ml180df(x) - HVACPartsShop

Corp. 1219-L4
Revised 02/2013
Service Literature
ML180DF(X)
ML180DF series units are mid-efficiency gas furnaces
used for downflow applications only, manufactured with
Lennox Duralokt heat 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
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.
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
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.
V Typical Operating Characteristics . . . . . . . . . Page 19
VI Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . Page 19
VII Wiring and Sequence of Operation . . . . . . Page 22
VIII Twinning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 27
Page 1
WARNING
Sharp edges.
Be careful when servicing unit to avoid sharp edges
which may result in personal injury.
© 2013 Lennox Industries Inc.
SPECIFICATIONS
Gas
Heating
Performance
Model No.
Model No. - Low NOx
80%
80%
80%
44,000
66,000
Output - Btuh
35,000
36,000
53,000
Temperature rise range - °F
High Static - in. w.g.
Flue connection - in. round
Gas pipe size IPS
Indoor
Blower
Wheel nom. dia. x width - in.
Motor output - hp
Electrical
Data
ML180DF070P36A
ML180DF070XP36A
44,000
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
Connections
in.
ML180DF045P36A
---
Input - Btuh
1
AFUE
ML180DF045P24A
---
25 - 55
15 - 45
25 - 55
3.5 / 10.0
3.5 / 10.0
3.5 / 10.0
0.50
0.50
0.50
4
4
4
1/2
1/2
1/2
10 x 7
10 x 8
10 x 8
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
Voltage
120 volts - 60 hertz - 1 phase
Blower motor full load amps
3.1
6.1
6.1
Maximum overcurrent protection
15
15
15
105
113
128
Shipping Data
lbs. - 1 package
NOTE - Filters and provisions for mounting are not furnished and must be field provided.
1
Annual Fuel Utilization Efficiency 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
1
AFUE
Input - Btuh
80%
80%
80%
88,000
88,000
110,000
71,000
71,000
89,000
35 - 65
25 - 55
30 - 60
3.5 / 10.0
3.5 / 10.0
3.5 / 10.0
0.50
0.50
0.50
4
4
4
Flue connection - in. round
Gas pipe size IPS
Wheel nom. dia. x width - in.
Motor output - hp
Electrical
Data
ML180DF110P60C
ML180DF110XP60C
Output - Btuh
High Static - in. w.g.
Indoor
Blower
ML180DF090P48B
ML180DF090XP48B
Temperature rise range - °F
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
Connections
in.
ML180DF090P36B
---
1/2
1/2
1/2
10 x 9
10 x 10
11-1/2 x 10
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
Voltage
120 volts - 60 hertz - 1 phase
Blower motor full load amps
6.1
8.2
10.0
Maximum overcurrent protection
15
15
15
131
140
160
Shipping Data
lbs. - 1 package
NOTE - Filters and provisions for mounting are not furnished and must be field provided.
1
Annual Fuel Utilization Efficiency based on DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherized furnaces.
Page 2
OPTIONAL ACCESSORIES - ORDER SEPARATELY
“A” Width
Models
“B” Width
Models
“C” Width
Models
11M59
11M60
11M61
15L38
15L38
15L38
51W06
51W07
51W08
(1) 20 x 20 x 1
(2) 20 x 16 x 1
(2) 20 x 16 x 1
Night Service Kit
51W03
51W03
51W03
Universal Service Kit - Switches
89W19
89W19
89W19
CABINET ACCESSORIES
Downflow Combustible Flooring Base
CONTROLS
Twinning Kit
FILTERS
1
Downflow Filter Cabinet
No. and Size of filter - in.
service kits
1
Cleanable polyurethane, frame-type filter.
GAS HEAT ACCESSORIES
High Altitude
Pressure Switch Kit
Input
0 - 4500 ft.
Natural Gas
LPG/Propane
High Altitude
to Natural Gas Kit
Orifice Kit
Natural Gas to
LPG/Propane Kit
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
HIGH ALTITUDE DERATE
NOTE - Units may be installed at altitudes up to 4500 ft. above sea level without any modifications.
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.
Gas Manifold Pressure (Outlet) in. w.g.
