Lennox ML193DF045P36B Installation and operation manual

Page 1 ©2014 Lennox Industries Inc.
Litho U.S.A.
Corp. 1026-L5 ML193DF
Service Literature Revised 03-2014
ML193DF SERIES UNITS
ML193DF series units are high-efficiency gas furnaces
manufactured with Lennox DuralokPlustaluminized steel
clamshell-type heat exchangers, with a stainless steel con
densing coil. ML193DF units are available in heating input
capacities of 44,000 to 110,000 Btuh (13 to 32.2 kW) and
cooling applications from 2 through 5 tons (7.0 through
17.6 kW). Refer to Engineering Handbook for proper siz
ing.
Units are factory equipped for use with natural gas. A kit is
available for conversion to LPG operation. All ML193DF
units are equipped with a hot surface ignition system. The
gas valve is redundant to assure safety shut-off as required
by C.S.A.
The heat exchanger, burners and manifold assembly can
be removed for inspection and service. The maintenance
section gives a detailed description on how this is done.
All specifications are subject to change. Procedures out
lined in this manual are presented as a recommendation
only and do not supersede or replace local or state codes.
WARNING
Electric shock hazard. Can cause injury
or death. Before attempting to perform
any service or maintenance, turn the
electrical power to unit OFF at discon
nect switch(es). Unit may have multiple
power supplies.
Table of Contents
Specifications 2.................................
Optional Accessories 3..........................
Blower Performance Data 4......................
I-Unit Components 6............................
II Placement and Installation 18....................
III-Start-Up 36...................................
IV-Heating System Service Checks 37..............
V-Typical Operating Conditions 39.................
VI-Maintenance 40...............................
VII-Wiring and Sequence of Operation 42...........
WARNING
Improper installation, adjustment, alteration, service
or maintenance can cause property damage, person
al injury or loss of life. Installation and service must
be performed by a licensed professional HVAC in
staller (or equivalent), service agency or the gas sup
plier.
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. ML193DF045P36B ML193DF070P36B ML193DF090P48C ML193DF110P60C
1AFUE 93% 93% 93% 93%
Input - Btuh 44,000 66,000 88,000 110,000
Output - Btuh 41,000 61,000 82,000 102,000
Temperature rise range - °F 25 - 55 50 - 80 40 - 70 50 - 80
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
3.5 / 10.0 3.5 / 10.0 3.5 / 10.0 3.5 / 10.0
High static - in. w.g. 0.50 0.50 0.50 0.50
Connections
in.
Intake / Exhaust Pipe (PVC) 2 / 2 2 / 2 2 / 2 2 / 2
Gas pipe size IPS 1/2 1/2 1/2 1/2
Condensate Drain Trap (PVC pipe) - i.d. 1/2 1/2 1/2 1/2
with eld supplied (PVC coupling) - o.d. 3/4 3/4 3/4 3/4
Indoor
Blower
Wheel nom. dia. x width - in. 10 x 8 10 x 8 10 x 10 11 ½ x 10
Motor output - hp 1/3 1/3 1/2 1
Tons of add-on cooling 2.5 - 3 2.5 - 3 3 - 4 4 - 5
Air Volume Range - cfm 605 - 1615 560 - 1550 920 - 2145 1210 - 2410
Electrical
Data
Voltage 120 volts - 60 hertz - 1 phase
Blower motor full load amps 6.1 6.1 8.2 11.5
Maximum overcurrent protection 15 15 15 15
Shipping Data lbs. - 1 package 124 129 147 162
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
OPTIONAL ACCESSORIES - MUST BE ORDERED EXTRA
“B” Width Models “C” Width Models
CABINET ACCESSORIES
Downow Combustible Flooring Base 11M60 11M61
CONDENSATE DRAIN KITS
Condensate Drain Heat Cable 6 ft. 26K68 26K68
24 ft. 26K69 26K69
50 ft. 26K70 26K70
Heat Cable Tape Fiberglass - 1/2 in. x 66 ft. 36G53 36G53
Aluminum foil - 2 in. x 60 ft. 16P89 16P89
Crawl Space Vent Drain Kit 51W18 51W18
CONTROLS
Twinning Kit 65W80 65W80
DOWNFLOW FILTER KITS
Downow Air Filter and Rack Kit 51W07 51W08
No. and Size of lter - in. (2) 20 x 20 x 1 (2) 20 x 20 x 1
NIGHT SERVICE KITS
Night Service Kit 51W03 51W03
TERMINATION KITS
See Installation Instructions for specic venting information.
Termination Kits -
Direct Vent Applications
Only
Concentric US - 2 in. 71M80 69M29
3 in. - - - 60L46
Canada - 2 in. 44W92 44W92
3 in. - - - 44W93
Flush-Mount 2, 2-1/2 or 3 in. 51W11 51W11
Wall - Close
Couple
US - 2 in. 22G44 - - -
3 in. 44J40 44J40
Wall - Close
Couple WTK
Canada - 2 in. 30G28 - - -
3 in. 81J20 81J20
Termination Kits -
Direct or Non-Direct vent
Roof 2 in. 15F75 15F75
Wall Ring Kit 2 in. 15F74 315F74
Roof Termination Flashing Kit - Direct or Non-Direct Vent -
Contains two ashings
44J41 44J41
1 Cleanable polyurethane frame type lter.
2 Kits contain enough parts for two, non−direct vent installations.
3 Non-direct vent only.
NOTE - Termination Kits 44W92, 44W93, 30G28, 81J20 are certied to ULC S636 standard for use in Canada only.
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
4501 - 7500 ft. 7501 - 10,000 ft. 0 - 7500 ft. 0 - 7500 ft. 7501- 10,000 ft.
all models 74W90 74W91 69W73 73W81 73W37

