Lennox ML193UH045P36B, ML193UH070P36B, ML193UH070P24B, ML193UH090P36C, ML193UH090P48C Unit Information

Corp. 1025-L5

Service Literature

Revised 03-2014

ML193UH SERIES UNITS

ML193UH series units are high-efficiency gas furnaces
manufactured with Lennox DuralokPlust aluminized steel
clamshell-type heat exchangers, with a stainless steel con
densing coil. ML193UH units are available in heating input
capacities of 44,000 to 132,000 Btuh (13 to 38.6 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 ML193UH
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.

ML193UH

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 7............................

II Placement and Installation 19....................

III-Start-Up 40...................................

IV-Heating System Service Checks 41..............

V-Typical Operating Conditions 43.................

VI-Maintenance 44...............................

VII-Sequence of Operation and Flow Charts 47......

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

Temperature rise range - °F 25 - 55 50 - 80 40 - 70 50 - 80

Gas Manifold Pressure (in. w.g.)

Nat. Gas / LPG/Propane

High static - in. w.g. 0.50 0.50 0.50 0.50

Connections

Intake / Exhaust Pipe (PVC) 2 / 2 2 / 2 2 / 2 2 / 2

in.

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

Wheel nom. dia. x width - in. 10 x 8 10 x 8 10 x 8 10 x 8

Blower

Tons of add-on cooling 2.5 - 3 1.5 - 2 2.5 - 3 2 - 3

Air Volume Range - cfm 700 - 1600 390 - 1140 660 - 1615 695 - 1620

Electrical
Data

Blower motor full load amps 6.1 3.1 6.1 6.1

Maximum overcurrent protection 15 15 15 15

Shipping Data lbs. - 1 package 122 125 127 143

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.

Model No. ML193UH045P36B ML193UH070P24B ML193UH070P36B ML193UH090P36C

1

AFUE 93% 93% 93% 93%

Input - Btuh 44,000 66,000 66,000 88,000

Output - Btuh 42,000 62,000 62,000 83,000

3.5 / 10.0 3.5 / 10.0 3.5 / 10.0 3.5 / 10.0

Gas pipe size IPS 1/2 1/2 1/2 1/2

Motor output - hp 1/3 1/5 1/3 1/3

Voltage 120 volts - 60 hertz - 1 phase

SPECIFICATIONS

Gas
Heating
Performance

Temperature rise range - °F 40 - 70 50 - 80 40 - 70 45 - 75

Gas Manifold Pressure (in. w.g.)

Nat. Gas / LPG/Propane

High static - in. w.g. 0.50 0.50 0.50 0.50

Connections

Intake / Exhaust Pipe (PVC) 2 / 2 2 / 2 2 / 2 2 / 2

in.

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

Wheel nom. dia. x width - in. 10 x 10 10 x 10 11 ½ x 10 11 ½ x 10

Blower

Tons of add-on cooling 3 - 4 3 - 4 4 - 5 4 - 5

Air Volume Range - cfm 900 - 2025 850 - 2030 1210 - 2525 1340 - 2800

Electrical
Data

Blower motor full load amps 8.2 8.2 11.5 11.5

Maximum overcurrent protection 15 15 15 15

Shipping Data lbs. - 1 package 146 155 161 178

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.

Model No. ML193UH090P48C ML193UH110P48C ML193UH110P60C ML193UH135P60D

1

AFUE 93% 93% 93% 93%

Input - Btuh 88,000 110,000 110,000 132,000

Output - Btuh 83,000 103,000 103,000 123,000

3.5 / 10.0 3.5 / 10.0 3.5 / 10.0 3.5 / 10.0

Gas pipe size IPS 1/2 1/2 1/2 1/2

Motor output - hp 1/2 1/2 1 1

Voltage 120 volts - 60 hertz - 1 phase

Page 2

OPTIONAL ACCESSORIES - MUST BE ORDERED EXTRA

“B” Width

Models

CABINET ACCESSORIES

Horizontal Suspension Kit - Horizontal only 51W10 51W10 51W10
Return Air Base - Upow only 50W98 50W99 51W00

