Lennox G50UHi Series Guide

07/03
*2P0703*
504,650M
*P504650M*
G50UHi
SERIES
Litho U.S.A.
504,650M
07/03
E 2003 Lennox Industries Inc.
Dallas, Texas, US

WHAT TO DO IF YOU SMELL GAS:
Do not store or use g soline or other
fl mm ble v pors nd liquids in the
vicinity of this or ny other pĆ
pli nce.
Inst ll tion nd service must be
performed by qu lified inst ller,
service gency or the g s supplier.
DDo not try to light ny ppli nce.
DDo not touch ny electric l switch; do not
use ny phone in your building.
DImmedi tely c ll your g s supplier from
neighbor's phone. Follow the g s supplier's
instructions.
DIf you c nnot re ch your g s supplier, c ll
the fire dep rtment.
FIRE OR EXPLOSION HAZARD.
F ilure to follow s fety w rnings ex ctĆ
ly could result in serious injury, de th,
or property d m ge.
WARNING
DLe ve the building immedi tely.
GAS FURNACE

Page 2
G50UHi P rts Identific tion
DURALOKTM HEAT
EXCHANGER
ASSEMBLY
UPPER ACCESS
PANEL
BURNERS
BLOWER
MOTOR
CABINET
CONTROL BOX
GAS VALVE AND
MANIFOLD
COMBUSTION AIR
INDUCER
BLOWER ACCESS
PANEL
FLUE
TRANSITION
TOP CAP
SURELIGHT®
CONTROL BOARD
FIGURE 1
BLOWER CONTROL
MODULE
WARNING
Product cont ins fibergl ss wool.
Disturbing the insul tion in this product during
inst ll tion, m inten nce, or rep ir will expose you
to fibergl ss wool. Bre thing this m y c use lung
c ncer. (Fibergl ss wool is known to the St te of C lĆ
iforni to c use c ncer.)
Fibergl ss wool m y lso c use respir tory, skin,
nd eye irrit tion.
To reduce exposure to this subst nce or for further
inform tion, consult m teri l s fety d t sheets
v il ble from ddress shown below, or cont ct your
supervisor.
Lennox Industries Inc.
P.O. Box 799900
D ll s, TX 75379-9900
NOTE - This manual must be left with the equipment
user.
WARNING
Do not set thermost t below 60°F (16°C) in he ting
mode. Setting thermost t below 60°F (16°C) reduces
the number of he ting cycles. D m ge to the unit
m y occur th t is not covered by the w rr nty.
WARNING
If overhe ting occurs or if g s supply f ils to shut off,
shut off the m nu l g s v lve to the furn ce before
shutting off electric l supply.
CAUTION
Before ttempting to perform ny service or m inteĆ
n nce, turn the electric l power to unit OFF t the
disconnect switch.

Page 3
WARNING
Do not use this furn ce if ny p rt h s been underĆ
w ter. A flood-d m ged furn ce is extremely d nĆ
gerous. Attempts to use the furn ce c n result in
fire or explosion. Immedi tely c ll qu lified serĆ
vice technici n to inspect the furn ce nd to repl ce
ll g s controls, control system p rts, nd electric l
p rts th t h ve been wet or to repl ce the furn ce,
if deemed necess ry.
IMPORTANT
Any dditions, ch nges, or conversions required in
order for the ppli nce to s tisf ctorily meet the pĆ
plic tion needs must be m de by Lennox service
technici n using f ctory specified nd pproved
p rts.
WARNING
Improper inst ll tion, djustment, lter tion, service
or m inten nce c n c use property d m ge, personĆ
l injury or loss of life. Inst ll tion nd service must
be performed by qu lified inst ller, service gency
or the g s supplier.
S fety 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 dr w return ir from room where this furĆ
n ce, or ny other g s ppli nce (ie., w ter he tĆ
er), is inst lled. 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 pl ce when the
blower nd burners re oper ting. G s fumes, which
could cont in c rbon monoxide, c n be dr wn into
the living sp ce resulting in person l injury or de th.
Your furn ce is g s ppli nce. 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
C rbon monoxide g s is invisible, odorless nd
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 c rbon monoxĆ
ide detector in your home, even if you do not own g s
ppli nces. 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 strongly recommends nnu l inĆ
spection nd m inten nce of this ppli nce. Contact
your Lennox dealer for an inspection by a qualified service
technician.
Lighting Inform tion & Oper tion
WARNING
If you do not follow these instructions ex ctly, fire
or explosion m y result c using property d m ge,
person l injury or de th.
BEFORE LIGHTING 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.