Page 4
BLOWER DATA
ML193DF070XP36B 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
0.00 1505 660 1310 570 1090 455 940 390
0.10 1480 625 1295 550 1070 435 935 365
0.20 1405 585 1255 515 1055 425 930 350
0.30 1355 580 1225 475 1045 405 900 330
0.40 1305 540 1165 470 1010 385 890 325
0.50 1270 525 1110 425 975 370 835 305
0.60 1175 500 1080 415 925 345 815 290
0.70 1105 460 1000 395 855 320 745 270
0.80 1040 440 925 365 790 300 670 250
0.90 920 400 825 335 680 270 560 225
ML193DF110XP60C 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
0.00 2410 1390 2190 1080 1860 910 1560 735
0.10 2405 1385 2180 1070 1855 905 1555 730
0.20 2285 1345 2120 1030 1850 865 1540 720
0.30 2220 1315 2015 1005 1770 840 1535 705
0.40 2185 1295 1950 955 1750 815 1530 685
0.50 2045 1240 1830 925 1680 790 1500 660
0.60 1965 1220 1710 890 1575 755 1445 640
0.70 1820 1165 1610 850 1495 720 1370 615
0.80 1625 1155 1510 820 1400 695 1315 595
0.90 1455 1110 1390 790 1350 660 1210 565
ML193DF045XP36B 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
0.00 1615 650 1385 555 1205 465 1045 390
0.10 1605 640 1375 545 1195 455 1035 380
0.20 1500 620 1340 525 1165 445 1015 370
0.30 1450 590 1290 490 1125 420 975 365
0.40 1350 560 1235 480 1090 405 920 345
0.50 1300 545 1170 450 1035 380 875 335
0.60 1195 500 1095 425 990 365 840 320
0.70 1140 485 1020 400 895 345 780 300
0.80 1025 450 920 370 840 330 695 275
0.90 945 435 800 335 700 295 605 250
ML193DF090XP48C 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
0.00 2075 800 1890 720 1625 645 1375 535
0.10 1995 755 1830 680 1590 615 1350 515
0.20 1910 715 1775 645 1575 580 1340 500
0.30 1825 680 1705 610 1530 550 1325 485
0.40 1730 645 1620 580 1475 525 1285 460
0.50 1630 615 1530 545 1405 500 1240 440
0.60 1530 585 1450 525 1330 470 1175 420
0.70 1430 555 1340 485 1260 450 1095 390
0.80 1300 525 1245 465 1145 415 1015 370
0.90 1185 495 1110 430 1045 385 915 340

Page 5
FIGURE 1
CONTROL BOX
(Includes integrated control,
transformer and door switch)
BAG ASSEMBLY
BLOWER MOTOR
(hidden)
BLOWER
ACCESS
PANEL
BURNER
ACCESS
PANEL
COMBUSTION
AIR INDUCER
BURNER BOX ASSEMBLY
(includes sensor, rollout switches and ignitor)
GAS VALVE
BLOWER DECK
HEAT EXCHANGER
COLD END HEADER BOX
PRIMARY LIMIT
PARTS ARRANGEMENT

