Lennox ML193DF045P36B, ML193DF110P60C, ML193DF070P36B, ML193DF090P48C Unit Information
Corp. 1026-L5
Service Literature
Revised 03-2014
ML193DF SERIES UNITS
ML193DF series units are high-efficiency gas furnaces
manufactured with Lennox DuralokPlust aluminized 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.
ML193DF
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 1
© 2014 Lennox Industries Inc.
Litho U.S.A.
SPECIFICATIONS
Gas
Heating
Performance
Model No. ML193DF045P36B ML193DF070P36B ML193DF090P48C ML193DF110P60C
1
AFUE 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.)
3.5 / 10.0 3.5 / 10.0 3.5 / 10.0 3.5 / 10.0
Nat. Gas / LPG/Propane
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
Blower motor full load amps 6.1 6.1 8.2 11.5
Voltage 120 volts - 60 hertz - 1 phase
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 Efciency based on DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherized
furnaces.
Page 2
OPTIONAL ACCESSORIES - MUST BE ORDERED EXTRA
“B” Width Models “C” Width Models
CABINET ACCESSORIES
Downow 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
Downow 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 specic venting information.
Termination Kits Direct Vent Applications
Only
Termination Kits -
Direct or Non-Direct vent
Roof Termination Flashing Kit - Direct or Non-Direct Vent Contains two ashings
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 certied to ULC S636 standard for use in Canada 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
Wall - Close
Couple WTK
US - 2 in. 22G44 - - -
3 in. 44J40 44J40
Canada - 2 in. 30G28 - - -
3 in. 81J20 81J20
Roof 2 in. 15F75 15F75
Wall Ring Kit 2 in. 15F74
44J41 44J41
3
15F74
High Altitude
Input
Pressure Switch 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
GAS HEAT ACCESSORIES
Natural Gas to
LPG/Propane Kit
Page 3
LPG/Propane
to Natural Gas Kit
Natural Gas
High Altitude
Orice Kit
BLOWER DATA
ML193DF045XP36B PERFORMANCE (Less Filter)
External
Static
Pressure
in. w.g.
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
ML193DF070XP36B PERFORMANCE (Less Filter)
External
Static
Pressure
in. w.g.
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
Air Volume / Watts at Various Blower Speeds
High
cfm Watts cfm Watts cfm Watts cfm Watts
Air Volume / Watts at Various Blower Speeds
High
cfm Watts cfm Watts cfm Watts cfm Watts
Medium-
High
Medium-
High
Medium-
Low
Medium-
Low
Low
Low
ML193DF090XP48C PERFORMANCE (Less Filter)
External
Static
Pressure
in. w.g.
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
ML193DF110XP60C PERFORMANCE (Less Filter)
External
Static
Pressure
in. w.g.
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
Air Volume / Watts at Various Blower Speeds
High
cfm Watts cfm Watts cfm Watts cfm Watts
Air Volume / Watts at Various Blower Speeds
High
cfm Watts cfm Watts cfm Watts cfm Watts
Medium-
High
Medium-
High
Medium-
Low
Medium-
Low
Low
Low
Page 4
CONTROL BOX
(Includes integrated control,
transformer and door switch)
BLOWER MOTOR
BLOWER
ACCESS
PANEL
PARTS ARRANGEMENT
BAG ASSEMBLY
(hidden)
BURNER
ACCESS
PANEL
COMBUSTION
AIR INDUCER
BLOWER DECK
PRIMARY LIMIT
COLD END HEADER BOX
HEAT EXCHANGER
GAS VALVE
BURNER BOX ASSEMBLY
(includes sensor, rollout switches and ignitor)
FIGURE 1
Page 5
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.
ML193DF Control Box
INTEGRATED IGNITION
CONTROL
(A92)
DOOR INTERLOCK
SWITCH (S51)
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.
TRANSFORMER
(T1)
FIGURE 2
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)
TABLE 1
4-Pin Terminal Designation
PIN # FUNCTION
1 Combustion Air Inducer Line
2
3
4
Ignitor Line
Combustion Air Inducer Neutral
Ignitor Neutral
TABLE 2
12-Pin Terminal Designations
PIN # FUNCTION
1 High Limit Output
2 Not Used
3 24V Line
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
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.
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 (bypassed). Once the prove switch is determined to be open,
the combustion air inducer is energized. When the differen
Page 6
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.
FAN‐OFF TIME IN SECONDS
NO JUMPER
To adjust fan-off timing, reposition jumper across pins
to achieve desired setting.
FIGURE 3
LED 1
LED 2
INTEGRATED CONTROL
(Automatic Hot Surface Ignition System)
TERMINAL DESIGNATIONS
HUM
LINE
XFMR
EAC
COOL
HEAT
PARK
FLAME
NEUTRALS
3 AMP, 32 VAC FUSE
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)
BLOWER OFF
DELAY JUMPER
FIGURE 4
Page 7
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
FAST FLASH
SLOW FLASH ON
OFF SLOW FLASH
ALTERNATING
SLOW FLASH
SLOW FLASH OFF Flame sensed without gas valve energized.
ON SLOW FLASH Rollout switch open. OR: 12‐pin connector improperly attached.
SIMULTANEOUS
SLOW FLASH
SIMULTANEOUS
FAST FLASH
ALTERNATING
SLOW FLASH
Power on - Normal operation.
