Lennox ML180DF045P24A Installation and operation manual

Page 1 ©2013 Lennox Industries Inc.
ML180DF(X)
Service Literature
Corp. 1219-L4
Revised 02/2013
ML180DF series units are mid-efficiency gas furnaces
used for downflow applications only, manufactured with
Lennox Duraloktheat exchangers formed of aluminized
steel. ML180DF units are available in heating capacities of
44,000 to 110,000 Btuh and cooling applications 1.5 to 5
tons. Refer to Product Specifications bulletin for proper siz
ing.
Units are factory equipped for use with natural gas. Kits are
available for conversion to LP/Propane operation.
ML180DF model units are equipped with a hot surface igni
tion system. 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
Specifications Page 2.............................
Blower Data Page 4..............................
Parts Identification Page 5.........................
I Unit Components Page 6........................
II Installation Page 14.............................
III Start Up Page 14..............................
IV Heating System Service Checks Page 14.........
V Typical Operating Characteristics Page 19.........
VI Maintenance Page 19..........................
VII Wiring and Sequence of Operation Page 22......
VIII Twinning Page 27.............................
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
Performance
Model No.
Model No. - Low NOx
ML180DF045P24A
- - -
ML180DF045P36A
- - -
ML180DF070P36A
ML180DF070XP36A
1AFUE 80% 80% 80%
Input - Btuh 44,000 44,000 66,000
Output - Btuh 35,000 36,000 53,000
Temperature rise range - °F 25 - 55 15 - 45 25 - 55
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
3.5 / 10.0 3.5 / 10.0 3.5 / 10.0
High Static - in. w.g. 0.50 0.50 0.50
Connections
in.
Flue connection - in. round 4 4 4
Gas pipe size IPS 1/2 1/2 1/2
Indoor
Blower
Wheel nom. dia. x width - in. 10 x 7 10 x 8 10 x 8
Motor output - hp 1/5 1/3 1/3
Tons of add-on cooling 1.5 - 2 2 - 3 2 - 3
Air Volume Range - cfm 401 - 1157 739 - 1524 717 - 1562
Electrical
Data
Voltage 120 volts - 60 hertz - 1 phase
Blower motor full load amps 3.1 6.1 6.1
Maximum overcurrent protection 15 15 15
Shipping Data lbs. - 1 package 105 113 128
NOTE - Filters and provisions for mounting are not furnished and must be eld provided.
1 Annual Fuel Utilization Ef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.
Model No. - Low NOx
ML180DF090P36B
- - -
ML180DF090P48B
ML180DF090XP48B
ML180DF110P60C
ML180DF110XP60C
1AFUE 80% 80% 80%
Input - Btuh 88,000 88,000 110,000
Output - Btuh 71,000 71,000 89,000
Temperature rise range - °F 35 - 65 25 - 55 30 - 60
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
3.5 / 10.0 3.5 / 10.0 3.5 / 10.0
High Static - in. w.g. 0.50 0.50 0.50
Connections
in.
Flue connection - in. round 4 4 4
Gas pipe size IPS 1/2 1/2 1/2
Indoor
Blower
Wheel nom. dia. x width - in. 10 x 9 10 x 10 11-1/2 x 10
Motor output - hp 1/3 1/2 1
Tons of add-on cooling 2 - 3 3 - 4 4 - 5
Air Volume Range - cfm 743 -1695 917 - 1929 1517 - 2760
Electrical
Data
Voltage 120 volts - 60 hertz - 1 phase
Blower motor full load amps 6.1 8.2 10.0
Maximum overcurrent protection 15 15 15
Shipping Data lbs. - 1 package 131 140 160
NOTE - Filters and provisions for mounting are not furnished and must be eld provided.
1 Annual Fuel Utilization Efciency based on DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherized furnaces.

