York Model Gy8s User Instructions

							035-20465-001 Rev. A (0704)
USER’S INFORMATION,
MAINTENANCE AND 
SERVICE MANUAL
HIGH EFFICIENCY
TUBULAR HEAT EXCHANGER SERIES
MODELS: GY8S / GM8S / LY8S / LM8S / LF8
(Single Stage Upflow / Horizontal / LoNOx)
EFFICIENCY
RATING
CERTIFIED
This product was manufactured
in a plant whose quality system
is certified/registered as being
in conformity with ISO 9001.
The manufacturer recommends that the user read all sec-
tions of this manual and keep the manual for future refer-
ence.
 
SECTION I: USER’S INFORMATION
SAFETY
1. The furnace area must be kept clear and free of combustible mate-
rials, gasoline and other flammable vapors and liquids.
2. Insulating materials may be combustible. The furnace must be
kept free and clear of insulating materials. The furnace area must
be examined when installed in an attic or other insulated space or
when insulation is added to be sure that the insulation material has
been kept away from the furnace.
3. The furnace needs air for combustion in order to operate properly
and safely. Do not block or obstruct air openings on the furnace,
air openings to the area where the furnace is installed, or spaces
around the furnace.
4. Follow the instructions exactly as shown on the OPERATING
INSTRUCTION LABEL or the Start-up and Shutdown Instructions
on Page 3 of this manual when lighting the furnace or turning the
furnace off.
5. Should the gas supply fail to shut off or if overheating occurs, shut
off the gas valve to the furnace before shutting off the electrical
supply.
6. Do not use this furnace if any part has been under water. A flood-
damaged furnace is extremely dangerous. Attempts to use the fur-
nace can result in fire or explosion. A qualified service agency
should be contacted to inspect the furnace and replace all gas
controls, control system parts, electrical parts that have been wet
or the furnace if deemed necessary.
FIRE OR EXPLOSION HAZARD - Failure to follow safety
warnings exactly could result in serious injury, death, or prop-
erty damage.
— Do not store or use gasoline or other flammable
vapors and liquids in the vicinity of this or any other
appliance.
—  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 
(including cell phone) in your building.
• Leave the building immediately.
• 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 fire depart-
ment.
—  Installation and service must be performed by a quali-
fied installer, service agency or the gas supplier.
CONTACT INFORMATION
• Go to website at www.york.com click on “contact”, then click on “contact form” and follow the instructions.
• Contact us by mail:
York International
Consumer Relations
5005 York Drive
Norman, OK 73069
TABLE OF CONTENTSCONTACT INFORMATION   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
USER’S INFORMATION  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
SAFETY   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
INSTRUCTIONS FOR EXAMINING THE FURNACE 
INSTALLATION   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
HOW YOUR GAS FURNACE WORKS   . . . . . . . . . . . . . . . . . . . . . . 3
START-UP AND SHUTDOWN INSTRUCTIONS  . . . . . . . . . . . . . . . 3
Read the Instructions Below Before Trying to Start the Furnace . . 3
Operating Instructions: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
To Turn Off the Appliance: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
FURNACE USER MAINTENANCE   . . . . . . . . . . . . . . . . . . . . . . . . . 4
Air Filters  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Removing Filters   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Blower Care  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Motor Lubrication  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
SERVICE AND MAINTENANCE MANUAL   . . . . . . . . . . . . . . . . . . . . 5
SAFETY SECTION  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5FURNACE MAINTENANCE SECTION  . . . . . . . . . . . . . . . . . . . . . . .5
FURNACE CLEANING SECTION  . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Burner Removal/Cleaning   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Cleaning the Heat Exchanger   . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
SEQUENCE OF OPERATION   . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Continuous Blower  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Intermittent Blower - Cooling   . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Heating Cycle  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Hot Surface Ignition System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
TROUBLESHOOTING   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
FURNACE CONTROL DIAGNOSTICS  . . . . . . . . . . . . . . . . . . . . . . .6
DIAGNOSTIC FAULT CODE STORAGE AND RETRIEVAL   . . . . . .7
REPLACEMENT PARTS LIST   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
FIELD INSTALLED ACCESSORIES - NON-ELECTRICAL   . . . . . . .8
REPLACEMENT PART CONTACT INFORMATION . . . . . . . . . . . . .10
WIRING DIAGRAM   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
LIMITED WARRANTY  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12 
						

							035-20465-001 Rev. A (0704)
2Unitary Products Group
7. NEVER . . .Store flammable materials of any kind near your fur-
nace. Gasoline, solvents, and other volatile liquids should be
stored only in approved containers outside your home. These
materials vaporize easily and are extremely dangerous.
