256882 20256883
1AFUE 93% 93% 93%
Input - Btuh 88,000 110,000 110,000
Output - Btuh 84,000 104,000 105,000
Temperature rise range - °F 45 - 75 50 - 80 45 - 75
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
3.5 / 10.0 3.5 / 10 3.5 / 10
High static - in. w.g. 0.5 0.5 0.5
Connections
in.
Intake / Exhaust Pipe (PVC) 2 / 2 2 / 2 2 / 2
Gas pipe size IPS 1/2 1/2 1/2
Condensate Drain Trap (PVC pipe) - i.d. 3/4 3/4 3/4
with furnished 90° street elbow 3/4 slip x 3/4 Mipt 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 3/4 slip x 3/4 MPT
Indoor
Blower
Wheel nom. dia. x width - in. 10 x 10 10 x 10 11-1/2 x 10
Motor Type DC Brushless DC Brushless DC Brushless
Motor output - hp 3/4 3/4 1
Tons of add-on cooling 2.5 - 4 2.5 - 4 3 - 5
Air Volume Range - cfm 830 - 1710 850 - 1750 1085 - 2150
Electrical
Data
Voltage 120 volts - 60 hertz - 1 phase
Blower motor full load amps 8.4 8.4 10.9
Maximum overcurrent protection 15 15 15
Shipping Data lbs. - 1 package 144 156 158
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
“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
Blower Relay Kit (for two-stage outdoor units) 85W66 85W66
iComfort® M30 Smart Wi-Fi Thermostat 15Z69 15Z69
Remote Outdoor Temperature Sensor X2658 X2658
Twinning Kit 16W72 16W72
FILTER KITS
1Air Filter and
Rack Kit
Horizontal (end) Size of lter - in. 87L96 - 18 x 25 x 1 87L97 - 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
NIGHT SERVICE KIT
Night Service Kit 84W48 84W48
TERMINATION KITS
See Installation Instructions for specic venting information.
Termination Kits -
Direct Vent
Applications Only
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
Termination Kits -
Direct or Non-
Direct vent
Roof 2 in. 15F75 15F75
Wall Ring Kit 2 in. 15F74 315F74
2Roof Termination Flashing Kit - Direct or Non-
Direct Vent (2 ashings)
2 in. 44J41 44J41
VENTING
Flue Coupling 2 in. 17H92 17H92
1 Cleanable polyurethane frame type lter.
2 Kits contain enough parts for two, non−direct vent installations.
3Non-direct vent only.
NOTE - Termination Kits (44W92, 44W93, 30G28, 51W12, 51W19, 81J20) and Crawl Space Vent Drain Kit (15Z70) are certied to ULC S636 standard for use in
Canada only.

Page 4
BLOWER DATA
ML193UH045XE36B PERFORMANCE (Less Filter)
External
Static
Pressure
in. w.g.
Air Volume / Watts at Various Blower Speeds
High Medium-High Medium Medium-Low Low
cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts
0.00 1420 343 1305 264 1170 191 930 102 780 66
0.10 1390 348 1270 271 1135 199 885 109 735 71
0.20 1355 349 1230 280 1100 207 850 119 680 81
0.30 1330 368 1205 291 1060 220 795 126 625 84
0.40 1295 378 1180 298 1025 226 755 134 570 91
0.50 1265 386 1140 310 995 233 720 140 515 95
0.60 1240 402 1100 316 955 242 670 148 475 104
0.70 1210 411 1065 331 920 253 615 157 425 107
0.80 1160 420 1030 340 880 262 580 160 355 114
ML193UH070XE36B PERFORMANCE (Less Filter)
External
Static
Pressure
in. w.g.