Page 6
I-UNIT COMPONENTS
ML193DF unit components are shown in figure 1. The
combustion air inducer, gas valve and burners can be ac
cessed by removing the burner access panel. The blower
and control box can be accessed by removing the blower
access door.
A-Control Box Components (Figure 2)
Unit transformer (T1) and integrated ignition control (A92)
are located in the control box. In addition, a door interlock
switch (S51) is located in the control box.
FIGURE 2
DOOR INTERLOCK
SWITCH (S51)
INTEGRATED IGNITION
CONTROL
(A92)
TRANSFORMER
(T1)
ML193DF Control Box
1. Transformer (T1)
A transformer located in the control box provides power to
the low voltage section of the unit. The transformers on all
models are rated at 40VA with a 120V primary and 24V
secondary.
2. Door Interlock Switch (S51)
A door interlock switch rated 14A at 120VAC is located on
the control box. The switch is wired in series with line volt
age. When the blower door is removed the unit will shut
down.
3. Integrated Ignition Control 100973 (A92)
CAUTION
Electrostatic discharge can affect elec
tronic components. Take precautions
to neutralize electrostatic charge by
touching your hand and tools to metal
prior to handling the control.
WARNING
Shock hazard.
Disconnect power before servicing. Control is not
field repairable. If control is inoperable, simply re
place entire control.
Can cause injury or death. Unsafe operation will
result if repair is attempted.
The ignition control system consists of an integrated con
trol (figure 4) ignitor (figure 10) and sensor (figure 10). The
integrated control and ignitor work in combination to en
sure furnace ignition and ignitor durability. The integrated
control, controls all maor furnace operations. The inte
grated control also features two LED lights (DS1 red and
DS2 green) for troubleshooting and two accessory termi
nals rated at (1) one amp. The integrated control also fea
tures a (3) amp fuse for overcurrent protection. Tables 1
and 2 show jack plug terminal designations. See table 3 for
troubleshooting diagnostic codes. The 95 volt ignitor is
made from a high strength, silicon nitride material that pro
vides long life and trouble free maintenance. The inte
grated control continuously monitors line voltage and
maintains the ignitor power at a consistent level to provide
proper lighting and maximum ignitor life.
TABLE 1
4-Pin Terminal Designation
PIN # FUNCTION
1Combustion Air Inducer Line
2Ignitor Line
3Combustion Air Inducer Neutral
4Ignitor Neutral
TABLE 2
12-Pin Terminal Designations
PIN # FUNCTION
1High Limit Output
2Not Used
324V Line
4Not Used
5Rollout Switch Out
624V Neutral
7High Limit Input
8 Ground
9Gas Valve Common
10 Pressure Switch In
11 Rollout Switch In
12 Gas Valve Out
Electronic Ignition (See Figure 5)
On a call for heat the integrated control monitors the com
bustion air inducer prove switch. The integrated control will
not begin the heating cycle if the prove switch is closed (by-
passed). Once the prove switch is determined to be open,
the combustion air inducer is energized. When the differen

Page 7
tial in the prove switch is great enough, the prove switch
closes and a 15-second pre-purge begins. If the prove
switch is not proven within 2-1/2 minutes, the 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 during the 4 second trial. If ignition is not
proved during the 4-second period, the integrated control
will try four more times with an inter purge and warm-up
time between trials of 35 seconds. After a total of five trials
for ignition (including the initial trial), the integrated control
goes into Watchguard-Flame Failure mode. After a
60-minute reset period, the integrated control will begin the
ignition sequence again.
The integrated control has an added feature of ignitor pow
er regulation to maintain consistent lighting and longer igni
tor life under all line voltage conditions.
Fan Control
The fan on time of 30 seconds is not adjustable. The fan off
delay (amount of time that the blower operates after the
heat demand has been satisfied) may be adjusted by
changing the jumper position across the five pins on the
integrated control. The unit is shipped with a factory fan off
setting of 90 seconds. The fan off delay affects comfort and
is adjustable to satisfy individual applications. Adjust the
fan off delay to achieve a supply air temperature between
90° and 110°F at the moment that the blower is de-ener
gized. Longer off delay settings provide lower return air
temperatures; shorter settings provide higher return air
temperatures. See figure 3.
FIGURE 3
FAN‐OFF TIME IN SECONDS
To adjust fan-off timing, reposition jumper across pins
to achieve desired setting.
NO JUMPER
FIGURE 4
INTEGRATED CONTROL
(Automatic Hot Surface Ignition System)
TERMINAL DESIGNATIONS
HUM
LINE
XFMR
EAC
COOL
HEAT
PARK
FLAME
NEUTRALS
Humidifier (120VAC)
Input (120VAC)
Transformer (120VAC)
Electronic Air Cleaner (120VAC)
Blower - Cooling Speed (120VAC)
Blower - Heating Speed (120VAC)
Dead terminals to park alternate spd taps
Flame sensor
Neutral terminals (120VAC)
3 AMP, 32 VAC FUSE
BLOWER OFF
DELAY JUMPER
LED 1 LED 2