0 - 4500 Feet
Input
1
4501 - 7500 Feet
Line Pressure - in. w.g.
7501 - 10,000 ft.
Minimum
Maximum
Natural
Gas
LPG/
Propane
Natural
Gas
LPG/
Propane
10
3.5
10
4.5
11
13
3.3
10
3.5
10
4.5
11
13
10
3.3
10
3.5
10
4.5
11
13
10
3.3
10
3.5
10
4.5
11
13
Natural
Gas
LPG/
Propane
Natural
Gas
LPG/
Propane
045
3.5
10
3.5
070
3.5
10
090
3.5
110
3.5
1
Natural Gas High Alitude Orifice Kit required.
INSTALLATION CLEARANCES
Vent Type
Type B1
Type C
Sides
0 in. (0 mm)
1
Rear
0 in. (0 mm)
0 in. (0 mm)
Top
1 in. (25 mm)
1 in. (25 mm)
2-1/4 in. (57 mm)
2-1/4 in. (57 mm)
24 in. (610 mm)
24 in. (610 mm)
Front
Front (service/alcove)
Floor
Flue
2
Combustible
1 in. (25 mm)
2
in. (0 mm)
Combustible
6 in. (152 mm)
Page 3
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. flue 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 floor if Optional Downflow
Combustible Flooring Base is installed between furnace and combustible floor.
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 flooring.
BLOWER DATA
ML180DF045P24A PERFORMANCE (Less Filter)
Air Volume / Watts at Various Blower Speeds
External
MediumMediumStatic
High
Low
High
Low
Pressure
in. w.g. cfm Watts cfm Watts cfm Watts cfm Watts
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
1157
1120
1084
1027
975
902
831
713
399
381
362
349
334
322
305
280
938
924
890
864
814
764
682
576
333
322
311
298
283
268
248
228
764
745
723
695
674
623
549
470
273
264
258
250
238
225
208
192
699
677
650
633
605
564
477
401
243
237
230
224
215
203
186
171
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
ML180DF070P36A PERFORMANCE (Less Filter)
Air Volume / Watts at Various Blower Speeds
External
MediumMediumStatic
High
Low
High
Low
Pressure
in. w.g. cfm Watts cfm Watts cfm Watts cfm Watts
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
1562
1506
1459
1390
1306
1213
1140
1038
591
553
528
500
477
441
417
395
1386
1355
1314
1264
1200
1129
1066
975
539
504
473
442
415
391
361
342
1159
1149
1119
1082
1048
987
901
836
436
418
392
374
352
332
304
283
956
953
941
915
904
849
798
717
1929
1864
1779
1694
1596
1483
1340
1221
755
717
683
647
607
577
544
505
1794
1745
1676
1600
1502
1413
1273
1138
668
623
588
558
511
485
449
416
1585
1544
1496
1443
1363
1258
1148
1018
572
540
510
473
440
406
374
350
1332
1321
1296
1265
1212
1148
1042
917
1524
1465
1414
1343
1255
1205
1140
1031
567
542
517
489
464
443
421
388
1385
1351
1293
1236
1190
1106
1059
962
528
490
463
436
409
380
366
335
1144
1129
1111
1083
1038
999
943
870
431
407
393
371
356
333
317
297
947
943
950
945
897
870
816
739
366
354
341
329
311
292
275
252
ML180DF090P36B PERFORMANCE (Less Filter)
Air Volume / Watts at Various Blower Speeds
External
MediumMediumStatic
High
Low
High
Low
Pressure
in. w.g. cfm Watts cfm Watts cfm Watts cfm Watts
374
361
343
323
305
288
270
244
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
ML180DF090P48B PERFORMANCE (Less Filter)
Air Volume / Watts at Various Blower Speeds
External
MediumMediumStatic
High
Low
High
Low
Pressure
in. w.g. cfm Watts cfm Watts cfm Watts cfm Watts
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
ML180DF045P36A PERFORMANCE (Less Filter)
Air Volume / Watts at Various Blower Speeds
