Lennox ML193UH Guide

©2017 Lennox Industries Inc.
Dallas, Texas, USA
506465-01
04/2017
Supersedes 03/2017
ML193UH
SERIES
GAS FURNACE
WARNING
Improper installation, adjustment, alteration, service
or maintenance can cause property damage, personal
injury or loss of life. Installation and service must be
performed by a licensed professional HVAC installer or
equivalent, service agency, or the gas supplier.
WARNING
FIRE OR EXPLOSION HAZARD.
Failure to follow safety warnings exactly
could result in serious injury, death, or
property damage.
Do not store or use gasoline or other ammable
vapors and liquids in the vicinity of this or any
other appliance.
Installation and service must be performed
by a qualied installer, service agency or the
gas supplier.
WHAT TO DO IF YOU SMELL GAS:
• Do not try to light any appliance.
• Do not touch any electrical switch; do not use any
phone in your building.
• Leave the building immediatly
• Immediately call your gas supplier from a neighbor’s
phone. Follow the gas supplier’s instructions.
• If you cannot reach your gas supplier, call the re
department.
USER’S INFORMATION
MANUAL

Page 2
ML193UH Parts Identication
FIGURE 1
NOTE - This manual is the property of the homeowner
and must be left with the equipment user.
Notice to Homeowner
This furnace is equipped with safety devices that protect
you and your property. If one or more of these devices is
activated, furnace operation will stop. If your home is left
unattended for an extended period of time, equipment op-
eration must be checked periodically.
If this is not possible, the water supply to the house should be
shut off and the pipes should be drained. This will prevent prob-
lems associated with a NO HEAT condition (frozen pipes, etc.)
CAUTION
Before attempting to perform any service or maintenance,
turn the electrical power to unit OFF at disconnect switch.
DURALOKTM
HEAT
EXCHANGER
ASSEMBLY
BURNERS
BLOWER
MOTOR
GAS VALVE AND
MANIFOLD
COMBUSTION AIR
INDUCER
FLUE
COLLAR
TOP CAP
INTEGRATED
CONTROL
PRESSURE SWITCH
ASSEMBLY
AIR INTAKE COLLAR
BLOWER ACCESS
PANEL
UPPER ACCESS
PANEL

Page 3
WARNING
Do not set thermostat below 60°F (16°C) in heating
mode. Setting thermostat below 60°F (16°C) reduces
the number of heating cycles. Damage to the unit may
occur that is not covered by the warranty.
WARNING
If overheating occurs or if gas supply fails to shut off,
shut off the manual gas valve to the furnace before
shutting off electrical supply.
WARNING
Do not use this furnace if any part has been underwater.
A ood-damaged furnace is extremely dangerous.
Attempts to use the furnace can result in re or
explosion. Immediately call a licensed professional
service technician (or equivalent) to inspect the furnace
and to replace all gas controls, control system parts,
and electrical parts that have been wet or to replace the
furnace, if deemed necessary.
.
NOTICE
Any additions, changes, or conversions required in order
for the appliance to satisfactorily meet the application
needs must be made by a licensed professional installer
(or equivalent) using factory-specied and approved
parts.
WARNING
Improper installation, adjustment, alteration, service
or maintenance can cause property damage, personal
injury or loss of life. Installation and service must be
performed by a licensed professional installer (or
equivalent), a service agency, or the gas supplier.
Safety Instructions
1 - Keep the furnace area clear and free of combustible
material, gasoline, and other ammable vapors
and liquids. If it is installed in an insulated area, the
furnace must be kept free of insulating material.
Insulating material may be combustible.
2 - After any heavy snow, ice or frozen fog event, the
furnace vent pipes may become restricted. Always
check the vent system and remove any snow or ice
that may be obstructing the plastic intake or exhaust
pipes.
3 - DO NOT obstruct air ow to unit. Unit must receive
an unobstructed ow of combustion and ventilating
air. DO NOT block or obstruct air openings on
the furnace or air openings to the area in which
the furnace is installed. Take care to maintain
established clearances surrounding the furnace.
4 - DO NOT store chlorine or uorine products near
unit or introduce these products into the combustion
air. These products can cause furnace corrosion.
5 - DO NOT draw return air from a room where this
furnace, or any other gas appliance (ie., a water
heater), is installed. When return air is drawn from a
room, a negative pressure is created in the room. If
a gas appliance is operating in a room with negative
pressure, the ue products can be pulled back down
the vent pipe and into the room. This reverse ow
of the ue gas may result in incomplete combustion
and the formation of carbon monoxide gas. This
toxic gas might then be distributed throughout the
house by the furnace duct system.
WARNING
Blower access panel must be securely in place when
blower and burners are operating. Gas fumes, which
could contain carbon monoxide, can be drawn into living
space resulting in personal injury or death.
WARNING
CARBON MONOXIDE POISONING HAZARD
Failure to follow instruction could result in severe personal
injury or death due to carbon monoxide poisoning, if
combustion products inltrate into the building.
Check that all openings in the outside wall around
the vent (and air intake) pipe(s) are sealed to prevent
inltration of combustion products into the building.
Check that furnace vent (and air intake) terminal(s) are
not obstructed in any way during all seasons.