Page 8
The integrated control is equipped with two LED lights for troubleshooting. The diagnostic codes are listed below in table 3.
TABLE 3
DIAGNOSTIC CODES
Make sure to Identify LED'S Correctly.
LED #1 (Red) LED #2 (Green) DESCRIPTION
SIMULTANEOUS
SLOW FLASH
SIMULTANEOUS
SLOW FLASH
Power on - Normal operation.
Also signaled during cooling and continuous fan.
SIMULTANEOUS
FAST FLASH
SIMULTANEOUS
FAST FLASH Normal operation - signaled when heating demand initiated at thermostat.
SLOW FLASH ON Primary or secondary limit switch open. Limit must close within 3 minutes or unit
goes into 1 hour Watchguard.
OFF SLOW FLASH
Pressure prove switch open.
OR: Blocked inlet/exhaust vent;
OR: Pressure switch closed prior to activation of combustion air inducer.
ALTERNATING
SLOW FLASH
ALTERNATING
SLOW FLASH
Watchguard 1 hour -- burners failed to ignite or lost flame 5 times during single
heating demand.
SLOW FLASH OFF Flame sensed without gas valve energized.
ON SLOW FLASH Rollout switch open. OR: 12‐pin connector improperly attached.
ON
ON
OFF
ON
OFF
ON
Circuit control failure or control wired incorrectly.
FAST FLASH SLOW FLASH Main power polarity reversed. Switch line and neutral.
SLOW FLASH FAST FLASH Low flame signal. Measures below 1.5 microamps. Replace flame sense rod.
ALTERNATING
FAST FLASH
ALTERNATING
FAST FLASH
Improper main ground.
OR: Line voltage below 90 volts.
NOTE - Slow flash rate equals 1 Hz (one flash per second). Fast flash rate equals 3 Hz (three flashes per second).
Minimum flame sense current = 0.5 microAmps.
FIGURE 5
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉ
É
É
DEMAND
CAI
GAS VALVE
ON
OFF
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
É
É
ÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉ
IGNITOR
15 Sec.
Pre -Purge
20 sec.
Ignitor Warmup
*4 Sec.Trial
for Ign.
Post
Purge
5 SEC
**Blower on time will be 45 seconds after gas valve is energized. Blower off time will depend on “OFF TIME” Setting.
INDOOR BLOWER
ÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉ
**Blower “On”
Delay
End of
Heat Demand Blower
Off
Time
*Ignitor will energize the first 3 seconds of the 4 second trial for ignition

Page 9
4. Integrated Ignition Control 103085 (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 6 with control terminal designations
in tables 4 and 5), flame sensor and ignitor (figure 10). The
integrated control and ignitor work in combination to en
sure furnace ignition and ignitor durability. The integrated
control, controls all major furnace operations. The inte
grated control also features a RED LED for troubleshooting
and two accessory terminals rated at (1) one amp. See
table 6 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 7)
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 the 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.
TABLE 4
4-Pin Terminal Designation
PIN # FUNCTION
1Combustion Air Inducer Line
2Ignitor Line
3Combustion Air Inducer Neutral
4Ignitor Neutral
TABLE 5
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
TABLE 6
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.
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.

Page 10
FIGURE 6
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
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉÉ
ÉÉ
39
ÉÉÉÉÉÉÉÉÉÉ
IGNITOR
351
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
ÉÉÉÉÉÉÉÉÉ
Blower “On”*
Delay
ELECTRONIC IGNITION
FIGURE 7

Page 11
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 8.
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 8
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
Twinning 2 ML193DF Furnaces
Integrated control 103085 is equipped with a provision to
”twin” (interconnect) two(2) adjacent furnaces with a com
mon plenum such that they operate as one (1) large unit.
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.
Field installation of twinning consists of connecting wires
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 9 show wiring for two-stage and single stage
thermostats.
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.

Page 12
FIGURE 9
Y
W
C
Y
W
R
R
G
C
G
TWIN
TWIN
TWIN 2
TWIN 1
ISOLATION
RELAY
TWO-STAGE THERMOSTAT
Call For Cool
Call For Fan
Call For 1st
Stage Heat
Call For 2nd
StageHeat
R
Y
G
W1
W2
Y
W
C
Y
W
R
R
G
C
G
TWIN
TWIN
TWIN 2
TWIN 1
ISOLATION
RELAY
Call For Cool
Call For Fan
Call For Heat
R
Y
G
W
SINGLE STAGE THERMOSTAT
FIELD WIRING FOR TWINNING THE ML193DF