Air Volume / Watts at Various Blower Speeds
High Medium-High Medium Medium-Low Low
cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts
0.00 1430 330 1300 249 1170 185 955 101 750 67
0.10 1395 337 1270 256 1145 192 910 107 705 71
0.20 1365 344 1245 269 1100 199 865 115 655 76
0.30 1340 357 1215 275 1080 210 815 123 600 82
0.40 1305 367 1180 285 1040 219 760 133 550 93
0.50 1270 377 1145 296 1005 230 720 139 505 95
0.60 1250 393 1110 305 970 237 685 147 455 100
0.70 1210 401 1080 316 930 247 635 152 405 109
0.80 1185 412 1045 325 885 255 600 158 355 114
ML193UH030XE36B PERFORMANCE (Less Filter)
External
Static
Pressure
in. w.g.
Air Volume / Watts at Various Blower Speeds
High Medium-High Medium Medium-Low Low
cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts
0.00 1435 346 1170 191 1000 127 775 62 705 45
0.10 1400 351 1130 199 955 132 735 71 635 48
0.20 1360 358 1085 207 905 137 680 81 515 50
0.30 1325 370 1055 217 865 148 625 84 445 55
0.40 1300 382 1020 227 815 157 570 91 380 61
0.50 1265 387 990 231 785 161 515 95 310 66
0.60 1235 402 945 244 735 168 475 104 265 68
0.70 1200 411 910 253 710 175 425 107 215 72
0.80 1160 420 885 260 660 183 355 114 175 75
ML193UH090XE36C PERFORMANCE (Less Filter)
External
Static
Pressure
in. w.g.
Air Volume / Watts at Various Blower Speeds
High Medium-High Medium Medium-Low Low
cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts
0.00 1410 280 1340 230 1160 160 835 90 770 64
0.10 1375 289 1315 239 1125 168 885 95 730 70
0.20 1340 301 1285 249 1090 175 840 104 685 74
0.30 1310 314 1260 261 1055 180 780 112 645 81
0.40 1275 326 1225 269 1015 195 730 117 590 87
0.50 1240 340 1190 279 965 201 675 126 535 91
0.60 1210 347 1160 288 920 211 620 133 495 98
0.70 1170 362 1130 299 885 221 580 138 455 102
0.80 1135 368 1105 304 855 229 535 144 405 107

Page 5
BLOWER DATA
ML193UH110XE60C PERFORMANCE (Less Filter)
External
Static
Pressure
in. w.g.
Air Volume / Watts at Di󰀨erent Blower Speeds
Bottom Return Air, Side Return Air with Return Air from Both
Sides or Return Air from Bottom and One Side.
Single Side Return Air − Air volumes in bold (over 1800
cfm) require Optional Return Air Base and eld fabricated
transition to accommodate 20 x 25 x 1 in. air lter in order to
maintain proper air velocity.
High Med-High Medium Med-Low Low High Med-High Medium Med-Low Low
cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts
0.00 2150 624 1915 436 1755 345 1650 280 1480 201 2175 607 1930 412 1760 330 1645 271 1475 199
0.10 2120 633 1880 441 1715 353 1605 288 1435 210 2135 614 1885 421 1705 342 1595 280 1415 207
0.20 2085 648 1830 455 1665 362 1560 298 1360 220 2085 628 1830 437 1670 351 1545 293 1370 218
0.30 2040 663 1795 468 1630 374 1515 317 1325 229 2035 647 1790 451 1625 364 1500 308 1315 227
0.40 2005 675 1760 482 1585 386 1470 327 1270 244 1995 657 1755 469 1590 378 1460 319 1275 240
0.50 1965 688 1710 496 1540 399 1425 336 1230 251 1985 674 1725 478 1545 391 1410 329 1225 250
0.60 1935 705 1680 507 1510 408 1390 347 1180 263 1925 687 1675 494 1495 401 1375 343 1170 257
0.70 1885 715 1635 521 1485 425 1345 359 1140 271 1900 698 1635 506 1450 413 1330 351 1125 270
0.80 1855 735 1600 534 1440 426 1305 367 1085 279 1850 711 1605 520 1415 430 1285 363 1075 281
ML193UH090XE48C PERFORMANCE (Less Filter)
External
Static
Pressure
in. w.g.