External
MediumMediumStatic
High
Low
High
Low
Pressure
in. w.g. cfm Watts cfm Watts cfm Watts cfm Watts
1695
1641
1595
1525
1438
1370
1260
1164
647
611
589
548
515
489
451
425
1431
1405
1384
1344
1271
1197
1119
1020
546
516
492
472
432
400
374
344
1180
1162
1146
1136
1110
1057
983
900
468
443
420
399
374
352
328
300
973
967
958
954
929
886
823
743
379
368
349
337
319
299
273
249
ML180DF110P60C PERFORMANCE (Less Filter)
Air Volume / Watts at Various Blower Speeds
External
MediumMediumStatic
High
Low
High
Low
Pressure
in. w.g. cfm Watts cfm Watts cfm Watts cfm Watts
489
463
440
417
393
370
339
307
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
Page 4
2760
2670
2557
2536
2384
2273
2197
2115
1401
1362
1292
1287
1230
1191
1151
1140
2325
2319
2257
2220
2152
2063
2021
1950
1045
1003
964
949
911
884
875
854
1888
1937
1945
1935
1918
1884
1822
1749
871
847
832
812
782
762
737
708
1531
1565
1605
1622
1626
1617
1574
1517
686
679
674
661
644
630
610
579
ML180DF PARTS ARRANGEMENT
Secondary Limit
Blower Assembly
Flue Chase
Control Box
(includes integrated control,
interlock switch and transformer)
Blower Access Panel
Heat Exchanger
Combustion
Air Inducer
Primary Limit
(under combustion
air inducer)
Gas Valve
Heating Compartment
Access Panel
Burner Box
(includes sensor, ignitor
and rollout switches)
FIGURE 1
Page 5
3. Integrated Control (A92)
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.
CONTROL BOX ML180DF
Integrated Control
Door
Interlock
Switch
Transformer
FIGURE 2
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 (bypassed). 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 6
TABLE 2
TABLE 1
4-Pin Terminal Designation
PIN #
FUNCTION
PIN #
12-Pin Terminal Designations
FUNCTION
1
Combustion Air Inducer Line
1
High Limit Output
2
3
4
Ignitor Line
2
Sensor
Combustion Air Inducer Neutral
3
24V Line
Ignitor Neutral
4
Not Used
5
Rollout Switch Out
6
24V Neutral
7
High Limit Input
8
Ground
9
Gas Valve Common
10
Pressure Switch In
11
Rollout Switch In
12
Gas Valve Out
INTEGRATED CONTROL
(Automatic Hot Surface Ignition System)
HUM
LINE
XFMR
EAC
COOL
HEAT
PARK
CONT
NEUTRALS
TWIN
TERMINAL DESIGNATIONS
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)
Twinning Terminal (24VAC)
LED
PUSH BUTTON
TWIN
FIGURE 3
ÉÉ
ÉÉ
ON
OFF
DEMAND
CAI
IGNITOR
GAS VALVE
INDOOR BLOWER
ELECTRONIC IGNITION
1
35
15
69
39
5 SEC
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉ
Pre -Purge
Ignitor Warm-up
Trial for
Ignition
Blower “On”*
Delay
Post
Purge
*Blower on time will be 30 seconds after flame is sensed. Blower off time will depend on “OFF TIME” Setting.
FIGURE 4
Page 7
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
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.
HEAT FAN‐OFF TIME IN SECONDS
NO JUMPER
To adjust fan-off timing, reposition jumper across pins to
achieve desired setting.
60 Second
off Time
60
90
120
180
LED Status
90 Second
off Time
120 Second
off Time
FIGURE 5
Page 8
180 Second
off Time
60
90
120
180
diagnostic code recall. The control stores the last 5 fault
60
90
120
180
Note - This control is equipped with a push button switch for
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.
