Lennox SL297UHNV Series Guide

SL297UHNV
SERIES
Litho U.S.A.
507761-01
02/2018
Supersedes 11/2107
E2018 Lennox Industries Inc.
Dallas, Texas, USA
WHAT TO DO IF YOU SMELL GAS:
Do not store or use gasoline or other
flammable vapors and liquids in the
vicinity of this or any other ap
pliance.
Installation and service must be
performed by a qualified installer,
service agency or the gas supplier.
DDo not try to light any appliance.
DDo not touch any electrical switch; do not
use any phone in your building.
DImmediately call your gas supplier from a
neighbor's phone. Follow the gas supplier's
instructions.
DIf you cannot reach your gas supplier, call
the fire department.
DLeave the building immediately.
GAS FURNACE
FIRE OR EXPLOSION HAZARD.
Failure to follow safety warnings exact
ly could result in serious injury, death,
or property damage.
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.
WARNING

Page 2
SL297UHNV Parts Identification
EXCHANGER
ASSEMBLY
BLOWER
MOTOR
GAS VALVE
COMBUSTION AIR
INDUCER
FLUE
COLLAR
TOP CAP
INTEGRATED
CONTROL
PRESSURE SWITCH
ASSEMBLY
AIR INTAKE
ACCESS PANEL
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 problems associ
ated with a NO HEAT condition (frozen pipes, etc.)

Page 3
CAUTION
Before attempting to perform any maintenance, turn
the electrical power to unit OFF at the disconnect
switch.
NOTICE
Any additions, changes, or conversions required in
order for the appliance to satisfactorily meet the ap
plication needs must be made by a licensed profes
sional installer (or equivalent) using factory-speci
fied and approved parts.
Safety Instructions
1 - Keep the furnace area clear and free of combustible
material, gasoline, and other flammable vapors and
liquids. If it is installed in an insulated area, the furnace
must be kept free of insulating material. Insulating ma
terial may be combustible.
2 - After any heavy snow, ice or frozen fog event, the fur
nace 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 flow to unit. Unit must receive an
unobstructed flow 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 clear
ances surrounding the furnace.
4 - DO NOT store chlorine or fluorine 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 fur
nace, or any other gas appliance (ie., a water heat
er), is installed. When return air is drawn from a room,
a negative pressure is created in the room. If a gas ap
pliance is operating in a room with negative pressure,
the flue products can be pulled back down the vent
pipe and into the room. This reverse flow of the flue
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
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.
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 flow rate, adequate combustion, air, and proper
venting.
WARNING
Asphyxiation Hazard
Carbon monoxide gas is invisible, odorless and
toxic.
The exhaust vent for this furnace must be leak-free
and must be securely connected to the furnace flue
collar at all times.
For your safety and to fulfill the terms of the limited
warranty, a licensed professional service technician
(or equivalent) must annually inspect this furnace
and its vent system.
Exposure to carbon monoxide gas can cause personal inju
ry and even death to all occupants, including pets. Any item
that is powered by or gives off heat from a combustion pro
cess (including lawn mowers, automobiles, and fireplaces)
has the potential to produce carbon monoxide gas. Because
of this, Lennox recommends the use of a carbon monox
ide 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 safety.
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 criti
cal for your safety and the satisfactory operation of the
product. Lennox strongly recommends annual in
spection and maintenance of this appliance. Contact
your Lennox dealer for an inspection by a licensed profes
sional service technician (or equivalent).

Page 4
Start-Up & Operation Information
NOTE - When the furnace begins heating mode, the di
agnostic LED on the furnace control will display “H1”
for heating operation in 1st stage, or “H2” for heating
operation in 2nd stage. The LED can be seen through
the viewport on the lower access panel. See figure 2.
WARNING
If you do not follow these instructions exactly, a fire
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 floor because some gas is heavier than air and will
settle on the floor.
The gas valve on the SL297UHNV 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 re
pair may result in a fire or explosion.
FIGURE 2
FLAME
15 HSI/CAI
NEUTRALS
L1
ACC
HUM
14
3 6
P79
11 0
312
J2
47
W915
2 STAGE
COMPR
W951
HEAT
PUMP
W914
DEHUM
HARMONY
CUT FOR
OPTION
SELECTION
OUTDOOR SENSOR
DISCHARGE AIR SENSOR
12345 6
10 12
91 1 13
ON
ON
SureLight
®
W1W2 G Y2 Y1 CC DH LODS
R
W1 W2
G
Y2 Y1
C C
R
L
DH
78
14 15
SENSE
RI+ I−CR I+ I−C
OUTDOOR EQUIPMENT
I+ I−
INDOOR EQUIPMENT
IGN
CAI2
CAI1
N N
J3
S1
S4S3
DIAGNOSTIC
LED
Furnace Integrated Control
Placing the SL297UHNV furnace into operation:
SL297UHNV 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
automatically 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 3)
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 figure 3.
7 - Wait five minutes to clear out any gas. If you then smell
gas, STOP! Immediately call your gas supplier from a
neighbor's phone. Follow the gas supplier's instruc
tions. If you do not smell gas go to next step.
8 - Move switch on gas valve to ON. See figure 3.
FIGURE 3
GAS VALVE SHOWN IN THE ON POSITION
9 - Replace the upper access panel.
10 - Turn on all electrical power to 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
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.
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.
CAUTION
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.