Air Volume / Watts at Various Blower Speeds
High Medium-High Medium Medium-Low Low
cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts
0.00 1710 373 1500 256 1395 200 1315 164 1205 129
0.10 1675 381 1475 263 1365 206 1275 173 1160 135
0.20 1655 392 1460 273 1315 219 1230 185 1110 142
0.30 1615 408 1410 282 1290 225 1195 192 1065 151
0.40 1595 416 1365 295 1245 236 1155 203 1010 160
0.50 1560 429 1335 308 1200 246 1105 214 965 167
0.60 1525 439 1295 315 1160 255 1060 221 915 176
0.70 1490 453 1260 325 1105 268 1015 229 875 184
0.80 1445 464 1230 332 1085 275 980 240 830 195
ML193UH110XE48C PERFORMANCE (Less Filter)
External
Static
Pressure
in. w.g.
Air Volume / Watts at Various Blower Speeds
High Medium-High Medium Medium-Low Low
cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts
0.00 1750 372 1535 254 1410 200 1330 169 1220 128
0.10 1715 380 1495 262 1380 208 1295 176 1175 135
0.20 1680 391 1470 272 1355 220 1255 184 1135 145
0.30 1640 405 1425 284 1300 230 1220 194 1085 154
0.40 1615 418 1395 296 1260 239 1170 206 1025 162
0.50 1580 433 1345 305 1225 249 1130 212 975 170
0.60 1540 445 1315 315 1180 258 1080 223 935 179
0.70 1515 450 1285 325 1135 268 1035 230 895 186
0.80 1470 467 1230 334 1095 278 995 240 850 192

Page 6
ML193UHE PARTS IDENTIFICATION
FIGURE 1
TOP CAP
BURNER BOX
ASSEMBLY
DuralokPlusTM
HEAT EXCHANGER
ASSEMBLY
CONTROL BOX
(includes integrated ignition control, trans
former, circuit breaker and interlock switch)
COMBUSTION AIR
INDUCER
BURNER
ACCESS
PANEL
COMBUSTION
AIR PRESSURE
SWITCH
PRIMARY LIMIT
GAS VALVE
BLOWER
ASSEMBLY
FLEXIBLE NO-HUB
EXHAUST COLLAR
COLD END
HEADER BOX
BAG ASSEMBLIES
(shipping location)
BLOWER
ACCESS
PANEL

Page 7
I-UNIT COMPONENTS
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
CAUTION
Electrostatic discharge can affect elec
tronic components. Take precautions
to neutralize electrostatic charge by
touching your hand and tools to metal
prior to handling the control.
ML193UHE unit components are shown in figure 1. The
combustion air inducer, gas valve and burners can be ac
cessed by removing the burner access panel. The blower
and control box can be accessed by removing the blow
er access door.
A-Control Box Components (Figure 2)
Unit transformer (T1) and integrated ignition control (A92)
are located in the control box. In addition, a door interlock
switch (S51) is located in the control box.
FIGURE 2
ML193UHE Control Box
Integrated Control
Door Interlock
Switch
Transformer
Circuit Breaker
1. Transformer (T1)
A transformer located in the control box provides power to
the low voltage section of the unit. The transformers on all
models are rated at 40VA with a 120V primary and 24V
secondary.
2. Door Interlock Switch (S51)
A door interlock switch rated 14A at 120VAC is located on
the control box. The switch is wired in series with line volt
age. When the blower door is removed the unit will shut
down.
3. Circuit Breaker (CB8)
A 24V circuit breaker is also located in the control box. The
switch provides overcurrent protection to the transformer
(T1). The breaker is rated at 3A at 32V. If the current ex
ceeds this limit the breaker will trip and all unit operation will
shutdown. The breaker can be manually reset by pressing
the button on the face.
4. Integrated Ignition Control (A92)
WARNING
Shock hazard.