Page 4
The gas valve on the G50UHi will be equipped with either
a gas control knob or lever. Use only your hand to turn the
gas control knob or push the gas lever. Never use tools. If
the knob or lever will not move by hand, do not try to repair
it. Call a qualified service technician. Force or attempted
repair may result in a fire or explosion.
Pl cing the G50UHi furn ce into oper tion:
G50UHi units are equipped with a SureLight® ignition sysĆ
tem. Do not attempt to manually light burners on these furĆ
naces. Each time 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 the SureLight® ignition sysĆ
tem.
Oper ting the G s V lve (Figures 3, 4 nd 5)
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 36E/36F Gas Valve - Switch gas
valve lever to OFF.
Honeywell VR8205 Gas Valve - Turn knob on gas
valve clockwise to OFF. Do not force. See figure
5.
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 36E/36F Gas Valve - Switch gas valve leĆ
ver to ON. See figure 3 for the White Rodgers 36E
valve and figure 4 for the White Rodgers 36F valve.
Honeywell VR8205 Gas Valve - Turn knob on gas valve
counterclockwise to ON. Do not force.
White Rodgers 36E Series G s V lve
GAS VALVE SHOWN IN OFF POSITION
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
MANIFOLD
PRESSURE
OUTLET
FIGURE 3
White Rodgers 36F Series G s V lve
GAS VALVE SHOWN IN OFF POSITION
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
MANIFOLD
PRESSURE
OUTLET
FIGURE 4
ON
OFF
Honeywell VR8205 Series G s V lve
GAS VALVE SHOWN IN OFF POSITION
MANIFOLD
PRESSURE
ADJUSTMENT
SCREW
MANIFOLD
PRESSURE
OUTLET
FIGURE 5
9 - Replace the upper access panel.
10 - Turn on all electrical power to to the unit.
11 - Set the thermostat to desired setting.
OTE - 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.
Turning Off G s 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.

Page 5
4 - White Rodgers 36E/36F Gas Valve - Switch gas
valve lever 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 G50UHi 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.
TABLE 1
Furn ce Filter Size
Furn ce
C binet 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)
M inten nce
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 ttempt to service
the unit in ny w y.
WARNING
ELECTRICAL SHOCK, FIRE,
OR EXPLOSION HAZARD.
F ilure to follow s fety w rnings ex ctly could result
in d ngerous oper tion, serious injury, de th or
property d m ge.
Improper servicing could result in d ngerous oper Ć
tion, serious injury, de th, or property d m ge.
Before servicing, disconnect ll electric l power to
furn ce.
When servicing controls, l bel ll wires prior to disĆ
connecting. T ke c re to reconnect wires correctly.
Verify proper oper tion fter servicing.
Venting System
WARNING
Asphyxi tion H z rd
The exh ust vent for this furn ce must be securely
connected to the furn ce flue coll r t ll times.
For your s fety nd to fulfill the terms of the limited
w rr nty, qu lified service technici n must nnu lĆ
ly inspect this furn ce nd 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 ccess p nel must be securely in pl ce
when the blower nd burners re oper ting. G s
fumes, which could cont in c rbon monoxide, c n
be dr wn into living sp ce resulting in person l injuĆ
ry or de th.
Burner Fl me
CAUTION
To ensure proper oper tion, qu lified technici n
should nnu lly check the burner fl me.
Electric l
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 __________________
S fety Prec utions
If you discover ny of the following, shut down your
unit, nd cont ct Lennox de ler for n inspection by
qu lified technici n.
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.
Pl nned 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 ir grilles nd 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 ppe r nce - Must be inspected for rust, dirt, signs
of water, burnt or damaged wires, or components.
Blower ccess door - Must be properly in place and proĆ
vide a seal between the return air and the room where the
furnace is installed.
Return ir duct - Must be properly attached and provide
an air seal to the unit.
Oper ting perform nce - Unit must be observed during
operation to monitor proper performance of the unit and the
vent system.
Combustion g ses - 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.
P y ttention to your furn ce. 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
Rep ir P rts List
The following repair parts are available through Lennox dealers. When ordering parts, include the complete furnace model
number listed on the CS nameplate -- Example: G50UHi-36 -070-1.
C binet P rts
Upper access panel
Blower access panel
Top Cap
Control P nel P rts
Transformer
SureLight® ignition board
Door interlock switch
Circuit Breaker
Blower P rts
Blower control module
Blower wheel
Motor
Motor mounting frame
Motor capacitor
Blower housing cutoff plate
He ting P rts
Flame Sensor
Heat exchanger assembly
Gas manifold
Combustion air inducer
Gas valve
Main burner cluster
Main burner orifices
Pressure switch
Ignitor
Primary limit control
Secondary limit
Flame rollout switch