Page 4
Your furnace is a gas appliance. It is critical that the gas
supplied to the unit be completely burned to avoid the pro-
duction of carbon monoxide gas. Complete combustion of
the gas requires, but is not limited to, correct gas pressure
and gas ow rate, adequate combustion, air, and proper
venting.
WARNING
Carbon monoxide gas is invisible, odorless and toxic.
Exposure to carbon monoxide gas can cause personal in-
jury and even death to all occupants, including pets. Any
item that is powered by or gives off heat from a combus-
tion process (including lawn mowers, automobiles, and
replaces) has the potential to produce carbon monoxide
gas. Because of this, Lennox recommends the use of
a carbon monoxide detector in your home, even if
you do not own gas appliances. Reliable detectors are
available at reasonable retail prices. Contact your Lennox
dealer for more details about this investment in your safe-
ty.
Your furnace is designed to meet standards set by nation-
al agencies, and to operate safely when properly installed
and maintained. However, the unit’s performance can be
greatly impacted by the individual installation and the op-
erating environment. It is your responsibility to ensure that
this appliance is maintained. Proper maintenance is crit-
ical for your safety and the satisfactory operation of the
product. Lennox strongly recommends annual inspec-
tion and maintenance of this appliance. Contact your
Lennox dealer for an inspection by a licensed professional
service technician (or equivalent).
DANGER
Danger of explosion.
There are circumstances in which odorant used with LP/
propane gas can lose its scent. In case of a leak, LP/
propane gas will settle close to the oor and may be
difcult to smell. An LP/propane leak detector should be
installed in all LP applications. Do not attempt to bleed
the gas lines of air. Call your local gas provider.
Start-Up & Operation Information
WARNING
If you do not follow these instructions exactly,
a re or explosion may result causing
property damage, personal injury or death.
BEFORE PLACING THE UNIT INTO OPERATION, smell
all around the appliance area for gas. Be sure to smell
next to the oor because some gas is heavier than air and
will settle on the oor.
The gas valve on the ML193UH will be equipped with a gas
control switch. Use only your hand to move the switch. Never
use tools. If the switch will not move by hand, do not try to
repair it. Call a licensed professional service technician (or
equivalent). Force or attempted repair may result in a re or
explosion.
Placing the ML193UH furnace into operation:
ML193UH units are equipped with an ignition system. Do not
attempt to manually light burners on this furnace.
Each time the thermostat calls for heat, the burners will auto-
matically light. The ignitor does not get hot when there is no
call for heat on units with this ignition system.
Operating the Gas Valve (Figure 2)
1 - STOP! Read the safety information at the beginning of
this section.
2 - Set the thermostat to the lowest setting.
3 - Turn off all electrical power to the unit.
4 - This furnace is equipped with an ignition device which
automatically lights the burners. Do not try to light the
burners by hand.
5 - Remove the upper access panel.
6 - Move switch on gas valve to OFF. See gure 2.
7 - Wait ve minutes to clear out any gas. If you then
smell gas, STOP! Immediately call your gas supplier
from a neighbor’s phone. Follow the gas supplier’s
instructions. If you do not smell gas go to next step.
8 - Move switch on gas valve to ON. See gure 2.
GAS VALVE SHOWN IN ON POSITION
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
MANIFOLD
PRESSURE
OUTLET
FIGURE 2
9 - Replace the upper access panel.
10 - Turn on all electrical power to the unit.
11 - Set the thermostat to desired setting.
NOTE - When unit is initially started, steps 1 through 11 may
need to be repeated to purge air from gas line.
12 - If the appliance will not operate, follow the section
“Turning Off Gas to the Unit” and call your licensed
professional service technician (or equivalent).
Turning Off Gas to the Unit
1 - Set the thermostat to the lowest setting.
2 - Turn off all electrical power to the unit if service is to be
performed.
3 - Remove the upper access panel.
4 - Move switch on gas valve OFF.
5 - Replace the upper access panel.