Disconnect power before servicing. Control is not
field repairable. If control is inoperable, simply re
place entire control.
Can cause injury or death. Unsafe operation will re
sult if repair is attempted.
The hot surface ignition control system consisting of an in
tegrated control (figure 3 with control terminal designa
tions in tables 1, 2 and 3), sensor and ignitor (figure 5). The
integrated control and ignitor work in combination to en
sure furnace ignition and ignitor durability. The integrated
control, controls all major furnace operations. The inte
grated control also features a RED LED for troubleshoot
ing and two accessory terminals rated at (1) one amp. See
table 4 for troubleshooting diagnostic codes. The nitride
ignitor is made from a non-porous, high strength propri
etary ceramic material that provides long life and trouble
free maintenance.
TABLE 1
4-Pin Terminal Designation
PIN # FUNCTION
1Combustion Air Inducer Line
2Ignitor Line
3Combustion Air Inducer Neutral
4Ignitor Neutral
TABLE 2
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 Pressure Switch In
11 Rollout Switch In
12 Gas Valve Out

Page 8
TABLE 3
1/4” QUICK CONNECT TERMINALS
120HUM Humidifier 120VAC
LINE 120VAC
XFMR Transformer 120VAC
CIRC Indoor blower 120VAC
EAC Indoor air quality accessory 120VAC
NEUTRALS Common 120VAC
HUM24 Humidifier 24VAC
3/16” QUICK CONNECT TERMINALS
COOL Cooling tap 24VAC
HEAT Heating tap 24VAC
FAN Continuous blower 24 VAC
PARK (no power) Park terminal for unused speed taps
FS Flame sense
24 COM Common 24VAC
TABLE 4
The integrated control is equipped with an LED light for troubleshooting. The diagnostic codes are listed below in table 4.
RED LED
Flash Code 2Diagnostic Codes / Status of Furnace
Off No power to control or board fault detected
Heartbeat1Normal Operation - Idle, Continuous Fan, Cool
Continuous Rapid
Flash Call For Heat / Burner Operation
1Reverse Line Voltage Polarity
2Improper Earth Ground
3Burner failed to light, or lost flame during heat demand
4Low Flame Signal - check flame sensor
5Watchguard - burner failed to light, exceeded maximum number of retries or recycles.
6Not Used
7Primary or Secondary Limit Open or Watchguard Mode - Limit Switch Open longer than 3 min
utes
8Rollout Switch Open
9Pressure Switch failed to close or opened during heat demand
10 Watchguard - Pressure Switch opened 5 times during one heat demand
11 Pressure Switch stuck closed prior to activation of combustion air inducer
12 Flame Sensed without gas valve energized
13 Low Line Voltage
Notes
Note 1 A ”Heartbeat” is indicated by a ”Slow Flash” - 1 sec on 1 sec off, repeating
Note 2 Error codes are indicated by a ”Rapid Flash” - the LED flashes X times at 1/2 sec on 1/2 sec
off, remains off for 3 sec, then repeats
Note 3
Last 10 error codes are stored in memory including when power is shut off to the unit. - To recall,
press and release button, most recent will be displayed first, LED off for 3 sec, then next error
code is displayed, etc. To clear error codes, depress and hold button longer than 5 seconds.

Page 9
FIGURE 3
INTEGRATED CONTROL
(Automatic Hot Surface Ignition System)
BLOWER OFF DELAY
RED LED RECALL BUTTON
Electronic Ignition
On a call for heat the integrated control monitors the com
bustion air inducer pressure switch. The control board will
not begin the heating cycle if the pressure switch is closed
(by-passed). Once the pressure switch is determined to be
open, the combustion air inducer is energized. When the
differential in the pressure switch is great enough, the pres
sure switch closes and a 15-second pre-purge begins. If
the pressure switch is not proven within 2-1/2 minutes, the
integrated control goes into Watchguard-Pressure Switch
mode for a 5-minute 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 inte
grated control will try four more times with an inter purge
and warm-up time between trials of 35 seconds. After a to
tal of five trials for ignition (including the initial trial), the inte
grated control goes into Watchguard-Flame Failure mode.