CONDENSATE DRAIN KITS

Condensate Drain Heat Cable 6 ft. 26K68 26K68 26K68

24 ft. 26K69 26K69 26K69
50 ft. 26K70 26K70 26K70

Heat Cable Tape Fiberglass - 1/2 in. x 66 ft. 36G53 36G53 36G53

Aluminum foil - 2 in. x 60 ft. 16P89 16P89 16P89

Crawl Space Vent Drain Kit 51W18 51W18 51W18

CONTROLS

Twinning Kit 65W80 65W80 65W80

FILTER KITS

1

Air Filter and

Rack Kit

Horizontal (end) Size of lter - in. 87L96 - 18 x 25 x 1 87L97 - 20 x 25 x 1 87L98 - 25 x 25 x 1

Side Return Single 44J22 44J22 44J22

Ten Pack 66K63 66K63 66K63

Size of lter - in. 16 x 25 x 1 16 x 25 x 1 16 x 25 x 1

NIGHT SERVICE KITS

Night Service Kit 51W03 51W03 51W03

TERMINATION KITS

See Installation Instructions for specic venting information.

Termination Kits ­Direct Vent
Applications Only

Termination Kits ­Direct or Non­Direct vent
Roof Termination Flashing Kit - Direct or

Non-Direct Vent (2 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 certied to ULC S636 standard for use in Canada only.

Concentric US - 2 in. 71M80 69M29 - - -

3 in. - - - 60L46 60L46

Canada - 2 in. 44W92 44W92 - - -

3 in. - - - 44W93 44W93

Flush-Mount 2, 2-1/2 or 3 in. 51W11 51W11 51W11

Wall - Close

Couple

Wall - Close

Couple WTK

US - 2 in. 22G44 - - - - - -

3 in. 44J40 44J40 44J40

Canada - 2 in. 30G28 - - - - - -

3 in. 81J20 81J20 81J20

Roof 2 in. 15F75 15F75 - - -

Wall Ring Kit 2 in. 15F74

2 in. 44J41 44J41 44J41

“C” Width

“D” Width

Models

3

15F74 - - -

Models

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

INSTALLATION CLEARANCES - INCHES (MM)

Top/Plenum 1 inch (25 mm)

Front (service/alcove) 24 inches (610 mm)

NOTE − Air for combustion must conform to the methods outlined in the National Fuel Gas Code (NFPA 54/ANSI−Z223.1)

or the National Standard of Canada CAN/CSA−B149.1 Natural Gas and Propane Installation Code”.

NOTE − In the U.S. ue sizing must conform to the methods outlined in the current National Fuel Gas Code (NFPA 54/

ANSI−Z223.1) or applicable provisions of local building codes. In Canada ue sizing must conform to the methods
outlined in National Standard of Canada CAN/CSA−B149.1.

1

Allow proper clearances to accommodate condensate trap and vent pipe installation.

2

Do not install the furnace directly on carpeting, tile, or other combustible materials other than wood ooring.

GAS HEAT ACCESSORIES

Natural Gas to

LPG/Propane Kit

Sides

1

0 inches (0 mm)

Rear 0 inches (0 mm)

Front 0 inches (0 mm)

2

Floor

Combustible

Page 3

LPG/Propane

to Natural Gas Kit

Natural Gas

High Altitude

Orice Kit

BLOWER DATA

ML193UH045P36B PERFORMANCE (Less Filter)

External

Static

Pressure

in. w.g.

0.00 1600 700 1370 590 1160 475 1005 400

0.10 1600 685 1355 565 1155 465 1015 390

0.20 1550 650 1330 540 1150 445 1000 380

0.30 1480 625 1295 515 1140 430 975 365

0.40 1425 590 1280 490 1105 415 975 350

0.50 1355 565 1190 460 1085 395 940 335

0.60 1320 545 1165 435 1030 375 900 315

0.70 1225 500 111 0 425 975 355 855 310

0.80 1135 480 1050 395 920 330 780 280

0.90 1025 445 950 360 800 295 700 255

ML193UH070P24B PERFORMANCE (Less Filter)

External

Static

Pressure

in. w.g.