Page 3
HIGH ALTITUDE DERATE
NOTE - Units may be installed at altitudes up to 4500 ft. above sea level without any modications.
At altitudes above 4500 ft. units must be derated to match information in the shaded areas shown below.
NOTE - This is the only permissible derate for these units.
Input
Gas Manifold Pressure (Outlet) in. w.g. Line Pressure - in. w.g.
0 - 4500 Feet 4501 - 7500 Feet 7501 - 10,000 ft. Minimum
Maximum
Natural
Gas
LPG/
Propane
Natural
Gas
LPG/
Propane
1Natural
Gas
LPG/
Propane
Natural
Gas
LPG/
Propane
045 3.5 10 3.5 10 3.5 10 4.5 11 13
070 3.5 10 3.3 10 3.5 10 4.5 11 13
090 3.5 10 3.3 10 3.5 10 4.5 11 13
110 3.5 10 3.3 10 3.5 10 4.5 11 13
1 Natural Gas High Alitude Orice Kit required.
OPTIONAL ACCESSORIES - ORDER SEPARATELY
“A” Width
Models
“B” Width
Models
“C” Width
Models
CABINET ACCESSORIES
Downow Combustible Flooring Base 11M59 11M60 11M61
CONTROLS
Twinning Kit 15L38 15L38 15L38
FILTERS
1 Downow Filter Cabinet 51W06 51W07 51W08
No. and Size of lter - in. (1) 20 x 20 x 1 (2) 20 x 16 x 1 (2) 20 x 16 x 1
service kits
Night Service Kit 51W03 51W03 51W03
Universal Service Kit - Switches 89W19 89W19 89W19
1 Cleanable polyurethane, frame-type lter.
GAS HEAT ACCESSORIES
Input
High Altitude
Pressure Switch Kit
Natural Gas to
LPG/Propane Kit
LPG/Propane
to Natural Gas Kit
Natural Gas
High Altitude
Orice Kit
0 - 4500 ft. 4501 - 7500 ft. 7501 - 10,000 ft. 0 - 7500 ft. 7501 - 10,000 ft. 0 - 7500 ft. 7501 - 10,000 ft.
045 No Change No Change 80W51 70W89 76W15 73W81 73W37
070 No Change 80W52 80W51 70W89 76W15 73W81 73W37
090 No Change No Change 80W51 70W89 76W15 73W81 73W37
110 No Change 80W52 80W51 70W89 76W15 73W81 73W37
INSTALLATION CLEARANCES
Vent Type Type B1 Type C NOTE − Air for combustion must conform to the methods outlined in the
National Fuel Gas Code (NFPA 54/ANSI-Z223.1).
NOTE − In the U.S. ue sizing must conform to the methods outlined in the
current National Fuel Gas Code (NFPA 54/ANSI-Z223.1) or applicable
provisions of local building codes.
1 Left side requires 4 in. if single wall vent is used on 14-1/2 in. “A” width
cabinets, 2 in. on 17-1/2 in. “B” width cabinets.
2 Clearance for installation on combustible oor if Optional Downow
Combustible Flooring Base is installed between furnace and combustible oor.
Not required in add-on cooling applications if installed in accordance with local
codes, National Fuel Gas Code ANSI-Z223.1 or National Standard of Canada
CAN/CSA-B149.1 and CAN/CSA-B149.2 Installation Code for Gas Burning
Appliances”. Do not install the furnace directly on carpeting, tile, or other
combustible materials other than wood ooring.
Sides 0 in. (0 mm) 1in. (0 mm)
Rear 0 in. (0 mm) 0 in. (0 mm)
Top 1 in. (25 mm) 1 in. (25 mm)
Front 2-1/4 in. (57 mm) 2-1/4 in. (57 mm)
Front (service/alcove) 24 in. (610 mm) 24 in. (610 mm)
Floor 2 Combustible 2 Combustible
Flue 1 in. (25 mm) 6 in. (152 mm)

