E 2003 Lennox Industries Inc.
Dallas, Texas, USA
504,666M
08/03
G51MP
SERIES
GAS FURNACE
Litho U.S.A.
WARNING
FIRE OR EXPLOSION HAZARD.
Failure to follow safety warnings exactĆ
ly could result in serious injury, death,
or property damage.
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 apĆ
pliance.
D Do not try to light any appliance.
D Do not touch any electrical switch; do not
use any phone in your building.
D Leave the building immediately.
D Immediately call your gas supplier from a
neighbor's phone. Follow the gas supplier's
instructions.
Installation and service must be
performed by a qualified installer,
service agency or the gas supplier.
D If you cannot reach your gas supplier, call
the fire department.
08/03
504,666M
*P504666M*
*2P0803*
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WARNING
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.
Do not use this furnace if any part has been underĆ
water. A flood-damaged furnace is extremely danĆ
gerous. Attempts to use the furnace can result in
fire or explosion. Immediately call a qualified serĆ
vice technician to inspect the furnace and to replace
all gascontrols, controlsystemparts, andelectrical
parts that have been wet or to replace the furnace,
if deemed necessary.
Your furnace is a gas appliance. It is critical that the gas
supplied to the unit be completely burned to avoid the proĆ
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.
IMPORTANT
Any additions, changes, or conversions required in
order for the appliance to satisfactorily meet the apĆ
plication needs must be made by a Lennox service
technician using factory specified and approved
parts.
WARNING
Carbon monoxide gas is invisible, odorless and
toxic.
Exposure to carbon monoxide gas can cause personal injuĆ
ry and even death to all occupants, including pets. Any item
that is powered by or gives off heat from a combustion proĆ
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 monoxĆ
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.
WARNING
Improper installation, adjustment, alteration, service
or maintenance can cause property damage, personĆ
al injury or loss of life. Installation and service must
be performed by a qualified installer, service agency
or the gas supplier.
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 maĆ
terial may be combustible.
Your furnace is designed to meet standards set by nationĆ
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 opĆ
erating environment. It is your responsibility to ensure that
this appliance is maintained. Proper maintenance is critiĆ
cal for your safety and the satisfactory operation of the
product. Lennox strongly recommends annual inĆ
spection and maintenance of this appliance. Contact
your Lennox dealer for an inspection by a qualified service
technician.
2 - 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 clearĆ
ances surrounding the furnace.
3 - DO NOT store chlorine or fluorine products near unit
or introduce these products into the combustion air.
These products can cause furnace corrosion.
Lighting Information & Operation
4 - DO NOT draw return air from a room where this furĆ
nace, or any other gas appliance (ie., a water heatĆ
er), is installed. When return air is drawn from a room,
a negative pressure is created in the room. If a gas apĆ
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
If you do not follow these instructions exactly, a fire
or explosion may result causing property damage,
personal injury or death.
BEFORE LIGHTING the unit, smell all around the apĆ
pliance area for gas. Be sure to smell next to the floor beĆ
cause some gas is heavier than air and will settle on the
floor.
Page 3
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The gas valve on the G51MP may be equipped with eiĆ
ther a gas control knob or gas control lever. Use only your
hand to push the lever or turn the gas control knob. Never
use tools. If the the lever will not move or the knob will not
push in or turn by hand, do not try to repair it. Call a qualiĆ
fied service technician. Force or attempted repair may
result in a fire or explosion.
White Rodgers 36G Series Gas Valve
INLET
PRESSURE
POST
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
OUTLET
PRESSURE
POST
Placing the G51MP furnace into operation:
®
G51MP units are equipped with a SureLight ignition
GAS VALVE SHOWN IN OFF POSITION
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
FIGURE 3
Honeywell VR8205 Series Gas Valve
®
MANIFOLD
MANIFOLD
PRESSURE
OUTLET
hot when there is no call for heat on units with SureLight
PRESSURE
ADJUSTMENT
SCREW
ignition system.
Operating the Gas Valve (Figures 3 and 4)
1 - STOP! Read the safety information at the beginning of
ON
this section.
2 - Set the thermostat to the lowest setting. See figure 2.
3 - Turn off all electrical power to the unit.
OFF
GAS VALVE SHOWN IN OFF POSITION
FIGURE 4
THERMOSTATS
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 service techĆ
nician or gas supplier.
FIGURE 2
Turning Off Gas 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.
1 - Set the thermostat to the lowest setting.
2 - Turn off all electrical power to the unit if service is to be
performed.
5 - Remove the upper access panel.
3 - Remove the upper access panel.
6 - White Rodgers 36G Gas Valve - Switch gas valve leĆ
ver to OFF.
Honeywell VR8205 Gas Valve - Turn knob on gas
4 - White Rodgers 36G Gas Valve - Switch gas valve leĆ
ver to OFF.
Honeywell VR8205 Gas Valve - Turn knob on gas
valve clockwise
4.
to OFF. Do not force. See figure
valve clockwise
to OFF. Do not force.
5 - Replace the upper access panel.
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 instrucĆ
tions. If you do not smell gas go to next step.
Filters
All G51MP filters are installed external to the unit. Filters
should be inspected monthly. Clean or replace the filters
when necessary to ensure proper furnace operation. ReĆ
placement filters must be rated for high velocity airflow.
Table 1 lists recommended filter sizes.