Page 13
B-Heating Components
Combustion air inducer (B6), primary limit control (S10),
SureLight ignitor, burners, flame rollout switch (S47), gas
valve (GV1), combustion air prove switch (S18), and clam
shell heat exchangers are located in the heating compart
ment. The heating compartment can be accessed by re
moving the burner access panel.
1. Ignitor (Figure 10)
ML193DF units use a mini-nitride ignitor made from a pro
prietary ceramic material. Ignitor longevity is enhanced by
controlling the voltage to the ignitor. Units equipped with
control 103085 have a 120V ignitor. Units equipped with
control 100973 have a 95V ignitor. See figure 11 and table
7 for resistance and voltage checks.
2. Flame Sensor (Figure 10)
A flame sensor is located on the left side of the burner sup
port. The sensor is mounted on the bottom burner box plate
and the tip protrudes into the flame envelope of the left-
most burner. The sensor can be removed for service with
out removing any part of the burners. During operation,
flame is sensed by current passed through the flame and
sensing electrode. The ignition control allows the gas valve
to remain open as long as flame signal is sensed.
NOTE - The ML193DF furnace contains electronic
components that are polarity sensitive. Make sure that
the furnace is wired correctly and is properly grounded.
3. Flame Rollout Switches (Figure 10)
Flame rollout switches S47 are SPST N.C. high tempera
ture limits located on the top left and bottom right of the front
buner box plate. S47 is wired to the burner ignition control
A92. When either of the switches sense flame rollout (indi
cating a blockage in the combustion passages), the flame
rollout switch trips, and the ignition control immediately
closes the gas valve. Switch S47 in all ML193DF units is
factory preset to open at 250_F + 12_F (121_C + 6.7_C) on
a temperature rise. All flame rollout switches are manual
reset.
FIGURE 10
ML193DF Burner Box Assembly
SENSOR
ROLLOUT SWITCHES
GAS VALVE
IGNITOR
BURNERS
FRONT BURNER BOX PLATE

Page 14
FIGURE 11
Test 1
Check ignitor circuit for correct resistance.
Remove 4-pin plug from control.
Check ohms reading across terminals 2 and 4.
See table 7. If value is correct, this is the only test
needed. If the reading on the meter is not correct, (0 or
infinity) then a second test is needed.
Test 2
Check ignitor for correct resistance.
Seperate the 2-pin jack-plug near the manifold and check
resistance of ignitor at the plug. See table 7. 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. See
table 7. If voltage reads below these values, check for
correct supply voltage to furnace.
Test 1
Test 2
Test 3 Integrated Control Detail
Integrated Control DetailIntegrated Control Detail
Integrated Control Detail
IGNITOR CHECKS
Multi−Meter
(set to ohms)
Multi−Meter
(set to ohms)
Multi−Meter
(set to VAC)
Control Ohms
103085
100973 24 to 47
39 to 70
Voltage + 10%
120
95
TABLE 7

Page 15
4. Primary Limit Control (Figure 12)
Primary limit (S10) used on ML193DF units is located in the
heating vestibule panel. When excess heat is sensed in the
heat exchanger, the limit will open. Once the limit opens,
the furnace control energizes the supply air blower and de-
energizes the gas valve. The limit automatically resets
when unit temperature returns to normal. The switch is fac
tory set and cannot be adjusted. For limit replacement re
move wires from limit terminals and rotate limit switch 90
degrees. Slowly remove from the vestibule panel. Install
replacement limit with same care.
FIGURE 12
Primary Limit Location and Heat Exchanger
Install limit face down
5. Heat Exchanger (Figure 12)
ML193DF units use an aluminized steel primary and stain
less steel secondary heat exchanger assembly. Heat is
transferred to the air stream from all surfaces of the heat
exchanger. The shape of the heat exchanger ensures
maximum efficiency.
The combustion air inducer pulls fresh air through the burn
er box. This air is mixed with gas in the burners. The gas /
air mixture is then burned at the entrance of each clam
shell. Combustion gases are then pulled through the pri
mary and secondary heat exchangers and exhausted out
the exhaust vent pipe.
6. Burners (Figure 13)
All units use inshot burners. Burners are factory set and do
not require adjustment. Burners can be removed as an as
sembly for service. Burner maintenance and service is de
tailed in the MAINTENANCE section of this manual. Each
burner uses an orifice which is precisely matched to the
burner input. See table 8 for orifice size. The burner is sup
ported by the orifice and will easily slide off for service. A
flame retention ring in the end of each burner maintains
correct flame length and shape and keeps the flame from
lifting off the burner head.
TABLE 8
Gas Orifice Size
Unit Fuel Orifice Size
All Natural 0.0625
All L.P./Propane 0.034
FIGURE 13
Burner Detail Top Vie
w
SENSOR
IGNITOR
ORIFICES
7. Gas Valve (GV1)
The ML193DF uses an internally redundant to valve to as
sure safety shut‐off. If the gas valve must be replaced, the
same type valve must be used.
24VAC terminals and gas control switch are located on top
of the valve. All terminals on the gas valve are connected to
wires from the ignition control. 24V applied to the terminals
opens the valve.
Inlet and outlet pressure taps are located on the valve. A
manifold adjustment screw is also located on the valve. An
LPG changeover kit is available.
FIGURE 14
Gas Valve
MANIFOLD
PRESSURE
OUTLET
PORT
INLET
PRESSURE
PORT
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
(under
barbed
fitting)