Page 4
BLOWER DATA
ML180DF045P36A PERFORMANCE (Less Filter)
External
Static
Pressure
in. w.g.
Air Volume / Watts at Various Blower Speeds
High Medium-
High
Medium-
Low Low
cfm Watts cfm Watts cfm Watts cfm Watts
0.10 1524 567 1385 528 1144 431 947 366
0.20 1465 542 1351 490 1129 407 943 354
0.30 1414 517 1293 463 1111 393 950 341
0.40 1343 489 1236 436 1083 371 945 329
0.50 1255 464 1190 409 1038 356 897 311
0.60 1205 443 1106 380 999 333 870 292
0.70 1140 421 1059 366 943 317 816 275
0.80 1031 388 962 335 870 297 739 252
ML180DF070P36A PERFORMANCE (Less Filter)
External
Static
Pressure
in. w.g.
Air Volume / Watts at Various Blower Speeds
High Medium-
High
Medium-
Low Low
cfm Watts cfm Watts cfm Watts cfm Watts
0.10 1562 591 1386 539 1159 436 956 374
0.20 1506 553 1355 504 1149 418 953 361
0.30 1459 528 1314 473 1119 392 941 343
0.40 1390 500 1264 442 1082 374 915 323
0.50 1306 477 1200 415 1048 352 904 305
0.60 1213 441 1129 391 987 332 849 288
0.70 1140 417 1066 361 901 304 798 270
0.80 1038 395 975 342 836 283 717 244
ML180DF090P48B PERFORMANCE (Less Filter)
External
Static
Pressure
in. w.g.
Air Volume / Watts at Various Blower Speeds
High Medium-
High
Medium-
Low Low
cfm Watts cfm Watts cfm Watts cfm Watts
0.10 1929 755 1794 668 1585 572 1332 489
0.20 1864 717 1745 623 1544 540 1321 463
0.30 1779 683 1676 588 1496 510 1296 440
0.40 1694 647 1600 558 1443 473 1265 417
0.50 1596 607 1502 511 1363 440 1212 393
0.60 1483 577 1413 485 1258 406 1148 370
0.70 1340 544 1273 449 1148 374 1042 339
0.80 1221 505 1138 416 1018 350 917 307
ML180DF110P60C PERFORMANCE (Less Filter)
External
Static
Pressure
in. w.g.
Air Volume / Watts at Various Blower Speeds
High Medium-
High
Medium-
Low Low
cfm Watts cfm Watts cfm Watts cfm Watts
0.10 2760 1401 2325 1045 1888 871 1531 686
0.20 2670 1362 2319 1003 1937 847 1565 679
0.30 2557 1292 2257 964 1945 832 1605 674
0.40 2536 1287 2220 949 1935 812 1622 661
0.50 2384 1230 2152 911 1918 782 1626 644
0.60 2273 1191 2063 884 1884 762 1617 630
0.70 2197 1151 2021 875 1822 737 1574 610
0.80 2115 1140 1950 854 1749 708 1517 579
ML180DF045P24A PERFORMANCE (Less Filter)
External
Static
Pressure
in. w.g.
Air Volume / Watts at Various Blower Speeds
High Medium-
High
Medium-
Low Low
cfm Watts cfm Watts cfm Watts cfm Watts
0.10 1157 399 938 333 764 273 699 243
0.20 1120 381 924 322 745 264 677 237
0.30 1084 362 890 311 723 258 650 230
0.40 1027 349 864 298 695 250 633 224
0.50 975 334 814 283 674 238 605 215
0.60 902 322 764 268 623 225 564 203
0.70 831 305 682 248 549 208 477 186
0.80 713 280 576 228 470 192 401 171
ML180DF090P36B PERFORMANCE (Less Filter)
External
Static
Pressure
in. w.g.
Air Volume / Watts at Various Blower Speeds
High Medium-
High
Medium-
Low Low
cfm Watts cfm Watts cfm Watts cfm Watts
0.10 1695 647 1431 546 1180 468 973 379
0.20 1641 611 1405 516 1162 443 967 368
0.30 1595 589 1384 492 1146 420 958 349
0.40 1525 548 1344 472 1136 399 954 337
0.50 1438 515 1271 432 1110 374 929 319
0.60 1370 489 1197 400 1057 352 886 299
0.70 1260 451 1119 374 983 328 823 273
0.80 1164 425 1020 344 900 300 743 249

Page 5
ML180DF PARTS ARRANGEMENT
FIGURE 1
Primary Limit
(under combustion
air inducer)
Control Box
(includes integrated control,
interlock switch and transformer)
Gas Valve Burner Box
(includes sensor, ignitor
and rollout switches)
Combustion
Air Inducer
Blower Access Panel
Heating Compartment
Access Panel
Heat Exchanger
Flue Chase
Blower Assembly
Secondary Limit

Page 6
I-UNIT COMPONENTS
ML180DF unit components are shown in figure 1.The gas
valve, combustion air inducer and burners can be ac
cessed by removing the heating compartment access pan
el. Electrical components are in the control box (figure 2)
found in the blower section.
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.
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 ML180DF
Integrated Control
Transformer
Door
Interlock
Switch
3. Integrated 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 and 2), flame sensor and ignitor (figure 6).
The integrated control and ignitor work in combination to
ensure furnace ignition and ignitor durability. The inte
grated control, controls all major furnace operations. The
integrated control also features a RED LED for trouble
shooting and two accessory terminals rated at (1) one
amp. See table 3 for troubleshooting diagnostic codes.
The 120 volt ignitor is made from a high strength, silicon
nitride material that provides long life and trouble free
maintenance.
Electronic Ignition (Figure 4)
On a call for heat the integrated control monitors the com
bustion air inducer pressure switch. The control will not be
gin 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 after which the gas valve opens for a 4-sec
ond trial for ignition. The ignitor remains energized for the
first 3 seconds of trial for ignition. If ignition is not proved
during the trial for ignition, the integrated control will try four
more times with an inter purge and warm-up time between
trials of 30 seconds. After a total of five trials for ignition (in
cluding the initial trial), the integrated control goes into
Watchguard-Flame Failure mode. After a 60-minute reset
period, the integrated control will begin the ignition se
quence again.