8. NEVER . . .Store cleaning materials near your furnace. Materials
such as bleaches, detergents, powdered cleansers, etc., can
cause corrosion of the heat exchangers. 
9. NEVER . . . Use the area around your furnace as a storage area
for items which could block the normal flow of air. This flow of air is
required for ventilation of the various furnace components.
INSTRUCTIONS FOR EXAMINING THE FURNACE 
INSTALLATION
It is the owner’s responsibility to ensure that an annual inspection of the
entire heating portion of the unit is made by a qualified service agency.
Examine the furnace as outlined below in steps “1 - 6” before each
heating season. Use Figure 3 for visual reference.
1. Examine the heat exchanger, vent pipe, combustion air passes
gas, vent connectors and chimney to be sure they are clear and
free of obstructions.
2. Examine the vent pipe making sure it is firmly in place, that it
slopes slightly upward and is physically sound without holes and
all of the connections are secure.
3. Examine the return-air duct connections to make sure they are
physically sound, sealed to the furnace casing, and the ducts ter-
minate outside the space containing the furnace.
4. Examine the furnace casing making sure the physical support is
sound without sagging, cracks or gaps. Examine the furnace base
making sure it is physically sound without cracks, gaps or sagging
and has a good seal.
5. Examine the furnace casing for obvious signs of deterioration.
6. Examine the burner flames to make sure they are in good adjust-
ment. Refer to the pictorial sketch shown in Figure 2 as a compari-
son to the actual flame.  FIGURE 1: Component Locations
FIRE OR EXPLOSION HAZARD
This furnace is designed and approved for use with Nat-
ural Gas and (LP) Propane Gas ONLY. DO NOT BURN
ANY LIQUID FUEL OR SOLID FUEL IN THIS FURNACE.
Burning any unapproved fuel will result in damage to the
furnace heat exchanger, which could result in Fire, Per-
sonal Injury, and/or Property Damage.
VENT PIPE
PRESUURE
SWITCH
SILICONE
TUBE
INDUCER
SHIELD
GAS VALVE
FLAME
SENSORINDUCED DRAFT
ASSEMBLY
INDUCED DRAFT
MOTOR
LIMIT
SWITCH
IGNITOR
MANIFOLD
PIPE
SAFETY SHUTOFF
SWITCH
CONTROL
BOARD FLUE
COLLAR
ELECTRICAL
JUNCTION BOX
 FIGURE 2: Burner Flame Drawing
BLUE CONE PORTION OF FLAME SHOULD
ENTER HEAT EXCHANGER TUBE
 FIGURE 3: Furnace Examination Checkpoints
4
EXAMINE
FURNACE
CASING6
5
343 1
6
EXAMINE
RETURN AIR
DUCT
CONNECTIONREMOVE
PANEL
TO EXAMINE
BURNER
FLAMES EXTERNAL HEAT EXCHANGER INTERNAL
VENT COMBUSTION AIR PIPE. MUST
REMOVE PANEL TO EXAMINE.
EXAMINE ENTIRE
FURNACE CASING
SHOWN IN ALL
DRAWINGS
EXAMINE
RETURN AIR
DUCT
CONNECTION
(side or bottom) REMOVE
PANEL
TO EXAMINE
BURNER
FLAMESEXAMINE EXTERNAL
VENT PIPE
EXAMINE
FURNACE
CASING 
						

							035-20465-001 Rev. A (0704)
Unitary Products Group3
HOW YOUR GAS FURNACE WORKS
Your furnace is a very easy appliance to take for granted. Season after
season, it sits there in your home, keeping you warm and comfortable.