Page 16
8. Combustion Air Inducer (B6)
& Cold End Header Box
All ML193DF units use a combustion air inducer to move air
through the burners and heat exchanger during heating op
eration. The blower uses a shaded pole 120VAC motor.
The motor operates during all heating operation and is con
trolled by burner ignition control A3. Blower operates con
tinuously while there is a call for heat. The burner ignition
control will not proceed with the ignition sequence until
combustion air inducer operation is sensed by the proving
switches.
The CAI is installed on the cold end header box. The cold
end header box is a single piece made of hard plastic. The
box has an internal channel where the combustion air in
ducer creates negative pressure at unit start up. The chan
nel contains an orifice used to regulate flow created by the
CAI. The box has pressure taps for the CAI pressure switch
hoses. The pressure switch measure the pressure across
the CAI orifice or difference in the channel and the box. If
replacement is necessary the gaskets used to seal the
box to the vestibule panel and the CAI to the box, must
also be replaced.
TABLE 9
ML193DF Unit C.A.I. Orifice Size
-045 0.618
-070 0.891
-090 1.031
-110 1.297
9. Combustion Air Pressure Switch
(Figure 15)
ML193DF series units are equipped with a differential pres
sure switch located on the cold end header box. The
switches monitor across the CAI orifice to insure proper
flow through the heat exchanger.
The switch is a SPST N.O. prove switch electrically con
nected to the integrated control. The purpose of the switch
is to prevent burner operation if the combustion air inducer
is not moving enough air for proper combustion.
FIGURE 15
Pressure Switch
24VAC
TERMINALS
BRACKET
TAP
TAP
On start‐up, the switch senses that the combustion air in
ducer is operating. It closes a circuit to the ignition control
when the difference in pressure across the CAI orifice ex
ceeds a non-adjustable factory setting. If the switch does
not successfully sense the required differential, the switch
cannot close and the furnace cannot operate. If the flue or
air inlet become obstructed during operation, the switch
senses a loss of pressure differential and opens the circuit
to the ignition control. If the condensate line is blocked, wa
ter will back up into the header box and reduce the pressure
differential across the switch. The prove switch opens if the
differential drops below the set point. See table 10.
Checks of pressure differential can aid in troubleshooting.
When measuring the pressure differential, readings should
be taken at the pressure switch. See figure 16. Lack of dif
ferential usually indicates problems in the intake or exhaust
piping, but may indicate problems in the heat exchanger,
condensing coil, header boxes, combustion inducer or oth
er components.
TABLE 10
ML193DF
Altitude ft
0 - 4500 4501 -
7500 7501 - 10000
Set Point SetPoint Set Point
-045
-0.65 -0.60 -0.55
-070
-090
-110
*Set point is factory set and non-adjustable

Page 17
FIGURE 16
1 - Remove thermostat demand and allow unit to cycle off.
2 - Install a tee in the negative (-) line (red tubing) and a tee in the
positive (+) line (black tubing) running from the pressure
switch to the cold end header box.
3 - Install a manometer with hose from the negative (-) side of
the manometer to the tee installed in the negative (-) line and
with hose from the positive (+) side of the manometer to the
tee in the positive (+) line.
NOTE - Both sides of the cold end header box are negative. How
ever the (+) port reads less negative pressure than the (-) port.
4 - Operate unit and observe manometer reading.
Readings will change as heat exchanger warms.
a. Take one reading immediately after start‐up.
b. Take a second reading after unit has reached steady
state (approximately 5 minutes). This will be the pressure
differential.
The pressure differential should be greater
than those listed in table 10.
5 - Remove thermostat demand and allow to cycle off.
6 - Remove manometer and tee's. Reinstall combustion air
sensing hoses to the pressure switch.
BLACK TUBING
POSITIVE
RED TUBING
NEGATIVE
Measuring Pressure Differential
C-Blower Compartment
Blower motor (B3) and capacitor (C4), are located in the
blower compartment. The blower compartment can be ac
cessed by removing the blower access panel.
FIGURE 17
Blower Motor Housing
To Remove Blower From Unit: Disconnect Power, Remove Control
Box, Remove Bolts and Unplug Motor Wires From Control Board.
Then Slide Out Front of Unit.
MOTOR
CAPACITOR
BOLTS
1.Blower Motor (B3) and Capacitor (C4)
All ML193DF units use single-phase direct-drive blower
motors. All motors are 120V permanent split capacitor mo
tors to ensure maximum efficiency. See SPECIFI
CATIONS table at the front of this manual for more detail.
See motor nameplate for capacitor ratings.