Page 7
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
2 Sensor
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
FIGURE 3
INTEGRATED CONTROL
(Automatic Hot Surface Ignition System)
TERMINAL DESIGNATIONS
HUM
LINE
XFMR
EAC
COOL
HEAT
PARK
CONT
NEUTRALS
Humidifier (120VAC)
Input (120VAC)
Transformer (120VAC)
Indoor Air Qality Accessory Air Cleaner (120VAC)
Blower - Cooling Speed (120VAC)
Blower - Heating Speed (120VAC)
Dead terminals to park alternate spd taps
Continuous blower
Neutral terminals (120VAC)
PUSH BUTTON
LED
TWIN
TWIN Twinning Terminal (24VAC)
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉ
DEMAND
CAI
GAS VALVE
15
ON
OFF
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉ
ÉÉ
39
ÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉ
IGNITOR
35
1
Pre -Purge Ignitor Warm-up Trial for
Ignition Post
Purge
5 SEC69
*Blower on time will be 30 seconds after flame is sensed. Blower off time will depend on “OFF TIME” Setting.
INDOOR BLOWER
ÉÉÉÉÉÉÉÉÉ
Blower “On”*
Delay
ELECTRONIC IGNITION
FIGURE 4

Page 8
TABLE 3
Note - This control is equipped with a push button switch for
diagnostic code recall. The control stores the last 5 fault
codes in non-volatile memory. The most recent fault code is
flashed first, the oldest fault code is flashed last. There is a
2 second pause between codes. When the push button
switch is pressed for less than 5 seconds, the control will
flash the stored fault codes when the switch is released.
The fault code history may be cleared by pressing the push
button switch for more than 5 seconds.
Integrated Control Diagnostic Codes
DIAGNOSTIC CODES
LED Status DESCRIPTION
LED Off No power to control or control harware
fault detected.
LED On Normal operation.
1 Flash Flame present with gas vavle
de-energized.
2 Flashes Pressure switch closed with combustion
air inducer de-energized.
3 Flashes Pressure switch open with combus
tion air inducer energized.
4 Flashes Primary limit switch open.
5 Flashes Rollout switch open.
6 Flashes Pressure switch cycle lockout.
7 Flashes Lockout, burners fail to light.
8 Flashes Lockout, buners lost flame too many
times.
9 Flashes Line voltage polarity incorrect.
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 120 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 5.
Cooling Fan On Time
The fan on time is 2 seconds and is not adjustable.
Cooling Fan Off Time
The control has a 60 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 5
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

Page 9
ML180DF HEATING COMPONENTS
FIGURE 6
Internal flue pipe
Gasket
Orifice plate
Pressure switch
Collector box
Combustion air inducer
Ignitor
Sensor
Rollout
switch
Burners
Burner box
assembly
Manifold and
Gas valve
4. Flame Rollout Switch (Figure 6)
Flame rollout switch (S47) is a high temperature limit. The
limit is a N.C. SPST manual‐reset limit connected in series
with the integrated control A92. When S47 senses rollout,
the integrated control immediately stops ignition and
closes the gas valve. If unit is running and flame rollout is
detected, the gas valve will close and integrated control will
be disabled. Rollout can be caused by a blocked heat ex
changer, blocked flue or lack of combustion air. The switch
has a factory setpoint of 210°F and cannot be adjusted. To
manually reset a tripped switch, push the reset button located
on the control.
5. Primary Limit Control
The primary limit on ML180DF units is located in the heating
vestibule panel under the combustion air inducer. When ex
cess heat is sensed in the heat exchanger, the limit will open. If
the limit is open, the integrated control energizes the supply air
blower and closes the gas valve. The limit automatically resets
when unit temperature returns to normal. The switch must re
set within three minutes or the control will go into Watchguard
for one hour. The switch is factory set and cannot be ad
justed. The switch may have a different setpoint for each unit
model number. If limit switch must be replaced, refer to Len
nox ProductZone repair parts list on Lennox DaveNet®.
6. Flame Sensor (Figure 6)
A flame sensor is located on the left side of the burner sup
port. 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 (clean us
ing steel wool) without removing any part of the burners.
During operation, flame is sensed by current passed
through the flame and sensing electrode. The integrated
control allows the gas valve to remain open as long as
flame signal is sensed.
A microamp DC meter is needed to check the flame signal
on the integrated control.
Flame (microamp) signal is an electrical current which passes
from the integrated control to the sensor during unit operation.
Current passes from the sensor through the flame to ground to
complete a safety circuit.