For this reason, you may never have given much thought to the way
your furnace operates. In order to get the safest and most efficient oper-
ation from your furnace, you should understand how your furnace does
its job.
When you set your thermostat to provide more heat in your home, you
are starting the heating cycle of the furnace. First, the inducer motor
starts to purge the heat exchanger of any remaining gases. Next, the
hot surface ignitor glows and after a warm-up period the gas valve
opens and ignition occurs. A short time later, the blower starts and dis-
tributes the warm air throughout the home. When the temperature set-
ting on your thermostat is reached, the gas valve closes, the main
burners are turned off, and the blower continues to run until the remain-
ing warm air in the system is distributed. When the blower stops, the
heating cycle has ended.
START-UP AND SHUTDOWN INSTRUCTIONS
Read the Instructions Below Before Trying to Start the 
Furnace
A. This appliance does not have a pilot. It is equipped with an ignition
device which automatically lights the burner. Do not try to light the
burner by hand.
B. BEFORE OPERATING; 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.
C. Use only your hand to push the gas control switch to the “on” posi-
tion. Never use tools. If the switch will not operate by hand, don’t
try to repair it, call a qualified service technician. Force or
attempted repair may result in a fire or explosion.
D. Do not use this appliance if any part has been under water. Imme-
diately call a qualified service technician to inspect the appliance
and to replace any part of the control system and any gas control,
which has been under water.
Operating Instructions:
1. STOP! Read the safety information above.
2. Set the thermostat to the lowest setting.
3. Turn off all electric power to the appliance.
4. Remove furnace door.
5. Move gas control switch to the “OFF” position. Do not force. See
Figure 4.
6. Wait five (5) minutes to clear out any gas. If you then smell gas,
STOP! Follow “B” in the safety information above. If you don’t
smell gas, go to next step.
7. Move gas control switch to the “ON” position. Do not force. See
Figure 4.
8. Replace burner access panel.
9. Turn on all electric power to the appliance.
10. Set thermostat to the desired setting. Burner will light, which may
take 30-60 seconds.
11. After three (3) trials for ignition, if the appliance will not operate fol-
low the instructions, “TO TURN OFF THE APPLIANCE” and call
your service technician or gas supplier.
To Turn Off the Appliance:
1. Set the thermostat to lowest setting.
2. Turn off all electric power to the appliance if service is to be per-
formed.
3. Remove burner access panel.
4. Move gas control switch to the “OFF” position. See Figure 4.
5. Replace burner access panel.
NOTE: The spring-loaded safety cut-off switch, mounted under the
blower deck will automatically cut off the electrical power supply
to the furnace when the blower panel is removed. As a safety
precaution, all electrical power and the gas supply to the furnace
should be turned off before servicing.
If you do not follow these instructions exactly, a fire or
explosion may result causing property damage, personal
injury, and/or loss of life.
Should overheating occur, or the gas valve fail to shut off,
turn the external manual gas valve in the gas supply line to
the furnace to the “off” position and let the furnace cool off
before shutting off the electrical power supply. Refer to
Figure 5.
 FIGURE 4: Gas Valve
 FIGURE 5: Upflow Gas Piping
 FIGURE 6:  Horizontal Gas Piping
INLET
WRENCH
BOSS
INLET
PRESSURE
PORT
ON
OFF
ON/OFF SWITCH
(Shown in ON position)MAIN REGULATOR
ADJUSTMENTOUTLET OUTLET
PRESSURE
PORT
VENT PORT
EXTERNAL MANUAL
SHUTOFF VALVE
TO GAS
SUPPLY TO GAS
SUPPLY
GROUNDED JOINT UNION
MAY BE INSTALLED
INSIDE OR OUTSIDE UNIT. DRIP
LEG
MANUAL
SHUT-OFF
VA LV E
DRIP
LEG
GAS
PIPE
GAS BURNERS
GAS VALVE
GAS
PIPE
DRIP
LEGMANUAL
SHUT-OFF VALVE 
						

							035-20465-001 Rev. A (0704)
4Unitary Products Group
FURNACE USER MAINTENANCE
Every time the filters are changed the following items should be visually
inspected:
• Check combustion air and vent pipe for blockage or leakage.