0.00 1140 455 920 365 765 295 710 265

0.10 1135 445 900 360 765 290 690 255

0.20 1125 430 895 350 755 285 680 255

0.30 1090 415 870 340 725 280 660 250

0.40 1065 405 870 325 715 270 635 245

0.50 1020 390 825 315 675 260 605 235

0.60 945 365 780 300 640 250 555 225

0.70 910 350 740 295 585 240 505 220

0.80 790 325 670 275 510 225 455 205

0.90 735 310 575 255 460 220 390 195

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

ML193UH090P36C PERFORMANCE (Less Filter)

External

Static

Pressure

in. w.g.

0.00 1620 745 1340 620 1130 500 965 405

0.10 1610 720 1335 595 1135 490 975 395

0.20 1565 695 1335 565 1145 465 970 385

0.30 1525 665 1300 555 1135 455 970 370

0.40 1485 635 1295 520 1110 435 960 355

0.50 1431 600 1260 495 1090 405 940 345

0.60 1365 570 1210 475 1035 390 900 330

0.70 1295 535 1155 445 995 365 860 305

0.80 1200 505 1065 415 930 340 745 270

0.90 1060 460 955 375 820 305 695 260

ML193UH090P48C PERFORMANCE (Less Filter)

External

Static

Pressure

in. w.g.

0.00 2025 900 1690 780 1395 645 1200 540

0.10 1995 880 1705 760 1390 635 1205 525

0.20 1925 835 1675 715 1405 605 1205 505

0.30 1850 795 1640 680 1400 580 1170 490

0.40 1790 760 1575 645 1395 560 1170 475

0.50 1700 725 1540 625 1350 535 1140 450

0.60 1610 690 1455 580 1295 505 1100 430

0.70 1540 645 1365 550 1225 480 1030 405

0.80 1415 615 1265 510 1125 445 980 385

0.90 1270 565 1165 470 1060 420 900 350

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

ML193UH070P36B PERFORMANCE (Less Filter)

External

Static

Pressure

in. w.g.

0.00 1615 680 1355 570 1140 480 1030 400

0.10 1565 660 1365 545 1150 465 1020 385

0.20 1535 630 1340 525 1150 440 1025 375

0.30 1440 600 1300 500 1110 420 1000 350

0.40 1405 570 1255 470 1075 400 975 345

0.50 1340 535 1200 445 1045 380 945 330

0.60 1255 500 1125 420 995 355 875 310

0.70 1165 475 1080 395 935 335 820 290

0.80 1060 455 990 365 870 315 750 265

0.90 955 425 895 345 750 285 660 245

Air Volume / Watts at Various Blower Speeds

High

cfm Watts cfm Watts cfm Watts cfm Watts

Medium-

High

Medium-

Low

Low

ML193UH110P48C PERFORMANCE (Less Filter)

External

Static

Pressure

in. w.g.

0.00 2030 905 1750 805 1425 665 1225 530

0.10 1950 865 1755 770 1430 630 1215 515

0.20 1935 840 1675 735 1455 610 1230 505

0.30 1885 810 1660 685 1410 585 1200 485

0.40 1830 780 1585 645 1385 570 1190 470

0.50 1750 740 1565 630 1320 535 1165 455

0.60 1660 695 1485 585 1280 505 1105 425

0.70 1540 665 1380 555 1230 485 1060 405

0.80 1420 615 1290 520 1140 445 945 375

0.90 1290 575 1175 470 1045 410 850 350

Air Volume / Watts at Various Blower Speeds

High

cfm Watts cfm Watts cfm Watts cfm Watts

Medium-

High

Page 4

Medium-

Low

Low

BLOWER DATA

ML193UH110P60C PERFORMANCE (Less Filter)

Air Volume / Watts at Different Blower Speeds

External

Static

Pressure

in. w.g.

0.00 2525 1560 2175 1165 1820 905 1465 725 2520 1545 2135 1150 1750 905 1445 720

0.10 2585 1545 2200 1135 1860 900 1475 710 2555 1545 2135 1115 1775 890 1470 715

0.20 2515 1505 2150 1110 1840 890 1490 705 2465 1480 2105 1085 1775 875 1465 705

0.30 2445 1445 2135 1065 1790 870 1500 690 2370 1430 2045 1055 1750 855 1460 690

0.40 2340 1385 2065 1035 1770 845 1500 675 2275 1375 1990 1010 1730 830 1460 680

0.50 2230 1350 1985 985 1755 810

0.60 2130 1295 1920 950 1685 785 1425 640 2060 1290 1850 935 1650 780 1420 635

0.70 2030 1250 1815 905 1640 760 1405 625 1930 1230 1760 900 1580 750 1355 610

0.80 1920 1190 1735 865 1560 725 1350 605 1825 1180 1660 855 1505 710 1290 585

0.90 1735 1135 1620 830 1450 685 1270 575 1665 1130 1520 810 1415 675 1210 560

ML193UH135P60D PERFORMANCE (Less Filter)

External

Static

Pressure

in. w.g.