Also signaled during cooling and continuous fan.
Normal operation - signaled when heating demand initiated at thermostat.
Primary or secondary limit switch open. Limit must close within 3 minutes or unit
goes into 1 hour Watchguard.
Pressure prove switch open.
OR: Blocked inlet/exhaust vent;
OR: Pressure switch closed prior to activation of combustion air inducer.
Watchguard 1 hour -- burners failed to ignite or lost flame 5 times during single
heating demand.
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.
*4 Sec.Trial
for Ign.
**Blower “On”
Delay
End of
Heat Demand
5 SEC
Post
Purge
Blower
Off
Time
ON
OFF
DEMAND
CAI
IGNITOR
GAS VALVE
INDOOR BLOWER
*Ignitor will energize the first 3 seconds of the 4 second trial for ignition
**Blower on time will be 45 seconds after gas valve is energized. Blower off time will depend on “OFF TIME” Setting.
15 Sec.
Pre -Purge
20 sec.
Ignitor Warmup
FIGURE 5
Page 8
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 (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 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
1 Combustion Air Inducer Line
2
3
4
Ignitor Line
Combustion Air Inducer Neutral
Ignitor Neutral
TABLE 5
12-Pin Terminal Designations
PIN # FUNCTION
1 High Limit Output
2 Sensor
3 24V Line
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
TABLE 6
DIAGNOSTIC CODES
LED Status DESCRIPTION
LED Off
LED On Normal operation.
1 Flash
2 Flashes
3 Flashes
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
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.
No power to control or control harware
fault detected.
Flame present with gas vavle
de-energized.
Pressure switch closed with combustion
air inducer de-energized.
Pressure switch open with combus
tion air inducer energized.
Lockout, buners lost flame too many
times.
Page 9
LED
ЙЙЙЙЙЙЙЙЙ
INTEGRATED CONTROL
(Automatic Hot Surface Ignition System)
TERMINAL DESIGNATIONS
HUM
LINE
XFMR
EAC
COOL
HEAT
PARK
CONT
NEUTRALS
TWIN
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)
TWIN
ON
OFF
DEMAND
CAI
IGNITOR
GAS VALVE
INDOOR BLOWER
*Blower on time will be 30 seconds after flame is sensed. Blower off time will depend on “OFF TIME” Setting.
PUSH BUTTON
Pre -Purge Ignitor Warm-up
15
FIGURE 6
ELECTRONIC IGNITION
351
Trial for
Ignition
FIGURE 7
39
Blower “On”*
Delay
5 SEC69
Post
Purge
Page 10
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.
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.
HEAT FAN‐OFF TIME IN SECONDS
NO JUMPER
To adjust fan-off timing, reposition jumper across pins to
60 Second
off Time
60
90
120
180
achieve desired setting.
90 Second
off Time
60
90
120
180
120 Second
60
off Time
90
120
180
FIGURE 8
180 Second
off Time
60
90
120
180
Page 11
FIELD WIRING FOR TWINNING THE ML193DF
TWO-STAGE THERMOSTAT
R
Call For Cool
Y
Call For Fan
G
Call For 1st
Stage Heat
Call For 2nd
StageHeat
W1
W2
ISOLATION
RELAY
TWIN
TWIN
SINGLE STAGE THERMOSTAT
R
TWIN 1
Y
G
Call For Cool
Call For Fan
Call For Heat
R
Y
G
W
W
C
ISOLATION
RELAY
R
TWIN 2
Y
G
W
TWIN
TWIN
R
TWIN 1
Y
G
W
C
R
TWIN 2
Y
G
W
C
C
FIGURE 9
Page 12
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 leftmost 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 +
a temperature rise. All flame rollout switches are manual
reset.
12_F (121_C + 6.7_C) on
SENSOR
ML193DF Burner Box Assembly
IGNITOR
BURNERS
ROLLOUT SWITCHES
FRONT BURNER BOX PLATE
GAS VALVE
FIGURE 10
Page 13
IGNITOR CHECKS
TABLE 7
Control Ohms
103085
100973
39 to 70
24 to 47
Voltage +
120
95
10%
Multi−Meter
Test 1
(set to ohms)
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.
Integrated Control Detail
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.
Multi−Meter
(set to ohms)
Test 2
Integrated Control DetailIntegrated Control Detail
Multi−Meter
(set to VAC)
Test 3
Integrated Control 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. See
table 7. If voltage reads below these values, check for
correct supply voltage to furnace.
FIGURE 11
Page 14
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 deenergizes 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.
Primary Limit Location and Heat Exchanger
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
Burner Detail Top Vie
w
IGNITOR
Install limit face down
FIGURE 12
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
SENSOR
ORIFICES
FIGURE 13
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.
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
(under
barbed
fitting)
INLET
PRESSURE
PORT
Gas Valve
MANIFOLD
PRESSURE
OUTLET
PORT
FIGURE 14
Page 15
8. Combustion Air Inducer (B6)
& Cold End Header Box
Pressure Switch
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.
BRACKET
24VAC
TERMINALS
TAP
TAP
FIGURE 15
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
Altitude ft
ML193DF
0 - 4500
4501 -
7500
7501 - 10000
Set Point SetPoint Set Point
-045
-070
-090
-110
-0.65 -0.60 -0.55
*Set point is factory set and non-adjustable
Page 16
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