60
90
120
180
TABLE 3
ML180DF HEATING COMPONENTS
Internal flue pipe
Gasket
Orifice plate
Pressure switch
Collector box
Burner box
assembly
Combustion air inducer
Ignitor
Sensor
Manifold and
Gas valve
Burners
Rollout
switch
FIGURE 6
6. Flame Sensor (Figure 6)
4. Flame Rollout Switch (Figure 6)
Flame rollout switch (S47) is a high temperature limit. The
A flame sensor is located on the left side of the burner sup­
limit is a N.C. SPST manual‐reset limit connected in series
port. The sensor is mounted on the flame rollout plate and
with the integrated control A92. When S47 senses rollout,
the tip protrudes into the flame envelope of the left-most
the integrated control immediately stops ignition and
burner. The sensor can be removed for service (clean us­
closes the gas valve. If unit is running and flame rollout is
ing steel wool) without removing any part of the burners.
detected, the gas valve will close and integrated control will
During operation, flame is sensed by current passed
be disabled. Rollout can be caused by a blocked heat ex­
through the flame and sensing electrode. The integrated
changer, blocked flue or lack of combustion air. The switch
control allows the gas valve to remain open as long as
has a factory setpoint of 210°F and cannot be adjusted. To
flame signal is sensed.
manually reset a tripped switch, push the reset button located
A microamp DC meter is needed to check the flame signal
on the control.
on the integrated control.
5. Primary Limit Control
Flame (microamp) signal is an electrical current which passes
The primary limit on ML180DF units is located in the heating
from the integrated control to the sensor during unit operation.
vestibule panel under the combustion air inducer. When ex­
Current passes from the sensor through the flame to ground to
complete a safety circuit.
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®.
Page 9
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
Low
Drop Out
0.5 - 1.4
1.5
0.4
Normal
Measuring Flame Signal
(upflow furnace shown)
Remove Sensor Wire from
Integrated Control and
Connect Alligator Clip (−)
to Flame Sensor Lead
Flame
Sensor
Flame Sensor
Wire
DIGITAL METER
Set dial to measure dc microamps
Integrated
Control
Red Collar
Indicates
Positive Lead
Flame Sensor
Terminal
(+)
(+) To Control
Sensor
Terminal
Remove Sensor Wire from
Integrated Control and
Connect Alligator Clip (+)
to Terminal on Control
FIGURE 7
Page 10
(+)
(-) To
flame
sensor
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.
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 1
Integrated Control Board
Detail
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 2
Integrated Control Board
Detail
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.
Test 3
Integrated Control Board
Detail
FIGURE 8
Page 11
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.
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
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
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 bypassed 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 12
Remove tubing from CAI and
insert “Tee” and additional tubing.
MULTI−METER
SET TO MEASURE OHMS
To
Pressure Switch
Field Provided
Tubing To CAI Port
High
or
Low
FIGURE 9
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.
Page 13
Supply Air Blower
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.
FIGURE 10
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
Disconnect main power to unit. Close manual and main gas
valves.
Shock and burn hazard.
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.
ML180DF units are equipped with a hot surface igni­
tion system. Do not attempt to light manually.
Gas Valve Operation
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
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
MANIFOLD
PRESSURE
OUTLET
PORT
IV-HEATING SYSTEM SERVICE CHECKS
INLET
PRESSURE
PORT
GAS VALVE SHOWN IN ON POSITION
FIGURE 11
1 - STOP! Read the safety information at the beginning of
this section.
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
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.
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.
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.
CAUTION
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 14
GAS PIPING TEST PROCEDURE
MANUAL MAIN SHUT-OFF VALVE
WILL NOT HOLD TEST PRESSURE
IN EXCESS OF 0.5 PSIG (14”W.C.)
CAP
GAS VALVE
FIELD PROVIDED
LINE PRESSURE TAP
FIGURE 12
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
Seconds for One Revolution
Natural
LP
ML180DF
Unit
1 cu ft
2 cu ft
1 cu ft
2 cu ft
Dial
Dial
Dial
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.
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
CO2% For
CO2% For
ML180DF Unit
-045
-070
-090
-110
Nat
L.P.
6.0 - 7.5
6.9 - 8.5
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.
NOTE - To obtain accurate reading, shut off all other gas
appliances connected to meter.
Page 15
IMPORTANT
For safety, shut unit off and remove manometer as
soon as an accurate reading has been obtained.
Take care to replace pressure tap plug.
TABLE 9
Manifold Pressure Settings at all Altitudes
Model
Input Size
045
070
090
110
Supply Pressure
in.wg.