Page 18
II-PLACEMENT AND INSTALLATION
Pipe & Fittings Specifications
All pipe, fittings, primer and solvent cement must conform
with American National Standard Institute and the Ameri
can Society for Testing and Materials (ANSI/ASTM) stan
dards. The solvent shall be free flowing and contain no
lumps, undissolved particles or any foreign matter that ad
versely affects the joint strength or chemical resistance of
the cement. The cement shall show no gelation, stratifica
tion, or separation that cannot be removed by stirring. Re
fer to the table 11 below for approved piping and fitting ma
terials.
CAUTION
Solvent cements for plastic pipe are flammable liq
uids and should be kept away from all sources of
ignition. Do not use excessive amounts of solvent
cement when making joints. Good ventilation should
be maintained to reduce fire hazard and to minimize
breathing of solvent vapors. Avoid contact of ce
ment with skin and eyes.
TABLE 11
PIPING AND FITTINGS SPECIFICATIONS
Schedule 40 PVC (Pipe) D1785
Schedule 40 PVC (Cellular Core Pipe) F891
Schedule 40 PVC (Fittings) D2466
Schedule 40 CPVC (Pipe) F441
Schedule 40 CPVC (Fittings) F438
SDR-21 PVC or SDR-26 PVC (Pipe) D2241
SDR-21 CPVC or SDR-26 CPVC (Pipe) F442
Schedule 40 ABS Cellular Core DWV (Pipe) F628
Schedule 40 ABS (Pipe) D1527
Schedule 40 ABS (Fittings) D2468
ABS-DWV (Drain Waste & Vent)
(Pipe & Fittings) D2661
PVC-DWV (Drain Waste & Vent)
Pipe & Fittings) D2665
PRIMER & SOLVENT CEMENT ASTM
SPECIFICATION
PVC & CPVC Primer F656
PVC Solvent Cement D2564
CPVC Solvent Cement F493
ABS Solvent Cement D2235
PVC/CPVC/ABS All Purpose Cement For
Fittings & Pipe of the same material D2564, D2235, F493
ABS to PVC or CPVC Transition Solvent
Cement D3138
CANADA PIPE & FITTING & SOLVENT
CEMENT MARKING
PVC & CPVC Pipe and Fittings
ULCS636
PVC & CPVC Solvent Cement
ABS to PVC or CPVC Transition Cement
POLYPROPYLENE VENTING SYSTEM ULC-S636
PolyPro by Duravent
IMPORTANT
ML193DF exhaust and intake connections are made
of PVC. Use PVC primer and solvent cement when
using PVC vent pipe. When using ABS vent pipe, use
transitional solvent cement to make connections to
the PVC fittings in the unit.
Use PVC primer and solvent cement or ABS solvent ce
ment meeting ASTM specifications, refer to Table 11. As
an alternate, use all purpose cement, to bond ABS, PVC, or
CPVC pipe when using fittings and pipe made of the same
materials. Use transition solvent cement when bonding
ABS to either PVC or CPVC.
Low temperature solvent cement is recommended during
cooler weather. Metal or plastic strapping may be used for
vent pipe hangers. Uniformly apply a liberal coat of PVC
primer for PVC or use a clean dry cloth for ABS to clean in
side socket surface of fitting and male end of pipe to depth
of fitting socket.
Canadian Applications Only - Pipe, fittings, primer and
solvent cement used to vent (exhaust) this appliance must
be certified to ULC S636 and supplied by a single
manufacturer as part of an approved vent (exhaust) sys
tem. In addition, the first three feet of vent pipe from the fur
nace flue collar must be accessible for inspection.