0.00 2800 1715 2155 1160 1730 900 1375 695 2720 1685 2110 1135 1670 905 1355 705

0.10 2770 1665 2170 1145 1740 895 1415 700 2660 1650 2110 1115 1725 895 1390 700

0.20 2690 1635 2150 1110 1770 890 1450 700 2600 1585 2125 1090 1750 885 1450 695

0.30 2590 1560 2140 1080 1785 870 1455 695 2535 1525 2075 1065 1750 865 1465 685

0.40 2500 1535 2105 1055 1785 855 1475 690 2400 1490 2055 1030 1715 845 1460 680

0.50 2420 1465 2050 1025 1770 835

0.60 2330 1410 2015 995 1720 810 1460 655 2270 1385 1950 970 1720 800 1445 650

0.70 2225 1370 1965 960 1690 785 1450 650 2175 1335 1895 950 1665 780 1430 635

0.80 2150 1335 1875 925 1655 755 1435 630 2075 1295 1840 910 1605 745 1400 620

0.90 2025 1290 1830 890 1575 720 1375 605 1975 1255 1755 875 1540 725 1340 590

Bottom Return Air, Side Return Air with Optional Return
Air Base, Return Air from Both Sides or Return Air from
Bottom and One Side.

High Medium-High Medium-Low Low High Medium-High Medium-Low Low

cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts

1470 665 2185 1345 1930 970 1690 800 1460 655

Air Volume / Watts at Different Blower Speeds
Bottom Return Air, Side Return Air with Optional Return
Air Base, Return Air from Both Sides or Return Air from
Bottom and One Side.

High Medium-High Medium-Low Low High Medium-High Medium-Low Low

cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts cfm Watts

1465 665 2335 1420 2000 1005 1725 825 1455 660

Single Side Return Air − Air volumes in bold require eld

fabricated transition to accommodate 20 x 25 x 1 in. air lter
in order to maintain proper air velocity.

Single Side Return Air − Air volumes in bold require eld
fabricated transition to accommodate 20 x 25 x 1 in. air lter
in order to maintain proper air velocity.

Page 5

ML193UH PARTS IDENTIFICATION

FLEXIBLE NO-HUB
EXHAUST COLLAR

MANIFOLD

GAS VALVE

FLUE COLLAR

COMBUSTION AIR

INDUCER

BURNER
ACCESS

PANEL

BURNER BOX

ASSEMBLY

COMBUSTION

AIR PRESSURE

SWITCH

DuralokPlus

HEAT EXCHANGER

ASSEMBLY

TM

TOP CAP

PRIMARY LIMIT

CABINET

BAG ASSEMBLIES

(shipping location)

SIGHT
GLASS

BLOWER

ACCESS

DOOR

COLD END

HEADER BOX

BLOWER

ASSEMBLY

CONTROL BOX

(includes integrated control, transformer and interlock switch)

FIGURE 1

Page 6

I-UNIT COMPONENTS

ML193UH 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.

ML193UH Control Box

TRANSFORMER

(T1)

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 flame sensor (figure

10). 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 two LED lights (DS1 red
and DS2 green) for troubleshooting and two accessory ter
minals rated at (1) one amp. The integrated control also
features 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.

INTEGRATED IGNITION

CONTROL

(A92)

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 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 during after which the gas valve opens sec
onds for a 4-second trial for ignition. The ignitor remains
energized for the first 3 seconds during the 4 second trial. If
ignition is not proved during the 4-second period, the inte
grated control will try four more times with an inter purge
and warm-up time between trials of 35 seconds. After a to
tal of five trials for ignition (including the initial trial), the inte
grated control goes into Watchguard-Flame Failure mode.
After a 60-minute reset period, the integrated control will
begin the ignition sequence again.
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 8

The integrated control is equipped with two LED lights for troubleshooting. The diagnostic codes are listed below in table 3.