Gas
0-4500 ft
4501-7500 ft
7501 - 10,000 ft
Min
Max
Nat
3.5
3.5
3.5
4.5
13.0
LP/propane
10.0
10.0
10.0
11.0
13.0
Nat
3.5
3.3
3.5
4.5
13.0
LP/propane
10.0
10.0
10.0
11.0
13.0
Nat
3.5
3.3
3.5
4.5
13.0
LP/propane
10.0
10.0
10.0
11.0
13.0
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
0-4500 ft
045
4501-7500 ft
80W52
090
No Change
110
Natural Gas to LP/Propane
Gas Change Over Kit
LP/Propane to
Natural Gas
Change Over Kit
7501 - 10,000 ft
7501 - 10,000 ft
0 - 7500 ft
7501 - 10,000 ft
0 - 7500 ft
80W51
73W37
70W89
76W15
73W81
No Change
070
090(X)
High Altitude
Natural Gas Burner
Orifice Kit
No Change
80W52
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 16
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
Power On Furnace Idle
CAI / Ignitor Energized
Indoor Blower Energized
CHECK VOLTAGE BETWEEN LINE HOT
AND LINE NEUTRAL
Measurement VAC
Expected
Maximum
0.3
2
0.75
5
Less than 2
10
CHECK VOLTAGE BETWEEN LINE NEUTRAL
AND LOW VOLTAGE “C” TERMINAL
FIGURE 14
FIGURE 13
Page 17
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.
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.
EXTERNAL STATIC PRESSURE
Supply Duct Static
Return Duct Static +
Total Duct Static =
(dry coil)
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.
Upflow Furnace Shown
Supply Air
TEMPERATURE RISE
Supply Duct Temperature _____
Return Duct Temperature - ____
Temperature Rise = _________
High
Upflow Furnace Shown
Low
Supply Air
or
Return Air
+
-
FIGURE 16
D-Blower Speed Taps
Return Air
FIGURE 15
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 18
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 high­efficiency filter is being installed as part of
this system to ensure better indoor air quality, the fil­
ter must be properly sized. High­efficiency filters
have a higher static pressure drop than standard­ef­
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
ACC­00­2 (August 2000).
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).
TABLE 12
14- NOX units only - replace NOX inserst.
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)
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 19
ML180DF BURNER, COMBUSTION AIR INDUCER ASSEMBLY &
HEAT EXCHANGER REMOVAL
Internal flue pipe
Gasket
Gasket
Glue chase
Orifice plate
Heat exchanger
Pressure switch
Collector box
Burner box
assembly
Nox insert
(if applicable)
Combustion air inducer
Ignitor
Burners
Sensor
Manifold and
Gas valve
Retention rings
Rollout
switch
Cross over
FIGURE 17
16- Reinstall burner box, manifold assembly and burner box
cover.
Remove five screws if necessary
(either side of cabinet)
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.
4
CAUTION
3
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.
5
2
23- If a leak is detected, shut gas and electricity off and
repair leak.
1
24- Repeat steps 22 and 23 until no leaks are detected.
FIGURE 18
25- Replace access panel.
Page 20
C-Supply Air Blower
1 - Check and clean blower wheel.
2 - Motors used on the Lennox ML180DF series units
are permanently lubricated and need no further lu­
brication.
D-Flue and Chimney
Flue must conform to local codes. In the absence of local
codes, flue must meet the National Fuel Gas Code
ANSI-Z223.1 venting requirements. Flue pipe deteriorates
from the inside out and must be disconnected in order to
check thoroughly. Check flue pipe, chimney and all con­
nections for tightness and to make sure there is no block­
age or leaks.
E-Electrical
Check Motor AMP Draw
(upflow furnace shown)
OFF
−P
EX
MR
W
3
2
1
kWh
kVAr
V1 V2 V3 COM
M
1 - Check all wiring for loose connections.
2 - Check for the correct voltage at the furnace (furnace
operating). Correct voltage is 120VAC + 10%
3 - Check amp-draw using a true RMS meter on the blow­
er motor with blower access panel in place. See figure
19.