Page 19
TABLE 12
OUTDOOR TERMINATION USAGE*
Input Size
Vent
Pipe
Dia. in.
STANDARD CONCENTRIC
Flush
Mount
Kit
Wall Kit Wall Ring Kit
Field
Fabricated
1-1/2 inch 2 inch 3 inch
2 inch 3 inch 2 inch
51W11
(US)
51W12
(CA)
22G44 (US)
430G28 (CA)
44J40
(US)
481J20 (CA)
15F74
71M80
(US)
444W92
(CA)
69M29
(US)
444W92
(CA)
60L46 (US)
444W93 (CA)
045
23YES YES 1YES 1YES 5YES 2YES
2-1/2 3YES YES 1YES 1YES 5YES 2YES
33YES YES 1YES 1YES 5YES 2YES
070
23YES YES 1YES 1YES 5YES 2YES
2-1/2 3YES YES 1YES 1YES 5YES 2YES
33YES YES 1YES 1YES 5YES 2YES
090
23YES YES YES 5YES YES YES
2-1/2 3YES YES YES 5YES YES YES
33YES YES YES 5YES YES YES
110
2 YES YES YES 5YES YES YES
2-1/2 YES YES 5YES YES YES
3 YES YES 5YES YES YES
NOTE - Standard Terminations do not include any vent pipe or elbows external to the structure. Any vent pipe or elbows external to the structure must be included in total vent length
calculations. See vent length tables.
* Kits must be properly installed according to kit instructions.
1Requires field-provided outdoor 1-1/2” exhaust accelerator.
2Concentric kits 71M80 and 44W92 include 1-1/2” outdoor accelerator, when used with 045 and 070 input models.
3Flush mount kit 51W11 and 51W12 includes 1-1/2 in. outdoor exhaust accelerator, required when used with 045, 070 and 090 input models.
4Termination kits 30G28, 44W92, 4493 and 81J20 are certified to ULC S636 for use in Canada only.
5See table 17 for vent accelerator requirements.

Page 20
Joint Cementing Procedure
All cementing of joints should be done according to the
specifications outlined in ASTM D 2855.
NOTE - A sheet metal screw may be used to secure the
intake pipe to the connector, if desired. Use a drill or
self tapping screw to make a pilot hole.
DANGER
DANGER OF EXPLOSION!
Fumes from PVC glue may ignite during system
check. Allow fumes to dissipate for at least 5 minutes
before placing unit into operation.
1 - Measure and cut vent pipe to desired length.
2 - Debur and chamfer end of pipe, removing any ridges
or rough edges. If end is not chamfered, edge of pipe
may remove cement from fitting socket and result in a
leaking joint.
3 - Clean and dry surfaces to be joined.
4 - Test fit joint and mark depth of fitting on outside of
pipe.
5 - Uniformly apply a liberal coat of PVC primer for PVC or
use a clean dry cloth for ABS to clean inside socket
surface of fitting and male end of pipe to depth of fitting
socket.
6 - Promptly apply solvent cement to end of pipe and in
side socket surface of fitting. Cement should be ap
plied lightly but uniformly to inside of socket. Take care
to keep excess cement out of socket. Apply second
coat to end of pipe.
NOTE - Time is critical at this stage. Do not allow prim
er to dry before applying cement.
7 - Immediately after applying last coat of cement to pipe,
and while both inside socket surface and end of pipe
are wet with cement, forcefully insert end of pipe into
socket until it bottoms out. Turn PVC pipe 1/4 turn dur
ing assembly (but not after pipe is fully inserted) to dis
tribute cement evenly. DO NOT turn ABS or cellular
core pipe.
NOTE - Assembly should be completed within 20 sec
onds after last application of cement. Hammer blows
should not be used when inserting pipe.
8 - After assembly, wipe excess cement from pipe at end
of fitting socket. A properly made joint will show a bead
around its entire perimeter. Any gaps may indicate an
improper assembly due to insufficient solvent.
9 - Handle joints carefully until completely set.
Venting Practices
FIGURE 18
* See table 11 for allowable pipe.
Piping Suspension Guidelines
NOTE - Isolate piping at the point where it exits the outside wall or
roof in order to prevent transmission of vibration to the structure.
SCHEDULE 40
PVC - 5'
all other pipe* - 3'
Wall
inside outside
24” maximum
3/4” minimum
Wall Thickness Guidelines
CHIMNEY
OR GAS
VENT
(Check sizing
for water
heater only)
FURNACE
(Replaced
by ML193)
WATER
HEATER
OPENINGS
(To Adjacent
Room)
If an ML193DF furnace replaces a furnace which was com
monly vented with another gas appliance, the size of the ex
isting vent pipe for that gas appliance must be checked.
Without the heat of the original furnace flue products, the
existing vent pipe is probably oversized for the single water
heater or other appliance. The vent should be checked for
proper draw with the remaining appliance.
FIGURE 19
REPLACING FURNACE THAT
WAS PART OF A COMMON
VENT SYSTEM