Page 10
To Measure Flame Signal - Integrated Control:
Use a digital readout meter capable of reading DC micro
amps. See figure 7 and table 4 for flame signal check.
1 - Set the meter to the DC amps scale.
2 - Turn off supply voltage to control.
3 - Remove sensor wire from integrated control.
4 - Connect (-) lead to flame sensor wire.
5 - Connect (+) lead to Terminal FS on integrated control.
6 - Turn supply voltage on and close thermostat contacts to
cycle system.
7 - When main burners are in operation for two minutes, take
reading.
TABLE 4
Flame Signal in Microamps
Normal Low Drop Out
1.5 0.5 - 1.4 0.4
FIGURE 7
Measuring Flame Signal
(upflow furnace shown)
Flame
Sensor
Flame Sensor
Wire
Integrated
Control
Remove Sensor Wire from
Integrated Control and
Connect Alligator Clip (−)
to Flame Sensor Lead
Flame Sensor
Terminal
Remove Sensor Wire from
Integrated Control and
Connect Alligator Clip (+)
to Terminal on Control
(+)
DIGITAL METER
(+) To Control
Sensor
Terminal
(-) To
flame
sensor
Set dial to measure dc microamps
(+)
Red Collar
Indicates
Positive Lead

Page 11
7. Ignitor (Figure 6)
The nitride ignitor used on ML180DF units is made from a
proprietary ceramic material. To check ignitor, measure its
resistance and voltage. A value of 39 to 70 ohms indicates
a good ignitor. Voltage to the ignitor should be 120VAC.
See figure 8 for resistance, and voltage check.
NOTE - The ML180DF furnace contains electronic
components that are polarity sensitive. Make sure that
the furnace is wired correctly and is properly grounded.
FIGURE 8
Test 1
Check ignitor circuit for correct resistance.
Remove 4-pin plug from control.
Check ohms reading across terminals 2 and 4.
If value is correct (39 to 70 ohms), 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 2 and 4 (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.
Integrated Control Board
Detail
Test 1
Integrated Control Board
Detail
Test 2
Integrated Control Board
Detail
Test 3

Page 12
8. Gas Valve (Figure 6)
The ML180DF uses internally redundant gas valve to as
sure safety shut-off. If the gas valve must be replaced, the
same type valve must be used.
24VAC terminals and valve switch are located on the valve. All
terminals on the gas valve are connected to wires from the in
tegrated control. 24V applied to the terminals 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 spring.
9. Combustion Air Inducer (B6)
All ML180DF units use a combustion air inducer to move air
through the burners and heat exchanger during heating op
eration. The blower uses a 120VAC motor. The motor oper
ates during all heating operation and is controlled by inte
grated 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 pressure switch mounted on the combustion air inducer ori
fice plate is used to prove inducer operation. The combustion
air inducer orifice will be different for each model. See table 5
for orifice sizes. The switch monitors air pressure in the induc
er housing. During normal operation, the pressure in the
housing is negative. If pressure becomes less negative (sig
nifying any obstruction in the flue) the pressure switch opens.
When the proving switch opens, the integrated control (A92)
immediately de-energizes the gas valve to prevent burner
operation.
TABLE 5
ML180DF Unit C.A.I. Orifice Size
045P24A 1.094
045P36A 1.063
070(X)P36A 1.344
090P36B 1.531
090(X)P48B 1.531
110(X)P60C 1.718
10. Combustion Air Inducer
Pressure Switch (S18)
ML180DF series units are equipped with a combustion air
pressure switch located on the combustion air inducer ori
fice bracket. The switch is connected to the combustion air
inducer housing by means of a flexible silicone hose. It mon
itors negative air pressure in the combustion air inducer
housing.
The switch is a SPST Normally open proving switch electri
cally 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 integrated con
trol when pressure inside the combustion air inducer de
creases to a certain set point. Set points vary depending on
unit size. See table 6. 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 in
tegrated control and gas valve. A bleed port on the switch
allows relatively dry air in the vestibule to purge switch tub
ing, to prevent condensate build up.
TABLE 6
ML180DF Set Point inches w.c.
045P24A 0.60
045P36A 0.60
070(X)P36A 0.65
090P36B 0.60
090(X)P48B 0.60
110(X)P60C 0.65
110P60C 0.69
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
integrated control will not initiate ignition at start up.
Troubleshooting
See figure 9 for measuring operating pressure and check
ing resistance in the pressure switch.

Page 13
FIGURE 9
MULTI−METER
SET TO MEASURE OHMS
To
Pressure Switch
High
Low
or
Remove tubing from CAI and
insert “Tee” and additional tubing.
Field Provided
Tubing To CAI Port
11. Blower Motors and Capacitors
All ML180DF units use direct drive blower motors. All motors
are 120V permanent split capacitor motors to ensure maxi
mum efficiency. See Specifications section at the front of this
manual for motor specifications. Ratings for capacitors will
be on motor nameplate.
12. Secondary Limit Control
The secondary limit is located in the blower compartment on
the back side of the blower housing. See figure 10. When ex
cess heat is sensed in the blower compartment, the limit will
open. If the limit is open, the furnace control energizes the sup
ply air blower and closes the gas valve. The limit automatically
resets when unit temperature returns to normal. The secon
dary limit cannot be adjusted. FIGURE 10
To Remove Blower From Unit:
1. Disconnect Power, 2. Remove internal flue pipe and chase
3. Remove Control Box 4. Remove Bolts. 5. Unplug Motor
Wires From Control Board. Then Slide Out Front of Unit.
Supply Air Blower

