Lenoxx 2P0803 Guide

08/03
*2P0803*
504,666M
*P504666M*
G51MP
SERIES
Litho U.S.A.
504,666M
08/03
E 2003 Lennox Industries Inc.
Dallas, Texas, US

WHAT TO DO IF YOU SMELL GAS:
Do not store or use asoline or other
flammable vapors and liquids in the
vicinity of this or any other apĆ
pliance.
Installation and service must be
performed by a qualified installer,
service a ency or the as supplier.
DDo not try to li ht any appliance.
DDo not touch any electrical switch; do not
use any phone in your buildin .
DImmediately call your as supplier from a
nei hbor's phone. Follow the as supplier's
instructions.
DIf you cannot reach your as supplier, call
the fire department.
FIRE OR EXPLOSION HAZARD.
Failure to follow safety warnin s exactĆ
ly could result in serious injury, death,
or property dama e.
WARNING
DLeave the buildin immediately.
GAS FURNACE

Page 2
G51MP Parts Identification
DURALOKTM HEAT
EXCHANGER
ASSEMBLY
UPPER ACCESS
PANEL
BURNERS
BLOWER
MOTOR
CABINET
CONTROL BOX
GAS VALVE AND
MANIFOLD
COMBUSTION AIR
PROVING
(PRESSURE)
SWITCH
COMBUSTION AIR
INDUCER
BLOWER ACCESS
PANEL
FLUE
COLLAR
TOP CAP
SURELIGHTt
CONTROL BOARD
FIGURE 1
WARNING
Product contains fiber lass wool.
Disturbin the insulation in this product durin
installation, maintenance, or repair will expose you
to fiber lass wool. Breathin this may cause lun
cancer. (Fiber lass wool is known to the State of CalĆ
ifornia to cause cancer.)
Fiber lass wool may also cause respiratory, skin,
and eye irritation.
To reduce exposure to this substance or for further
information, consult material safety data sheets
available from address shown below, or contact your
supervisor.
Lennox Industries Inc.
P.O. Box 799900
Dallas, TX 75379-9900
NOTE - This manual must be left with the equipment
user.
WARNING
Do not set thermostat below 60°F (16°C) in heatin
mode. Settin thermostat below 60°F (16°C) reduces
the number of heatin cycles. Dama e to the unit
may occur that is not covered by the warranty.
WARNING
If overheatin occurs or if as supply fails to shut off,
shut off the manual as valve to the furnace before
shuttin off electrical supply.
CAUTION
Before attemptin to perform any service or mainteĆ
nance, turn the electrical power to unit OFF at the
disconnect switch.

Page 3
WARNING
Do not use this furnace if any part has been underĆ
water. A flood-dama ed furnace is extremely danĆ
erous. 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 as controls, control system parts, and electrical
parts that have been wet or to replace the furnace,
if deemed necessary.
IMPORTANT
Any additions, chan es, or conversions required in
order for the appliance to satisfactorily meet the apĆ
plication needs must be made by a Lennox service
technician usin factory specified and approved
parts.
WARNING
Improper installation, adjustment, alteration, service
or maintenance can cause property dama e, personĆ
al injury or loss of life. Installation and service must
be performed by a qualified installer, service a ency
or the as 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.
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.
4 - DO NOT draw return air from a room where this furĆ
nace, or any other as 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
The blower door must be securely in place when the
blower and burners are operatin . Gas fumes, which
could contain carbon monoxide, can be drawn into
the livin space resultin in personal injury or death.
Your furnace is a as 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.
WARNING
Carbon monoxide as is invisible, odorless and
toxic.
Exposure to carbon monoxide gas can cause personal injuĆ
ry and even death to all occupants, including pets. ny 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 as
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 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 stron ly recommends annual inĆ
spection and maintenance of this appliance. Contact
your Lennox dealer for an inspection by a qualified service
technician.
Li htin Information & Operation
WARNING
If you do not follow these instructions exactly, a fire
or explosion may result causin property dama e,
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 4
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.
Placin the G51MP furnace into operation:
G51MP units are equipped with a SureLight® 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 SureLight®
ignition system.
Operatin the Gas Valve (Fi ures 3 and 4)
1 - STOP! Read the safety information at the beginning of
this section.
2 - Set the thermostat to the lowest setting. See figure 2.
3 - Turn off all electrical power to the unit.
THERMOSTATS
FIGURE 2
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 - White Rodgers 36G Gas Valve - Switch gas valve leĆ
ver to OFF.
Honeywell VR8205 Gas Valve - Turn knob on gas
valve clockwise to OFF. Do not force. See figure
4.
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.
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.
FIGURE 3
White Rod ers 36G Series Gas Valve
GAS VALVE SHOWN IN OFF POSITION
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
OUTLET
PRESSURE
POST
INLET
PRESSURE
POST
ON
OFF
Honeywell VR8205 Series Gas Valve
GAS VALVE SHOWN IN OFF POSITION
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
MANIFOLD
PRESSURE
OUTLET
FIGURE 4
9 - Replace the upper access panel.
10 - Turn on all electrical power to to the unit.
11 - Set the thermostat to desired setting.
NOT - 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.
Turnin 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 - White Rodgers 36G Gas Valve - Switch gas valve leĆ
ver to OFF.
Honeywell VR8205 Gas Valve - Turn knob on gas
valve clockwise to OFF. Do not force.
5 - Replace the upper access panel.
Filters
ll 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.
filter must be in place whenever the unit is operating.