• Check all components to be sure they are in good condition and
that there are no obvious signs of deterioration.
• Check the drain lines to make sure there are no cracks or leaks.
• Check for dirt or lint on any surfaces or on components. Do not try
to clean any of the surfaces or components. Cleaning of the fur-
nace and its components must be done by a qualified service pro-
fessional.
If, during the inspection of your furnace, you find any of the following
conditions:
• Excessive amounts of dust and lint on components.
• Damaged or deteriorated components or surfaces.
• Leaks or blockage in the vent pipe passages.
• Water on any surface inside or outside of the furnace.
Do not operate the furnace, call a certified dealer / servicing contractor
to check and / or clean your furnace, or for more information if you have
questions about the operation of your furnace.
If all components appear to be in good operating condition, replace the
front panels. Turn ON the gas and electrical power supplies to the fur-
nace, and set thermostat to the desired temperature.
Air Filters
Dirty filters greatly restrict the flow of air and may cause damage to the
moving parts of the furnace. If the filters become clogged the heat
exchangers and blower motor could overheat resulting in a potentially
dangerous situation. The filters should be checked every 3 months. On
new construction, check the filters every week for the first four weeks
and every three weeks after that, especially if the indoor fan is running
continuously. When replacing the filter(s) you must use filters that are
the same size as those recommended in Table 1. Never operate your
furnace without a suitable air filter.
Removing Filters
Externally Mounted Air Filters
The air filter should be located in a rack attached to the casing of the
furnace or placed in the return air duct. You can gain access to the filter
by pulling on the door or unscrewing the retaining screw, then slide the
filter(s) out of its channel. Replace throw away filter(s) with the same
size new filter(s). Throw away filter(s) may be replaced with cleanable
filter(s) at this time. Cleanable filter(s) may be cleaned as described in
the manufacturer instructions or as described below and then re-
installed.
To replace the filter after cleaning you must do the following:
1. Slide filter into place.
2. Snap the door on or place the door in position and tighten the
retaining screws, if provided.
3. Make sure the door is secure to the end of the filter rack.How to Clean your Filter
High-velocity filters may be cleaned with a vacuum cleaner or washed
with a garden hose. Be sure to shake off excess water and allow filter to
completely dry before re-installing the filter.
Blower Care
Even with good filters properly in place, blower wheels and motors will
become dust laden after long months of operation. The entire blower
assembly should be inspected annually. If the motor and wheel are
heavily coated with dust, they can be brushed and cleaned with a vac-
uum cleaner. If the blower cannot be properly cleaned without removing
it from the furnace, then this service must be performed by a qualified
service agency.
Motor Lubrication
The motors in these furnaces are permanently lubricated, and do not
require periodic oiling.
Every time the filters are changed the following items should be visually
inspected:
• Check combustion air and vent pipe for blockage or leakage.
• Check all components to be sure they are in good condition and
that there are no obvious signs of deterioration.
• Check the drain lines to make sure there are no cracks or leaks.
• Check for dirt or lint on any surfaces or on components. Do not try
to clean any of the surfaces or components. Cleaning of the fur-
nace and its components must be done by a qualified service pro-
fessional.
If, during the inspection of your furnace, you find any of the following
conditions:
• Excessive amounts of dust and lint on components.
• Damaged or deteriorated components or surfaces.
• Leaks or blockage in the vent pipe passages.
• Water on any surface inside or outside of the furnace.
Do not operate the furnace, call a certified dealer / servicing contractor
to check and / or clean your furnace, or for more information if you have
questions about the operation of your furnace.
If all components appear to be in good operating condition, replace the
front panels. Turn ON the gas and electrical power supplies to the fur-
nace, and set thermostat to the desired temperature.
Before proceeding, be sure the area is well ventilated. Turn
the thermostat OFF. If the blower is running, wait until it
stops automatically. Turn OFF the gas and electrical power
supplies to the furnace. Check all metal parts and surfaces
to be sure they have cooled to room temperature before
you begin.