Page 14
II- PLACEMENT AND INSTALLATION
Make sure unit is installed in accordance with installation
instructions and applicable codes.
III- START‐UP
A- Heating Start‐Up
WARNING
Shock and burn hazard.
ML180DF units are equipped with a hot surface igni
tion system. Do not attempt to light manually.
Gas Valve Operation
FIGURE 11
GAS VALVE SHOWN IN ON POSITION
MANIFOLD
PRESSURE
OUTLET
PORT
INLET
PRESSURE
PORT
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
1 - STOP! Read the safety information at the beginning of
this section.
2 - Set the thermostat to the lowest setting.
3 - Turn off all electrical power to the unit.
4 - This furnace is equipped with an ignition device which
automatically lights the burners. Do not try to light the
burners by hand.
5 - Remove the heating compartment access panel.
6 - Move gas valve switch to OFF position. Do not
force. See figure 11.
7 - Wait five minutes to clear out any gas. If you then smell
gas, STOP! Immediately call your gas supplier from a
neighbor's phone. Follow the gas supplier's instruc
tions. If you do not smell gas go to next step.
8 - Move gas valve switch to ON position. Do not force.
See figure 11.
9 - Replace the heating compartment access panel.
10- Turn on all electrical power to to the unit.
11- Set the thermostat to desired setting.
NOTE - When unit is initially started, steps 1 through 11
may need to be repeated to purge air from gas line.
12- If the appliance will not operate, follow the instructions
“Turning Off Gas to Unit” and call the gas supplier.
Turning Off Gas to Unit
1 - Set the thermostat to the lowest setting.
2 - Turn off all electrical power to the unit if service is to be
performed.
3 - Remove the heating compartment access panel.
4 - Move gas valve switch to OFF position. Do not
force. See figure 11.
5 - Replace the heating compartment access panel.
B- Safety or Emergency Shutdown
Disconnect main power to unit. Close manual and main gas
valves.
C- 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 leaks into combustion chamber. Turn off power
to unit. All access panels and covers must be in place and
secured.
IV-HEATING SYSTEM SERVICE CHECKS
A- C.S.A. Certification
All units are C.S.A. design certified without modifications.
Refer to the ML180DF 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 at
taching 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 0.5 psig (14” W.C.). See figure 12. If
the pressure is equal to or greater than 0.5 psig (14”W.C.),
close the manual shut-off valve before pressure testing to
isolate furnace from gas supply.

Page 15
FIGURE 12
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- Gas Pressure Adjustment
Gas Flow (Approximate)
TABLE 7
GAS METER CLOCKING CHART
ML180DF
Unit
Seconds for One Revolution
Natural LP
1 cu ft
Dial
2 cu ft
Dial
1 cu ft
Dial
2 cu ft
DIAL
-045 80 160 200 400
-070 55 110 136 272
-090 41 82 102 204
-110 33 66 82 164
-135 27 54 68 136
Natural-1000 btu/cu ft LP-2500 btu/cu ft
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 7. If manifold pressure matches table 9 and rate is
incorrect, check gas orifices for proper size and restric
tion. Remove temporary gas meter if installed.
NOTE - To obtain accurate reading, shut off all other gas
appliances connected to meter.
E- Supply and Manifold Pressure
Supply Pressure Measurement
1 - Remove the threaded plug from the inlet side of the
gas valve and install a field-provided barbed fitting.
Connect to a test gauge to measure supply pressure.
2 - Start unit and allow 5 minutes for unit to reach steady
state.
3 - After allowing unit to stabilize for 5 minutes, record
supply pressure and compare to value given in table 9.
Manifold Pressure Measurement
1 - Remove the threaded plug from the outlet side of the
gas valve and install a field-provided barbed fitting.
Connect to a test gauge to measure manifold pres
sure.
2 - Start unit and allow 5 minutes for unit to reach steady
state.
3 - While waiting for the unit to stabilize, observe the
flame. Flame should be stable and should not lift from
burner. Natural gas should burn blue.
4 - After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to value given in table
9.
NOTE - Shut unit off and remove manometer as soon as an
accurate reading has been obtained. Take care to remove
barbed fitting and replace threaded plug.
F- Proper Combustion
Furnace should operate a minimum 15 minutes with cor
rect manifold pressure and gas flow rate before checking
combustion. Take combustion sample beyond the flue out
let and compare to the tables below. The maximum carbon
monoxide reading should not exceed 50 ppm.
TABLE 8
ML180DF Unit CO2%For
Nat
CO2% For
L.P.
-045
6.0 - 7.5 6.9 - 8.5
-070
-090
-110
G- High Altitude
The manifold pressure may require adjustment and com
bustion air pressure switch may need replacing to ensure
proper combustion at higher altitudes. Refer to table 9 for
manifold pressure and table 10 for pressure switch change
and gas conversion kits.
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.