Furnace Nameplate__________Actual__________
Page 21
True RMS Meter
FIGURE 19
VII- WIRING AND SEQUENCE OF OPERATION
ML180DF Schematic Wiring Diagram and Sequence of Operation
3
10
1
4
5
5
2
6
8
7
9
1
1-
Line voltage is applied to L1 and N. the T1 low voltage transformer is energized, and line voltage is applied to B3 indoor blower.
2-
S47 rollout switch must be closed in order for 24V from transformer to be output on integrated control ”R” to power thermostat.
3-
When there is a call for heat, W1 of the thermostat energizes W of the furnace control with 24VAC.
45-
A92 integrated control runs a self-check. S10 primary limit and S21 secondary limit contacts are found to be closed. Call for heat can continue.
A92 integrated control energizes B6 combustion air inducer. S18 combustion air pressure switch closes . Once S18 closes, a 15-second
pre-purge follows.
A92 integrated control energizes R33 ignitor. A 20-second warm-up period begins.
67-
GV1 gas valve opens for a 4-second trial for ignition
8-
Flame is sensed, gas valve remains open for the heat call.
9-
After 30-second delay (from flame sensed), A92 integrated control applies 24VAC to Heat speed of B3 indoor blower.
10 - When heat demand is satisfied, W1 of the indoor thermostat de-energizes W of A92ignition control which de-energizes GV1 gas valve.
B6 combustion air inducer continues a 5-second post-purge period, and B3 indoor blower completes a selected OFF time delay.
Page 22
Troubleshooting: Heating Sequence of Operation
HEATING SEQUENCE OF OPERATION
ABNORMAL HEATING MODE
NORMAL HEATING MODE
POWER ON
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER DELAY OFF.
LED: OFF
NO
CONTROL SELF-CHECK OKAY?
YES
NO
POLARITY REVERSED.
LED: 9 FLASHES
IS POLARITY CORRECT?
YES
IMPROPER GROUND.
LED: OFF
CONTROL WILL NOT RESPOND TO CALL FOR HEAT
UNTIL PROPER GROUND.
NO
IS THERE A PROPER GROUND?
YES
NO
LED: ON STEADY
IGNITOR WILL GLOW DIMLY BUT WILL NOT LIGHT
IS VOLTAGE
ABOVE 90 VOLTS?
YES
ROLLOUT SWITCH CLOSED?
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
INDOOR BLOWER ON.
LED: 5 FLASHES
SEQUENCE HOLDS UNTIL ROLLOUT SWITCH CLOSES
AND POWER IS RESET OR T'STAT IS INTERRUPTED
FOR MINIMUM OF 1 SECOND.
NO
YES
BURNER OFF?
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
INDOOR BLOWER ON HEATING SPEED.
LED: 1 FLASH
NO
(Contiuous Flame Check)
YES
NO
NORMAL OPERATION:
LED: STEADY ON
YES
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER ON
LED: 4 FLASHES
THERMOSTAT CALLS FOR HEAT:
LED: STEADY ON
NO
YES
PRIMARY AND SECONDARY LIMIT SWITCH.
CLOSED?
YES
NO
IS COMBUSTION AIR
PRESSURE SWITCH OPEN?
YES
GAS VALVE OFF.
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF WITH DELAY.
LED: 2 FLASHES
(Sequence holds until pressure switch
opens or thermostat resets control.)
IS COMBUSTION AIR INDUCER
ENERGIZED?
YES
HAS COMBUSTION AIR PRESSURE
SWITCH CLOSED IN 2.5 MINUTES?
NO
YES
CONTINUED NEXT PAGE
Page 23
PRESSURE SWITCH IS IN WATCHGUARD MODE.
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF WITH DELAY.
LED: 3 FLASHES
IS 5‐MINUTE RESET PERIOD COMPLETE?
YES
Troubleshooting: Heating Sequence of Operation (Continued)
HEATING SEQUENCE CONTINUED
NORMAL HEATING MODE
ABNORMAL HEATING MODE
15‐SECOND COMBUSTION AIR INDUCER PREPURGE
INITIATED BY CLOSED PRESSURE SWITCH.