Page 5
Filters
All ML193UH lters are installed external to the unit. Fil-
ters should be inspected monthly. Clean or replace the
lter(s) when necessary to ensure proper furnace oper-
ation. A lter must be in place when the unit is operating.
See table 1 for recommended lter sizes.
NOTE - Use replacement lters that are similar in size
and efciency ratings to those originally provided by the
installing contractor. Use of replacement lters with higher
ltration ratings may restrict air ow to the furnace. This
may result in reduced unit efciency, as well as premature
blower motor failure.
TABLE 1
Furnace
Cabinet Width
Filter Size
Side Return Bottom Return
17-1/2” 16 X 25 X 1 (1) 16 X 25 X 1(1)
21” 16 X 25 X 1 (1) 20 X 25 X 1 (1)
24-1/2” 16 X 25 X 1 (1) 24 X 25 X 1 (1)
Maintenance
A licensed professional service technician (or equivalent)
should inspect the complete system each season (heat-
ing and cooling). The following maintenance procedures
should only be conducted by a licensed professional ser-
vice technician (or equivalent). Do not attempt to service
the unit in any way.
WARNING
ELECTRICAL SHOCK, FIRE,
OR EXPLOSION HAZARD.
Failure to follow safety warnings exactly
could result in dangerous operation, serious
injury, death or property damage.
Improper servicing could result in dangerous
operation, serious injury, death, or property
damage. Before servicing, disconnect all
electrical power to furnace.
When servicing controls, label all wires prior
to disconnecting. Take care to reconnect
wires correctly. Verify proper operation after
servicing.
Venting System
WARNING
Asphyxiation Hazard
The exhaust vent for this furnace must be leak-free and
must be securely connected to the furnace ue collar at
all times.
For your safety and to fulll the terms of the limited
warranty, a licensed professional service technician (or
equivalent) must annually inspect this furnace and its
vent system.
Annually (before heating season) inspect furnace venting
system, vent cap, heat exchanger, and burners for cor-
rosion, deterioration, or deposits of debris. Remove any
obstructions.
Inspect the furnace for obvious signs of deterioration.
Inspect the furnace venting system to make sure it is in
place, physically sound, and without holes, corrosion, or
blockage.
Vent pipe must be clear and free of obstructions and must
slope upward away from the furnace.
Inspect the furnace return air duct connection to ensure
duct is sealed to the furnace and terminates outside the
space containing the furnace.
Inspect the physical support of the furnace to guarantee
that it is sound without sagging, cracks or gaps around
base and it maintains seal between base and support.
Inspect the condensate drain and trap for leaks and
cracks. The drain and trap must also be cleaned and the
trap must be lled with water.
During a seasonal check the service technician will con-
duct a combustion analysis. The technician will also in-
spect the indoor blower, burner ames, electrical connec-
tions and the venting system.
Blower
Check the blower wheel for debris and clean if necessary.
The blower motors are prelubricated for extended bearing
life. No further lubrication is needed.
WARNING
The blower door must be securely in place when the
blower and burners are operating. Gas fumes, which
could contain carbon monoxide, can be drawn into the
living space resulting in personal injury or death.
Burner Flame
CAUTION
To ensure proper operation, a licensed professional
service technician (or equivalent) should check the
burner ame and conduct a combustion analysis
annually.
Electrical
1 - Check all wiring for loose connections.
2 - Check for the correct voltage at the furnace (furnace
operating).
3 - Check amp-draw on the blower motor
Motor Nameplate__________Actual__________