Page 5
TABLE 1
Furnace Filter Size
Furnace
Cabinet 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 (2) 24 X 25 X 1 (1)
Maintenance
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.
WARNING
ELECTRICAL SHOCK, FIRE,
OR EXPLOSION HAZARD.
Failure to follow safety warnin s exactly could result
in dan erous operation, serious injury, death or
property dama e.
Improper servicin could result in dan erous operaĆ
tion, serious injury, death, or property dama e.
Before servicin , disconnect all electrical power to
furnace.
When servicin controls, label all wires prior to disĆ
connectin . Take care to reconnect wires correctly.
Verify proper operation after servicin .
Ventin System
WARNING
Asphyxiation Hazard
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.
nnually (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.
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 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.
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 operatin . Gas
fumes, which could contain carbon monoxide, can
be drawn into livin space resultin in personal injuĆ
ry or death.
Burner Flame
CAUTION
To ensure proper operation, a qualified technician
should annually check the burner flame.
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__________ ctual__________

Page 6
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:
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 - ir 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 __________________
Safety Precautions
If you discover any of the followin , shut down your
unit, and contact a Lennox dealer for an inspection by
a qualified technician.
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 unfaĆ
miliar noises.
DIf 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.
DLook 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.
DIf 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.
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
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.
Fresh air rilles and louvers (on the unit and in the room
where the furnace is installed) - Must be open and unobĆ
structed to provide combustion air.
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.
Unit appearance - Must be inspected for rust, dirt, signs
of water, burnt or damaged wires, or components.
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.
Return air duct - Must be properly attached and provide
an air seal to the unit.
Operatin performance - Unit must be observed during
operation to monitor proper performance of the unit and the
vent system.
Combustion ases - Flue products must be analyzed and
compared to the unit specifications.
Problems detected during the inspection may make it necĆ
essary to temporarily shut down the furnace until the items
can be repaired or replaced.
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 7
Repair Parts List
The following repair parts are available through Lennox dealers. When ordering parts, include the complete furnace model
number listed on the CS International nameplate -- Example: G51MP-24B-045-1.
Cabinet Parts
Upper access panel
Blower access panel
Top Cap
Control Panel Parts
Transformer
SureLight® integrated control board
Door interlock switch
Circuit Breaker
Blower Parts
Blower wheel
Motor
Motor mounting frame
Motor capacitor
Blower housing cutoff plate
Heatin Parts
Flame Sensor
Heat exchanger assembly
Gas manifold
Combustion air inducer
Gas valve
Main burner cluster
Main burner orifices
Pressure switches
Ignitor
Primary limit control
Secondary limit
Flame rollout switches
Combustion air inducer auxiliary limit