YES
NO
IS VOLTAGE ABOVE 90 VOLTS?
IGNITOR WARM‐UP -- 20 SECONDS.
YES
NO
YES
4‐SECOND TRIAL FOR IGNITION.
GAS VALVE OPENS.
LED: ON STEADY
UNTIL VOLTAGE IS
ABOVE 95 VOLTS,
THEN RESTARTS
HEATING
SEQUENCE.
GAS VALVE OFF. COMBUSTION AIR INDUCER ON.
INDOOR BLOWER OFF.
NO
HAS CONTROL FAILED TO SENSE FLAME FOR
FIVE CONSECUTIVE TRIES DURING A SINGLE
HEAT DEMAND?
YES
FLAME STABILIZATION PERIOD.
4 SECONDS
FLAME RECTIFICATION CURRENT
CHECK. CAN FLAME BE PROVEN WITHIN
4 SECONDS AFTER GAS VALVE OPENS?
NO
YES
WATCHGUARD MODE. GAS VALVE OFF.
COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF WITH DELAY
LED: 7 FLASHES WATCHGUARD FAILURE CODE.
IS 60‐MINUTE RESET PERIOD COMPLETE?
YES
YES
NO
NO
HAS CONTROL RESET IGNITION
SEQUENCE FOUR TIMES?
FLAME PRESENT?
YES
NO
FLAME SIGNAL 1.5 MICROAMPS OR GREATER?
YES
INDOOR BLOWER ON
AFTER 30-SECOND DELAY
YES
PRIMARY AND SECONDARY LIMIT
SWITCHES CLOSED?
NO
LOW FLAME SIGNAL
(Does not affect operation of control)
LED: ON STEADY
GAS VALVE DE-ENERGIZED.
COMBUSTION AIR INDUCER DE-ENERGIZED.
INDOOR BLOWER ON UNTIL SWITCH CLOSES.
LED: 4 FLASHES
IS LIMIT SWITCH CLOSED?
YES
NO
YES
NO
NO
ROLLOUT SWITCH CLOSED?
YES
COMBUSTION AIR PRESSURE
SWITCH CLOSED?
YES
THERMOSTAT DEMAND SATISFIED.
YES
LED: ON STEADY
YES
COMB. AIR INDUCER CONTINUES 15‐SECOND
POST PURGE AFTER T'STAT DEMAND IS SATISFIED.
INDOOR AIR BLOWER COMPLETES SELECTED “OFF”
DELAY BEFORE SHUTTING OFF.
NO
5 MINUTE WATCHGUARD MODE.
HAS LIMIT SWITCHED CLOSED
AFTER 5 MINUTES?
YES
GAS VALVE POWER OFF.
COMBUSTION AIR INDUCER POWER ON AFTER 15
SECOND DELAY. INDOOR BLOWER ON
LED: 5 FLASHES
SEQUENCE HOLDS UNTIL ROLLOUT SWITCH IS RESET
AND MAIN POWER IS INTERRUPTED OR
THERMOSTAT IS CYCLED OFF/ON FOR 1 SEC. MINIMUM.
HAS PRESSURE SWITCH OPENED 5
TIMES IN THE SAME HEAT DEMAND?
NO
GAS VALVE DE-ENERGIZED.
COMBUSTION AIR INDUCER ON.
INDOOR BLOWER OFF WITH DELAY
LED: 6 FLASHES 5 MINUTE PRESSURE
SWITCH WATCHGUARD MODE.
Page 24
1 HR
PRESSURE
SWITCH
YES
WATCHGUARD
MODE
Troubleshooting: Cooling Sequence of Operation
COOLING SEQUENCE OF OPERATION
NORMAL COOLING MODE
ABNORMAL COOLING MODE
POWER ON
IGNITION CONTROL MAIN POWER ON. LED: ON STEADY
NO
CONTROL SELF DIAGNOSTIC CHECK.
IS CONTROL OPERATING NORMALLY?
GAS VALVE OFF. COMBUSTION AIR INDUCER OFF.
INDOOR BLOWER OFF WITH NORMAL DELAY.
LED: OFF
INTERRUPT MAIN POWER TO RESET CONTROL.