ЙЙЙЙЙЙЙЙЙ

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 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 nitirde 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 during
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 (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.

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 10

LED

ЙЙЙЙЙЙЙЙЙЙЙЙЙЙЙЙЙЙЙЙЙЙЙЙ

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 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 1 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 ML193UH 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

off Time

60

90

120

180

FIGURE 8

180 Second

off Time

60

90

120

180

Page 12

FIELD WIRING FOR TWINNING THE ML193UH

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 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)

ML193UH 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 front burner box plate
and the tip protrudes into the flame envelope of the left­most burner. The sensor can be removed for service with

ML193UH Burner Box Assembly

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 ML193UH 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 ML193UH units is
factory preset to open at 210_F +
temperature rise. All flame rollout switches are manual re
set.

12_F (99_C + 6.7_C) on a

FRONT BURNER BOX PLATE

ROLLOUT SWITCHES

FLAME SENSOR

BURNERS

IGNITOR

ORIFICES

GAS VALVE

FIGURE 10

Page 14

Check ignitor circuit for correct resistance.

Test 1

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 1

IGNITOR CHECKS

TABLE 7

Control Ohms

103085

100973

39 to 70
24 to 47

Voltage +

120

95

10%

Check ignitor for correct resistance.

Test 2

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 2

Multi−Meter

(set to ohms)

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.

Integrated Control Detail

Integrated Control Detail

Multi−Meter

(set to VAC)

Test 3

Integrated Control Detail

FIGURE 11

Page 15

4. Primary Limit Control (Figure 12)

Primary limit (S10) used on ML193UH 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, remove mounting screws,
rotate limit switch 90 degrees and 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 0.0340

Burner Detail Top View

IGNITOR

Install limit face down

FIGURE 12

5. Heat Exchanger (Figure 12)

ML193UH 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

FLAME SENSOR

ORIFICES

FIGURE 13

7. Gas Valve (GV1)

The ML193UH uses an internally redundant 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

INLET

PRESSURE

PORT

Gas Valve

MANIFOLD

PRESSURE

OUTLET

PORT

FIGURE 14

Page 16

8. Combustion Air Inducer (B6)
& Cold End Header Box

All ML193UH units use a combustion air inducer to move
air through the burners and heat exchanger during heating
operation. The blower uses a shaded pole 120VAC motor.
The motor operates during all heating operation and is con
trolled by integrated control A3. Blower operates continu
ously while there is a call for heat. The integrated control
will not proceed with the ignition sequence until combus
tion air inducer operation is sensed by the proving
switches.

The combustion air inducer 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 inducer creates negative pres
sure at unit start up. The channel contains an orifice used to
regulate flow created by the combustion air inducer. The
box has pressure taps for the combustion air inducer pres
sure switch hoses. The pressure switch measures the
pressure across the combustion air inducer orifice or differ
ence in the channel and the box. If replacement is neces

sary the gaskets used to seal the box to the vestibule
panel and the combustion air inducer to the box, must
also be replaced.

TABLE 9

ML193UH Unit

-045 0.563

-070 0.844

-090 1.00

-110 1.22

-135 1.30

Combustion Air Inducer

Orifice Size

9. Combustion Air Pressure Switch
(Figure 15)

ML193UH series units are equipped with a differential
pressure switch located on the cold end header box. The
switch monitors across the combustion air inducer 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.

Pressure Switch

FIGURE 15

On start‐up, the switch monitors whether the combustion
air inducer is operating. It closes a circuit to the integrated
control when the difference in pressure across the com
bustion air inducer orifice exceeds a non-adjustable factory
setting. If the switch does not successfully sense the re
quired 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 dif
ferential and opens the circuit to the integrated control. If
the condensate line is blocked, water will back up into the
header box and reduce the pressure differential across the
switch. The prove switch opens if the differential drops be
low 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.

Unit

-045

-070

-090

-110

-135

*Set point is factory set and non-adjustable

0 - 4500 4501 - 7500 7501 - 10000

Set Point

“w.c.

-0.65 -0.60 -0.55

Set Point “w.c

Set Point

“w.c.

Page 17