TA B L E  1 :  Filter Sizes
Cabinet Size Side (in) Side (mm) Bottom (in) Bottom (mm)
A 16 x 25 40.6 x 63.5 14 x 25 35.6 x 63.5
A 16 x 25 40.6 x 63.5 14 x 25 35.6 x 63.5
A 16 x 25 40.6 x 63.5 14 x 25 35.6 x 63.5
B 16 x 25 40.6 x 63.5 16 x 25 40.6 x 63.5
C (2) 16 x 25 (2) 40.6 x 63.5 20 x 25 50.8 x 63.5
B 16 x 25 40.6 x 63.5 16 x 25 40.6 x 63.5
B 16 x 25 40.6 x 63.5 16 x 25 40.6 x 63.5
C (2) 16 x 25 (2) 40.6 x 63.5 20 x 25 50.8 x 63.5
C 16 x 25 40.6 x 63.5 20 x 25 50.8 x 63.5
C (2) 16 x 25 (2) 40.6 x 63.5 20 x 25 50.8 x 63.5
D (2) 16 x 25 (2) 40.6 x 63.5 22 x 25 55.9 x 63.5
Make sure you DO NOT move the clip on weight on the
indoor fan wheel when cleaning the wheel. This weight is
used to balance the wheel. Moving the weight will cause
the fan wheel to vibrate. 
						

							035-20465-001 Rev. A (0704)
Unitary Products Group5
SECTION II: SERVICE AND MAINTENANCE 
MANUAL
SAFETY SECTION
The following safety rules must be followed when servicing the
furnace.
FURNACE MAINTENANCE SECTION
The furnace should be cleaned and adjusted by a certified dealer or
qualified service contractor once a year or before the start of every
heating season. The following items must be cleaned and serviced or
replaced if there are signs of deterioration.
1. The vent terminal.
2. The furnace vent and combustion air intake passageways. Should
it be necessary to service the vent/air intake system, the manufac-
turer recommends this service be conducted by a qualified service
agency. The operation of this appliance requires the reassembly
and resealing of the vent/air intake system.
3. The furnace burners, ignitor and flame sensor.
4. The condensate collection and disposal system. If any disassem-
bly of components containing flue or vent gases is required, a
qualified service agency must perform the service.
FURNACE CLEANING SECTION
NOTE: The cleaning operations listed below must be performed only by
a qualified service agency.
Burner Removal/Cleaning
The main burners should be checked periodically for dirt accumulation.
If cleaning is required, follow this procedure:
1. Turn off the electrical power to the unit.
2. Turn off the gas supply at the external manual shut-off valve and
loosen the ground union joint.
3. Remove the upper access panel and remove the burner box
cover.
4. Disconnect wires from flame sensor, rollout switch and HSI igniter.
Remove igniter carefully, as it is easily broken.
5. Remove the screws that hold the burner box assembly to the vest
panel and remove the assembly.
6. Remove burners from the burner assembly.
7. Burners may be cleaned by rinsing in hot water.
8. Reassemble the burners in the reverse order.
Cleaning the Heat Exchanger
Lower Heat Exchanger Access
1. Turn off the electrical power to the unit and turn off gas supply at
the shutoff valve.
2. Remove the blower and burner compartment access doors. Dis-
connect the gas supply piping at the union to permit removal of the
entire burner and gas control assembly from the vestibule panel.Use the wrench boss on the gas valve when removing or installing
this piping. See Figure 4.
3. Unplug the igniter from the wire harness. Disconnect sensor and
rollout switch wires located on top of the air shield. Identify and
note the location of all leads for ease of reinstallation. Also discon-
nect the wires at the side rollout switches (upflow only) and the
gas valve wires.
4. Remove the screws holding the burner assembly to the vestibule
panel and remove this assembly. Handle the assembly carefully
since it contains the igniter, which is fragile and easily broken. The
lower portion of the heat exchanger will now be exposed. To clean
the burner assembly, use a vacuum cleaner, or remove the burn-
ers as outlined in burner cleaning, and clean in hot water.