YES
NO
IS THERE A PROPER GROUND?
LED: ON STEADY
CONTROL WILL CONTINUE TO CALL FOR COOLING
IN THIS CONDITION.
YES
NO
IS POLARITY CORRECT?
LED: 9 FLASHES
CONTROL WILL CONTINUE TO CALL FOR COOLING
IN THIS CONDITION.
YES
NO
LED: ON STEADY.
CONTROL WILL CONTINUE TO CALL FOR
COOLING IN THIS CONDITION.
IS VOLTAGE
ABOVE 90 VOLTS?
YES
LED: ON STEADY.
REMAINS UNCHANGED THROUGHOUT COOLING CYCLE.
THERMOSTAT CALLS FOR COOLING.
COMPRESSOR CONTACTOR AND SYSTEM FAN
ENERGIZED WITH 2‐SECOND DELAY
(COOLING SPEED). EAC TERM. ENERGIZED.
THERMOSTAT OPENS.
COMPRESSOR OFF.
SYSTEM FAN AND EAC TERM. OFF
WITH 60‐SECOND DELAY.
Page 25
Troubleshooting: Continuous Fan Sequence of Operation
CONTINUOUS FAN SEQUENCE OF OPERATION
LED: ON STEADY
MANUAL FAN SELECTION MADE AT THERMOSTAT.
CONTROL (G) ENERGIZES SYSTEM FAN ON CONTINUOUS
BLOWER SPEED. EAC TERMINAL IS ENERGIZED.
THERMOSTAT CALLS FOR HEAT (W).
YES
NO
SYSTEM FAN SWITCHES TO
HEATING SPEED.
THERMOSTAT CALLS FOR COOLING.
YES
SYSTEM FAN SWITCHED TO COOL SPEED.
EAC TERM. REMAINS ON.
HUM TERM. ENERGIZES
WITH COMB. AIR INDUCER.
NO
THERMOSTAT OPENS.
HUM TERM. DE-ENERGIZES
WITH COMB. AIR INDUCER
THERMOSTAT OPENS.
MANUAL FAN SELECTION MADE AT THERMOSTAT.
CONTROL (G) ENERGIZES SYSTEM FAN ON
CONTINUOUS BLOWER SPEED.
Page 26
SYSTEM FAN SWITCHES TO
CONTINUOUS BLOWER SPEED
.
VIII- TWINNING
Twinning 2 ML180DF Furnaces
The control board in this furnace is equipped with a provi­
sion to ”twin” (interconnect) two(2) adjacent furnaces with a
common plenum such that they operate as one (1) large
unit.
between the ”C” and ”Twin” terminals of the two controls.
The 24 VAC secondary of the two systems must be in
phase. All thermostat connections are made to one control
only. Figure 20 show wiring for two-stage and single stage
thermostats.
When twinned, the circulating blower speeds are synchro­
nized between the furnaces. If either furnace has a need to
run the blower, both furnaces will run the blower on the
same speed. The cooling speed has highest priority, fol­
lowed by heating speed and fan speed.
The twinned furnace without thermostat connections is to
have the call for heat supplied by an external 24VAC isola­
tion relay to prevent its rollout switch from being bypassed
by the other twinned furnace. The coil of the isolation relay
connects from the thermostat ”W” to 24 VAC common. The
contacts of the relay connect ”R” to ”W” on the non-thermo­
stat twin.
Field installation of twinning consists of connecting wires
FIELD WIRING FOR TWINNING THE ML180DF
TWO-STAGE THERMOSTAT
TWIN
R
SINGLE STAGE THERMOSTAT
R
R
TWIN 1
Y
TWIN 1
Y
Y
Y
Call For Fan
Call For Fan
G
Call For 2nd
StageHeat
R
Call For Cool
Call For Cool
Call For 1st
Stage Heat
TWIN
G
G
G
Call For Heat
W
W1
W2
W
W
C
C
TWIN
TWIN
ISOLATION
RELAY
ISOLATION
RELAY
R
R
TWIN 2
TWIN 2
Y
Y
G
G
W
W
C
C
FIGURE 20
Page 27