Page 16
TABLE 9
Manifold Pressure Settings at all Altitudes
Model
Input Size Gas 0-4500 ft 4501-7500 ft 7501 - 10,000 ft
Supply Pressure
in.wg.
Min Max
045 Nat 3.5 3.5 3.5 4.5 13.0
LP/propane 10.0 10.0 10.0 11.0 13.0
070 Nat 3.5 3.3 3.5 4.5 13.0
LP/propane 10.0 10.0 10.0 11.0 13.0
090 Nat 3.5 3.3 3.5 4.5 13.0
LP/propane 10.0 10.0 10.0 11.0 13.0
110 Nat 3.5 3.3 3.5 4.5 13.0
LP/propane 10.0 10.0 10.0 11.0 13.0
TABLE 10
Pressure Switch and Gas Conversion Kits at all Altitudes
Model
Input Size
High Altitude Pressure Switch Kit
High Altitude
Natural Gas Burner
Orifice Kit
Natural Gas to LP/Propane
Gas Change Over Kit
LP/Propane to
Natural Gas
Change Over Kit
0-4500 ft 4501-7500 ft 7501 - 10,000 ft 7501 - 10,000 ft 0 - 7500 ft 7501 - 10,000 ft 0 - 7500 ft
045
No Change
No Change
80W51 73W37 70W89 76W15 73W81
070 80W52
090 No Change
090(X) 80W52
110
NOTE - A natural to L.P. propane gas changeover kit is necessary to convert this unit. Refer to the changeover kit installation instruction for the conversion
procedure.

Page 17
H- Proper Ground and Voltage
A poorly grounded furnace can contribute to premature ig
nitor failure. Use the following procedure to check for
ground and voltage to the integrated control.
1 - Measure the AC voltage between Line Neutral (spade
terminals) and “C” terminal (low voltage terminal
block) on the integrated control. See figure 13. A wide
variation in the voltage between Line Neutral and “C”
as a function of load indicates a poor or partial ground.
Compare the readings to the table below. If the read
ings exceed the maximum shown in table 1, make re
pairs before operating the furnace.
2 - In addition, measure the AC voltage from Line Hot to
Line Neutral (spade terminals) on the integrated con
trol. See figure 14. This voltage should be in the range
of 97 to 132 Vac
TABLE 11
Furnace Status Measurement VAC
Expected Maximum
Power On Furnace Idle 0.3 2
CAI / Ignitor Energized 0.75 5
Indoor Blower Energized Less than 2 10
CHECK VOLTAGE BETWEEN LINE NEUTRAL
AND LOW VOLTAGE “C” TERMINAL
FIGURE 13
CHECK VOLTAGE BETWEEN LINE HOT
AND LINE NEUTRAL
FIGURE 14

Page 18
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.
B-Temperature Rise (Figure 15)
Temperature rise for ML180DF units depends on unit input,
blower speed, blower horsepower and static pressure as
marked on the unit rating plate. The blower speed must be
set for unit operation within the range of “TEMP. RISE °F”
listed on the unit rating plate.
FIGURE 15
Upflow Furnace Shown
Supply Air
Return Air
TEMPERATURE RISE
Supply Duct Temperature _____
Return Duct Temperature - ____
Temperature Rise = _________
C-External Static Pressure
1 - Tap locations shown in figure 16 .
2 - Punch a 1/4” diameter hole in supply and return air ple
nums. Insert manometer hose flush with inside edge of
hole or insulation. Seal around the hose with perma
gum. Connect the zero end of the manometer to the
discharge (supply) side of the system. On ducted sys
tems, connect the other end of manometer to the return
duct as above.
3 - With only the blower motor running and the evaporator
coil dry, observe the manometer reading. Adjust blow
er motor speed to deliver the air desired according to
the job requirements. For heating speed external static
pressure drop must not be more than 0.5” W.C. For
cooling speed external static pressure drop must not
be more than 0.8” W.C.
4 - Seal the hole when the check is complete.
FIGURE 16
Upflow Furnace Shown
EXTERNAL STATIC PRESSURE
Supply Duct Static
Return Duct Static +
Total Duct Static =
(dry coil)
Supply Air
Return Air -
+
or
High
Low
D-Blower Speed Taps
Blower speed tap changes are made on the integrated con
trol. See figure 3. The heating tap is connected to the
“HEAT” terminal and the cooling tap is connected to the
“COOL” terminal. The continuous blower tap is connected
to the “CONT” terminal. Unused taps must be secured on
dummy terminals labeled ”PARK. To change out existing
speed tap, turn off power and switch out speed tap with tap
connected to “PARK”. See blower speed tap table on unit
diagram for motor tap colors for each speed.