Page 6
Service Reminder
Call your Lennox service technician if the unit will not op-
erate. Before calling, always check the following to be
sure service is required:
1 - Check that electrical disconnect switches are ON.
2 - Check room thermostat for proper setting.
3 - Replace any blown fuses or reset circuit breakers.
4 - Gas valve should be ON.
5 - Air lter should not be plugged, which will limit air
ow.
6 - Is gas turned on at meter?
7 - Is manual main shut-off valve open?
Record the model and serial number of the furnace. These
numbers are on the unit nameplate, which is located on
the blower deck below the combustion air inducer.
Serial Number __________________
Model Number __________________
Safety Precautions
If you discover any of the following, shut down your
unit, and contact a Lennox dealer for an inspection by
a licensed professional service technician (or equiva-
lent).
• If you repeatedly hear any new or unfamiliar sounds
while your unit is operating, there may be a prob-
lem. For example, poorly performing burners can
produce unfamiliar noises.
• If you smell any unusual odors, your unit may be
operating improperly. For example, units can give
off unfamiliar odors if components are required to
operate in abnormal conditions.
• Look for visible signs of a malfunctioning unit. Ex-
amples include unusual amounts of condensate on
windows inside your house, visibly burnt compo-
nents or unusual dirt or rust accumulations on the
vent pipe or in the unit.
• If you experience headache, nausea, fatigue, or
dizziness, the cause could be exposure to carbon
monoxide gas. This is often misdiagnosed as the
u because symptoms are similar. If you suffer from
u-like symptoms that are exaggerated at home,
but seem to subside while you are away from the
house, exposure to carbon monoxide could be the
cause.
Your vigilance may pay off in early detection of a problem
before either personal injury or property damage occurs.
Do not hesitate to contact a qualied service technician as
an investment in your well being.
Planned Service
Annual Furnace Maintenance
At the beginning of each heating season, and to comply
with the Lennox Limited Warranty, your system should be
checked as follows by a licensed professional service
technician
(or equivalent).
1 - Check wiring for loose connections, voltage at
indoor unit and amperage of indoor motor.
2 - Check the condition of the belt and shaft bearings
if applicable.
3 - Inspect all gas pipe and connections for leaks.
4 - Check the cleanliness of lters and change if
necessary (monthly).
5 - Check the condition and cleanliness of burners and
heat exchanger and clean if necessary.
6 - Check the cleanliness of blower assembly and
clean the housing, blower wheel and blower motor
if necessary.
7 - Inspect the condensate drain and trap for leaks and
cracks. The drain and trap must also be cleaned
and the trap must be primed with water. Inspect the
rubber hoses connected to the pressure switches for
cracks or loose connections, replace as necessary.
Remove the rubber hoses from the cold end header
box and inspect for any blockage, clean as needed.
If strainers are installed in the hoses remember to
remove and clean before reinstalling the hoses.
8 - Evaluate the heat exchanger integrity by inspecting
the heat exchanger per the AHRI heat exchanger
inspection procedure. This procedure can be
viewed at www.ahrinet.org
9 - Ensure sufcient combustion air is available to the
furnace. Fresh air grilles and louvers (on the unit
and in the room where the furnace is installed)
must be properly sized, open and unobstructed to
provide combustion air.
10 - Inspect the furnace intake and exhaust pipes to
make sure they are in place, structurally sound,
without holes, blockage or leakage and the
exhaust pipe is sloped toward the furnace. Inspect
terminations to ensure they are free of obstructions
and are structurally sound. Inspect the furnace
return air duct connection to ensure the duct is
sealed to the furnace. Check for air leaks on supply
and return ducts and seal where necessary.
NOTE - After any heavy snow, ice or frozen fog event the
furnace vent pipes may become restricted. Always check
the vent system and remove any snow or ice that may be
obstructing the plastic intake or exhaust pipes.

Page 7
11 - Inspect the furnace return air duct connection to
ensure the duct is sealed to the furnace. Check for
air leaks on supply and return ducts and seal where
necessary.
12 - Check the condition of the furnace cabinet insulation
and repair if necessary.
13 - Perform a complete combustion analysis during the
furnace inspection to ensure proper combustion
and operation. Consult Service Literature for proper
combustion values.
14 - Verify operation of CO detectors and replace
batteries as required.
Perform a general system test. Turn on the furnace to
check operating functions such as the start-up and shut-
off operation.
1 - Check the operation of the ignition system, inspect
and clean ame sensor. Check microamps before
and after. Check controls and safety devices (gas
valve, ame sensor, temperature limits). Consult
Service Manual for proper operating range. Thermal
Limits should be checked by restricting airow and
not disconnecting the indoor blower. For additional
details, please see Service and Application Note
H049.
2 - Verify that system total static pressure and airow
settings are within specic operating parameters.
3 - Clock gas meter to ensure that the unit is operating
at the specied ring rate for each stage of
operation. Check the supply pressure and the
manifold pressure on both low re and high re. If
manifold pressure adjustment is necessary, consult
the Service Literature for unit specic information
on adjusting gas pressure. Not all gas valves are
adjustable. Verify correct temperature rise.
WARNING
This prodcut contains a chemical known to the State
of California to cause cancer, birth defects, or other
reproductive harm.
Repair Parts List
The following repair parts are available through Lennox
dealers. When ordering parts, include the complete fur-
nace model number listed on the CSA International name-
plate -- Example: ML193UH045P24B. All service must be
done by a licensed professional installer (or equivalent), a
service agency, or the gas supplier.
Cabinet Parts
Upper access panel
Blower access panel
Top Cap
Control Panel Parts
Transformer
Integrated control
Door interlock switch
Blower Parts
Blower wheel
Motor
Motor mounting frame
Motor capacitor
Blower housing cutoff plate
Heating Parts
Flame Sensor
Heat exchanger assembly
Gas manifold
Combustion air inducer
Gas valve
Main burner cluster
Main burner orices
Pressure switch
Ignitor
Primary limit control
Flame rollout switches