Upper Heat Exchanger Access
1. Perform steps 1-4 above.
2. Disconnect vent piping from the vent motor assembly at the top
panel on the furnace (upflow only). On downflow models, the vent
pipe is secured to the vent motor outlet with a screw. Remove this
screw before proceeding.
3. Unplug the vent motor wires and ground wire. Remove the pres-
sure switch tubing at the top on the vent motor housing.
NOTE: It is recommended that replacement gaskets be available
before removing vent motor.
1. Remove six mounting screws that hold the vent motor to the
restrictor plate. The surface is gasketed and the gasket can be
reused if it is carefully removed. It is necessary to remove this
assembly to gain access to the restrictor plate mounting holes.
The assembly may be vacuumed if cleaning is necessary. If any
vent assembly parts are damaged, replace with an entire new
assembly (except for gaskets).
2. Remove the perimeter screws attaching the restrictor plate assem-
bly to the vestibule panel. The surface is also gasketed. The
assembly, including the flue baffle plate (rear) may be vacuumed
or cleaned with hot water if necessary.
3. The upper portion of the heat exchanger is now accessible. With a
long flexible wire brush, clean inside each tube at both the top and
bottom. The brush must pass around the rear heat exchanger
tubes. Vacuum loose scale and dirt from each tube.
4. Clean - Replace all components in reverse order. Re-gasket all
surfaces which required a gasket. Reconnect all wiring. Reattach
vent pipe and gas supply lines before restoring service to furnace.
Restore electrical power, check gas supply piping for leaks, and
then verify furnace operation.
SEQUENCE OF OPERATION
The following describes the sequence of operation of the furnace. Refer
to Figure 1 for component location.
Continuous Blower
Cooling/heating thermostats have a fan switch that has an ON and
AUTO position. In the ON position the thermostat circuit is completed
between terminals R and G. The motor will operate on the speed tap
wire that is connected to the “HI COOL” cooling terminal on the control
board. To obtain a constant air circulation at lower flow rate, change the
high-speed wire to either the medium speed wire or the low speed wire.
ELECTRIC 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, and death or property damage.
• Before servicing, disconnect all electrical power to the fur-
nace. 
• When servicing controls, label all wires prior to disconnect-
ing. Reconnect wires correctly. 
• Verify proper operation after servicing.
Label all wires prior to disconnection when servicing
controls. Wiring errors can cause improper and danger-
ous operation. Verify proper operation after servicing. 
						

							035-20465-001 Rev. A (0704)
6Unitary Products Group
Intermittent Blower - Cooling
Cooling/heating thermostats have a fan switch that has an ON and
AUTO position. In the AUTO position the thermostat circuit is completed
between terminals R and G when there is a call for cooling. The motor
will operate on the speed tap wire that is connected to the “HI COOL”
cooling terminal on the control board. The fan off setting is fixed at 60
seconds to improve cooling efficiency.
Heating Cycle
When the thermostat switch is set on HEAT and the fan is set on AUTO,
and there is a call for heat, a circuit is completed between terminals R
and W of the thermostat. When the proper amount of combustion air is
being provided, the pressure switch will close, the ignition control pro-
vides a 17-second warm-up period, the gas valve then opens, the gas
starts to flow, ignition occurs and the flame sensor begins its sensing
function. The blower motor will energize 30 seconds after the gas valve
opens, if a flame is detected. Normal furnace operation will continue
until the thermostat circuit between R and W is opened, which causes
the ignition system and gas valve to de-energize and the burner flames
to be extinguished. The vent motor will operate for 15 seconds and the
blower motor will operate for the amount of time set by the fan-off delay
jumper located on the control board. See Figure 10. The heating cycle
is complete, and ready for the start of the next heating cycle.
If the flame is not detected within 7 seconds of the gas valve opening,
the gas valve is shut off and a retry operation begins. If the flame is lost
for 2 seconds during the 10-second stabilization period, the gas valve is
shut off and a retry operation begins. During a retry operation, the vent
motor starts a 15 second inter-purge and the ignitor warm-up time is
extended to 27 seconds. If the flame is established for more than 10
seconds after ignition during a retry, the control will clear the ignition
attempt (retry) counter. If three retries occur during a call for heat, the
furnace will shut down for one hour. If at the end of the one hour shut
down there is a call for heat, the furnace will initiate a normal start cycle.