8 - White Rodgers 36G Gas Valve - Switch gas valve lever
to ON. See figure 3 for the White Rodgers 36G valve.
Honeywell VR8205 Gas Valve - Turn knob on gas valve
counterclockwise
to ON. Do not force.
A filter must be in place whenever the unit is operating.
Page 4
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TABLE 1
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.
Filter Size
Furnace
Cabinet Size
Side Return
16 X 25 X 1 (1)
16 X 25 X 1 (1)
16 X 25 X 1 (2)
Bottom Return
16 X 25 X 1 (1)
20 X 25 X 1 (1)
24 X 25 X 1 (1)
17-1/2"
21"
Vent pipe must be clear and free of obstructions and must
slope upward away from the furnace.
24-1/2"
Inspect the furnace return air duct connection to ensure
duct is sealed to the furnace and terminates outside the
space containing the furnace.
Maintenance
A qualified service technician should inspect the complete
system each season (heating and cooling). The following
maintenance procedures should only be conducted by a
qualified service technician. Do not attempt to service
the unit in any way.
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 and clean the condensate trap and drain.
During a seasonal check the service technician will inspect
the indoor blower, burner flames and electrical connections
along with the venting system.
WARNING
ELECTRICAL SHOCK, FIRE,
OR EXPLOSION HAZARD.
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.
Failure to follow safety warnings exactly could result
in dangerous operation, serious injury, death or
property damage.
Improper servicing could result in dangerous operaĆ
tion, serious injury, death, or property damage.
Before servicing, disconnect all electrical power to
furnace.
When servicing controls, label all wires prior to disĆ
connecting. Take care to reconnect wires correctly.
Verify proper operation after servicing.
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 injuĆ
ry or death.
Venting System
Burner Flame
WARNING
Asphyxiation Hazard
CAUTION
To ensure proper operation, a qualified technician
should annually check the burner flame.
The exhaust vent for this furnace 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 qualified service technician must annualĆ
ly inspect this furnace and its vent system.
Electrical
1 - Check all wiring for loose connections.
2 - Check for the correct voltage at the furnace (furnace
operating).
Annually (before heating season) inspect furnace venting
system, vent cap, heat exchanger, and burners for corroĆ
sion, deterioration, or deposits of debris. Remove any obĆ
structions.
3 - Check amp-draw on the blower motor.
Motor Nameplate__________Actual__________
Page 5
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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.
Service Reminder
Call your Lennox service technician if the unit will not operĆ
ate. Before calling, always check the following to be sure
service is required:
Planned Service
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.
You should expect a service technician to check the followĆ
ing items during an annual inspection. Power to the unit
must be shut off for the service technician's safety.
5 - Air filter should not be plugged, which will limit air flow.
6 - Is gas turned on at meter?
Fresh air grilles and louvers (on the unit and in the room
where the furnace is installed) - Must be open and unobĆ
structed to provide combustion air.
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.
Burners - Must be inspected for rust, dirt, or signs of water.
Vent pipe - Must be inspected for signs of water, damaged
or sagging pipe, or disconnected joints.
Serial Number __________________
Model Number __________________
Unit appearance - Must be inspected for rust, dirt, signs
of water, burnt or damaged wires, or components.
Safety Precautions
Blower access door - Must be properly in place and proĆ
vide a seal between the return air and the room where the
furnace is installed.
If you discover any of the following, shut down your
unit, and contact a Lennox dealer for an inspection by
a qualified technician.
Return air duct - Must be properly attached and provide
D If 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 unfaĆ
miliar noises.
an air seal to the unit.
Operating performance - Unit must be observed during
operation to monitor proper performance of the unit and the
vent system.
D If you smell any unusual odors, your unit may be operatĆ
ing improperly. For example, units can give off unfamilĆ
iar odors if components are required to operate in abĆ
normal conditions.
Combustion gases - Flue products must be analyzed and
compared to the unit specifications.
D Look for visible signs of a malfunctioning unit. Examples
include unusual amounts of condensate on windows inĆ
side your house, visibly burnt components or unusual
dirt or rust accumulations on the vent pipe or in the unit.
Problems detected during the inspection may make it necĆ
essary to temporarily shut down the furnace until the items
can be repaired or replaced.
D If you experience headache, nausea, fatigue, or dizziĆ
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 sympĆ
toms that are exaggerated at home, but seem to subĆ
side while you are away from the house, exposure to
carbon monoxide could be the cause.
Pay attention to your furnace. Situations can arise beĆ
tween annual furnace inspections that may result in unsafe
operation. For instance, items innocently stored next to the
furnace may obstruct the combustion air supply. This could
cause incomplete combustion and the production of carĆ
bon monoxide gas.
Page 6
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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: G51MP-24B-045-1.
Cabinet Parts
Upper access panel
Heating Parts
Flame Sensor
Blower access panel
Top Cap
Heat exchanger assembly
Gas manifold
Control Panel Parts
Combustion air inducer
Gas valve
Transformer
®
SureLight integrated control board
Main burner cluster
Main burner orifices
Pressure switches
Ignitor
Door interlock switch
Circuit Breaker
Blower Parts
Blower wheel
Primary limit control
Secondary limit
Motor
Motor mounting frame
Motor capacitor
Blower housing cutoff plate
Flame rollout switches
Combustion air inducer auxiliary limit
Page 7
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