After a 60-minute reset period, the integrated control will
begin the ignition sequence again.
Fan Time Control
Heating Fan On Time
The fan on time of 30 seconds is not adjustable.
Heating Fan Off Time
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 fac
tory fan off setting of 90 seconds. For customized comfort,
monitor the supply air temperature once the heat demand
is satisfied. Note the supply air temperature at the instant
the blower is de-energized.
Adjust the fan-off delay to achieve a supply air temperature
between 90° - 110° at the instant the blower is de-ener
gized. (Longer delay times allow for lower air temperature,
shorter delay times allow for higher air temperature). See
figure 4.
Cooling Fan On Time
The fan on time is 2 seconds and is not adjustable.
Cooling Fan Off Time
The control has a 45 second fan off delay after cooling de
mand has been met. This delay is factory set and not ad
justable.
HEAT FAN‐OFF TIME IN SECONDS
To adjust fan-off timing, reposition jumper across pins to
achieve desired setting.
NO JUMPER
FIGURE 4
60 90
120
180
60 90
120
180
60 90
120
180
60 90
120
180
60 Second
off Time
90 Second
off Time
120 Second
off Time
180 Second
off Time
CAUTION
Electrostatic discharge can affect elec
tronic components. Take precautions
to neutralize electrostatic charge by
touching your hand and tools to metal
prior to handling the control.
WARNING
Shock hazard.
Disconnect power before servicing. Control is not
field repairable. If control is inoperable, simply re
place entire control.
Can cause injury or death. Unsafe operation will
result if repair is attempted.

Page 10
FIGURE 5
ML193UHE Burner Box Assembly
Gas Valve
Burner Box Front
Rollout Switch(s)
Flame Sensor
Ignitor
Burner Assembly
B-Heating Components
Combustion air inducer (B6), primary limit control (S10), ig
nitor, burners, flame rollout switch (S47), gas valve (GV1),
combustion air pressure switch (S18), and heat exchangers
are located in the heating compartment. The heating com
partment can be accessed by removing the outer access
panel.
1. Flame Rollout Switches (Figure 5)
Flame rollout switches S47 are SPST N.C. high temperature
limits located on the left and right of the front buner box plate.
S47 is wired to the burner ignition control A92. When ei
ther of the switches sense flame rollout (indicating a
blockage in the combustion passages), the flame rollout
switch trips, and the ignition control immediately closes
the gas valve. Switch S47 in all ML193UHE units is factory
preset to open at 210_F + 12_F (99_C + 6.7_C) on a tem
perature rise. All flame rollout switches are manual reset. See
table 4 flash code 8 for troubleshooting.
2. Heat Exchanger (Figure 6)
ML193UHE units use an aluminized steel primary and
stainless steel secondary heat exchanger assembly.
Heat is transferred to the air stream from all surfaces of
the heat exchanger. The shape of the heat exchanger en
sures maximum efficiency.
The combustion air inducer pulls fresh air through the burn
er box. This air is mixed with gas in the burners. The gas /
air mixture is then burned at the entrance of each
clamshell. Combustion gases are then pulled through the pri
mary and secondary heat exchangers and exhausted out the
exhaust vent pipe.
3. Primary Limit Control (Figure 6)
Primary limit (S10) used on ML193UHE units is located in the
heating vestibule panel. When excess heat is sensed in the
heat exchanger, the limit will open. Once the limit opens, the
furnace control energizes the supply air blower and de-en
ergizes the gas valve. The limit automatically resets when
unit temperature returns to normal. The switch is factory
set and cannot be adjusted. For limit replacement remove
wires from limit terminals, remove mounting screws, rotate
limit switch 90 degrees and slowly remove from the
vestibule panel. Install replacement limit with same care.
See table 4 flash code 7 for troubleshooting if limit
switch opens during operation.