If the problem has not been corrected the furnace will again lockout
after three retries.
A momentary loss of gas supply, flame blowout, or a faulty flame probe
circuit will result in a disruption in the flame and be sensed within 1.0
seconds. The gas valve will de-energize and the control will begin a
recycle operation. A normal ignition sequence will begin after a 15 sec-
ond inter-purge. If during the five recycles the gas supply does not
return, or the fault condition is not corrected the ignition control will lock-
out for 60 minutes.During burner operation, a momentary loss of power for 50 milliseconds
or longer will de-energize the gas valve. When the power is restored,
the gas valve will remain de-energized and the ignition sequence will
immediately restart.
Hot Surface Ignition System
TROUBLESHOOTING
The following visual checks should be made before troubleshooting:
1. Check to see that the power to the furnace and the ignition control
module is ON.
2. The manual shut-off valves in the gas line to the furnace must be
open.
3. Make sure all wiring connections are secure.
4. Review the sequence of operation. Start the system by setting the
thermostat above the room temperature. Observe the system’s
response. Then use the troubleshooting section in this manual to
check the system’s operation.
FURNACE CONTROL DIAGNOSTICS
The furnace has built-in, self-diagnostic capability. If a system problem
occurs, a blinking LED shows a fault code. The LED can flash red,
green or amber to indicate various conditions. It is located behind a
clear view port in the blower compartment door.
The control continuously monitors its own operation and the operation
of the system. If a failure occurs, the LED will indicate the failure code. If
the failure is internal to the control, the light will stay on continuously. In
this case, the entire control should be replaced, as the control is not
field repairable.
Flash sequence codes 1 through 10 are as follows: LED will turn “on”
for 1/4 second and “off” for 1/4 second. This pattern will be repeated the
number of times equal to the code. For example, six “on” flashes equals
a number 6 fault code. All flash code sequences are broken by a 2 sec-
ond “off” period.
SLOW GREEN FLASH: Normal operation.
SLOW AMBER FLASH: Normal operation with call for heat.
RAPID RED FLASH: Twinning error, incorrect 24V phasing. Check
twinning wiring.
RAPID AMBER FLASH: Flame sense current is below 1.5 microamps.
Check and clean flame sensor. Check for proper gas flow.
1 RED FLASH: This indicates that flame was sensed when there was
not a call for heat. With this fault code the control will turn on both the
inducer motor and supply air blower. A gas valve that leaks through or
is slow closing would typically cause this fault.  FIGURE 7: Typical Heat/Cool Speed Tap Connections
PARK
PARK
HI COOL
HEAT
EAC
L1
XFMR
HUMNEUTRALS
YELLOW - MED. LOW SPEED
BLACK - HIGH SPEED
BLUE -MED. HIGH SPEED
FAN OFF
ADJUSTMENT
JUMPER
Y/Y2
WRG
C
HOT SURFACE IGNITION SYSTEM
Do not attempt to light this furnace by hand (with a
match or any other means). There may be a potential
shock hazard from the components of the hot surface
ignition system. The furnace can only be lit automatically
by its hot surface ignition system.
Never bypass any safety control to allow furnace opera-
tion. To do so will allow furnace to operate under poten-
tially hazardous conditions.
Do not try to repair controls. Replace defective controls
with UPG Source 1 Parts.
Never adjust pressure switch to allow furnace operation. 
						

							035-20465-001 Rev. A (0704)
Unitary Products Group7
2 RED FLASHES: This indicates that the normally open pressure
switch contacts are stuck in the closed position. The control confirms
these contacts are open at the beginning of each heat cycle. This would
indicate a faulty pressure switch or miswiring.
3 RED FLASHES: This indicates the normally open pressure switch
contact did not close after the inducer was energized. This could be
caused by a number of problems: faulty inducer, blocked vent pipe, bro-
ken pressure switch hose or faulty pressure switch.