Page 5
Filters
All SL297UHNV filters are installed external to the unit. Fil
ters should be inspected monthly. Clean or replace the fil
ter(s) when necessary to ensure proper furnace operation.
A filter must be in place when the unit is operating. See
table 1 for recommended filter sizes.
NOTE - Use replacement filters that are similar in size and
efficiency ratings to those originally provided by the in
stalling contractor. Use of replacement filters with higher fil
tration ratings may restrict air flow to the furnace. This may
result in reduced unit efficiency, as well as premature blow
er 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)
Maintenance
A licensed professional service technician (or equivalent)
should inspect the complete system each season (heating
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 maintenance could result in dangerous
operation, serious injury, death, or property damage.
Before performing maintenance disconnect all elec
trical power to furnace.
CAUTION
To ensure proper operation, a licensed professional
service technician (or equivalent) should check the
burner flame and conduct a combustion analysis
annually.
Annually (before heating season) inspect furnace venting
system, vent cap, heat exchanger, and burners for corro
sion, deterioration, or deposits of debris. Remove any ob
structions.
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 filled 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 flames, 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 access panel must be securely in place
when the blower and burners are operating. Gas
fumes, which could contain carbon monoxide, can
be drawn into living space resulting in personal inju
ry or death.
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__________
Service Reminder
Call your Lennox service technician if the unit will not oper
ate. 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 filter should not be plugged, which will limit air flow.
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 __________________

Page 6
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).
DIf you repeatedly hear any new or unfamiliar sounds
while your unit is operating, there may be a problem. For
example, poorly performing burners can produce unfa
miliar noises.
DIf you smell any unusual odors, your unit may be operat
ing improperly. For example, units can give off unfamil
iar odors if components are required to operate in ab
normal conditions.
DLook for visible signs of a malfunctioning unit. Examples
include unusual amounts of condensate on windows in
side your house, visibly burnt components or unusual
dirt or rust accumulations on the vent pipe or in the unit.
DIf you experience headache, nausea, fatigue, or dizzi
ness, the cause could be exposure to carbon monoxide
gas. This is often misdiagnosed as the flu because
symptoms are similar. If you suffer from flu-like symp
toms that are exaggerated at home, but seem to sub
side while you are away from the house, exposure to
carbon monoxide could be the cause.
WARNING
Do not use this furnace if any part has been under
water. A flood-damaged furnace is extremely dan
gerous. Attempts to use the furnace can result in
fire or explosion. Immediately call a licensed pro
fessional service technician (or equivalent) to in
spect 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 neces
sary.
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 qualified 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 tech
nician (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 ap
plicable.
3- Inspect all gas pipe and connections for leaks.
4- Check the cleanliness of filters 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 neces
sary.
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 in
stalled in the hoses remember to remove and clean be
fore reinstalling the hoses.
8- Evaluate the heat exchanger integrity by inspecting the
heat exchanger per the AHRI heat exchanger inspec
tion procedure. This procedure can be viewed at
www.ahrinet.org
9- Ensure sufficient combustion air is available to the fur
nace. Fresh air grilles and louvers (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 to
ward 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.
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 fur
nace inspection to ensure proper combustion and oper
ation. Consult Service Literature for proper combustion
values.
14 Verify operation of CO detectors and replace batteries
as required.

Page 7
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 flame sensor. Check microamps before and
after. Check controls and safety devices (gas valve,
flame sensor, temperature limits). Consult Service
Manual for proper operating range. Thermal Limits
should be checked by restricting airflow and not dis
connecting the indoor blower. For additional details,
please see Service and Application Note H049.
2 - Verify that system total static pressure and airflow set
tings are within specific operating parameters.
3 - Clock gas meter to ensure that the unit is operating at
the specified firing rate for each stage of operation.
Check the supply pressure and the manifold pressure
on both low fire and high fire. If manifold pressure ad
justment is necessary, consult the Service Literature
for unit specific information on adjusting gas pressure.
Not all gas valves are adjustable. Verify correct tem
perature rise.
CAUTION
As with any mechanical equipment, personal injury
can result from contact with sharp sheet metal
edges. Be careful when you handle this equipment.
Repair Parts List
The following repair parts are available through Lennox dealers. When ordering parts, include the complete furnace model
number listed on the CSA International nameplate -- Example: SL297UH040NV36B. All service must be done by a li
censed 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
Blower housing cutoff plate
Heating Parts
Flame Sensor
Heat exchanger assembly
Gas manifold
Combustion air inducer
Gas valve
Burner assembly
Pressure switch
Ignitor
Primary limit control
Rollout switches