Page 19
VI-MAINTENANCE
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.
At the beginning of each heating season, the system
should be checked as follows:
B-Filters
Filters should be inspected monthly. Clean or replace the
filters when necessary to ensure that the furnace operates
properly. Replacement filters must be rated for high veloc
ity airflow. See table 12.
IMPORTANT
If a highefficiency filter is being installed as part of
this system to ensure better indoor air quality, the fil
ter must be properly sized. Highefficiency filters
have a higher static pressure drop than standardef
ficiency glass/foam filters. If the pressure drop is too
great, system capacity and performance may be re
duced. The pressure drop may also cause the limit to
trip more frequently during the winter and the indoor
coil to freeze in the summer, resulting in an increase
in the number of service calls.
Before using any filter with this system, check the
specifications provided by the filter manufacturer
against the data given in the appropriate Lennox
Product Specifications bulletin. Additional informa
tion is provided in Service and Application Note
ACC002 (August 2000).
TABLE 12
Cabinet Width Return Air Filter Size (inches)
A (14-1/2”) 14 x 25 x 1 (1)
B (17-1/2”) 16 x 25 x 1 (1)
C (21”) 20 x 25 x 1 (1)
Cleaning the Heat Exchanger and Burners
NOTE - Use papers or protective covering in front of the fur
nace during cleaning.
1 - Turn off both electrical and gas power supplies to fur
nace.
2 - Remove flue pipe, top cap, flue chase and internal flue
pipe assembly from the unit.
3 - Label the wires from gas valve, rollout switches, prima
ry limit switch and make-up box then disconnect them.
4 - Remove the screws that secure the combustion air in
ducer/pressure switch assembly to the collector box.
Carefully remove the combustion air inducer to avoid
damaging blower gasket. If gasket is damaged, it must
be replaced to prevent leakage.
5 - Remove the collector box located behind the combus
tion air inducer. Be careful with the collector box gas
ket. If the gasket is damaged, it must be replaced to
prevent leakage.
6 - Disconnect gas supply piping. Remove the four screws
securing the burner manifold assembly to the vestibule
panel and remove the assembly from the unit.
7 - NOX units only - Remove screw securing NOX insert.
Remove NOX insert.
8 - Remove screws from both sides, top and bottom of
vestibule panel.
9 - Remove heat exchanger. It may be necessary to
spread cabinet side to allow more room. If so, remove
five screws from the left side or right side of cabinet.
See figure 18.
10- Back wash using steam. Begin from the burner opening
on each clam. Steam must not exceed 275°F.
11- To clean burners, run a vacuum cleaner with a soft brush
attachment over the face of burners. Visually inspect in
side the burners and crossovers for any blockage
caused by foreign matter. Remove any blockage. Figure
17 shows burner detail.
12- To clean the combustion air inducer visually inspect and
using a wire brush clean where necessary. Use com
pressed air to clean off debris and any rust.
13- Reinstall heat exchanger in vestibule. (Replace the
five screws in the cabinet from step 10 if removed).
14- NOX units only - replace NOX inserst.
15- Reinstall collector box, combustion air assembly, inter
nal flue pipe and flue chase. Seal with high tempera
ture RTV. Reinstall all screws to the collector box and
combustion air inducer. Failure to replace all screws
may cause leaks. Inspect gaskets for any damage and
replace if necessary.

Page 20
ML180DF BURNER, COMBUSTION AIR INDUCER ASSEMBLY &
HEAT EXCHANGER REMOVAL
FIGURE 17
Gasket
Internal flue pipe
Glue chase Gasket
Orifice plate
Pressure switch
Collector box Nox insert
(if applicable)
Heat exchanger
Combustion air inducer
Ignitor
Sensor
Rollout
switch
Burners
Burner box
assembly
Manifold and
Gas valve
Retention rings
Cross over
16- Reinstall burner box, manifold assembly and burner box
cover.
17- Reconnect all wires.
18- Reconnect top cap and vent pipe to combustion air in
ducer outlet.
19- Reconnect gas supply piping.
20- Turn on power and gas supply to unit.
21- Set thermostat and check for proper operation.
22- Check all piping connections, factory and field, for gas
leaks. Use a leak detecting solution or other preferred
means.
CAUTION
Some soaps used for leak detection are corrosive to
certain metals. Carefully rinse piping thoroughly af
ter leak test has been completed. Do not use
matches, candles, flame or other sources of ignition
to check for gas leaks.
23- If a leak is detected, shut gas and electricity off and
repair leak.
24- Repeat steps 22 and 23 until no leaks are detected.
25- Replace access panel. FIGURE 18
Remove five screws if necessary
(either side of cabinet)
1
2
3
4
5