4 RED FLASHES: This indicates that a primary or auxiliary limit switch
has opened its normally closed contacts. With this fault code the control
will operate the supply air blower and inducer. This condition may be
caused by: dirty filter, improperly sized duct system, incorrect blower
speed setting, incorrect firing rate or faulty blower motor.
5 RED FLASHES: This fault is indicated if the normally closed contacts
in the rollout switch opens. The rollout control is manually reset. If it has
opened, check for proper combustion air, proper inducer operation, and
primary heat exchanger failure or burner problem. Be sure to reset the
switch after correcting the failure condition.
6 RED FLASHES: This indicates that after the unit was operating, the
pressure switch opened 4 times during the call for heat. If the main
blower is in a “Delay on” mode it will complete it, and any subsequent
delay off period. The furnace will lock out for one hour and then restart.
7 RED FLASHES: This fault code indicates that the flame could not be
established. This no-light condition occurred 3 times (2 retries) during
the call for heat before locking out. Low gas pressure, faulty gas valve,
faulty hot surface ignitor or burner problem may cause this. The furnace
will lock out for one hour and then restart.
8 RED FLASHES: This fault is indicated if the flame is lost 5 times (4
recycles) during the heating cycle. This could be caused by low gas
pressure or faulty gas valve. The furnace will lock out for one hour and
then restart.
9 RED FLASHES: Indicates reversed line voltage polarity or grounding
problem. Both heating and cooling operations will be affected. Check
polarity at furnace and branch. Check furnace grounding. Check that
flame probe is not shorted to chassis.
10 RED FLASHES: Gas valve energized with no call for heat. Check
gas valve and gas valve wiring.
11 RED FLASHES: This indicates that a primary or auxiliary limit switch
has opened its normally-closed contacts and has remained open for
more than five minutes. This condition is usually caused by a failed
blower motor or blower wheel.
STEADY ON RED: Control failure. Replace control board.60-MINUTE AUTOMATIC RESET FROM LOCKOUT: This control
includes a “watchdog” type circuit that will reset from a lockout condition
after 60 minutes. Operational faults 6,7,8 will be reset. This provides
protection to an unoccupied structure if a temporary condition exists
causing a furnace malfunction. An example would be a low incoming
gas supply pressure preventing unit operation. When the gas pressure
is restored, at some point the “watchdog” would restart the unit and pro-
vide heat for the house.
NOTE: If a flame is detected the control flashes the LED for 1/8 of a
second and then enters a flame stabilization period.
DIAGNOSTIC FAULT CODE STORAGE AND 
RETRIEVAL
The control in this furnace is equipped with memory that will store up to
five error codes to allow a service technician to diagnose problems
more easily. This memory will be retained even is power to the furnace
is lost. This feature should only be used by a qualified service tech-
nician. 
The control stores up to five separate error codes. If more than five
error codes have occurred since the last reset, only the five most recent
will be retained. The furnace control board has a button, labeled LAST
ERROR that is used to retrieve error codes. This function will only work
if there are no active thermostat signals. So any call for heating, cooling
or continuous fan must be terminated before attempting to retrieve error
codes. 
To retrieve the error codes, push the LAST ERROR button. The LED on
the control will then flash the error codes that are in memory, starting
with the most recent. There will be a two-second pause between each
flash code. After the error codes have all been displayed, the LED will
resume the normal slow green flash after a five second pause. To
repeat the series of error codes, push the button again.
If there are no error codes in memory, the LED will flash two green
flashes. To clear the memory, push the LAST ERROR button and hold it
for more than five seconds. The LED will flash three green flashes when
the memory has been cleared, then will resume the normal slow green
flash after a five-second pause.IGNITION CONTROL (P/N 031-01973-000)
Normal flame sense current is approximately
3.7 microamps DC (µa)
Low flame signal warning starts at 1.5 microamps.
Low flame signal control lockout point is
0.9 microamps DC (µa) 
						

							035-20465-001 Rev. A (0704)
8Unitary Products Group
SECTION III: REPLACEMENT PARTS LIST
FIELD INSTALLED ACCESSORIES - NON-ELECTRICAL
 FIGURE 8: Furnace Control Event Schedule
Thermostat Calling for HeatThermostat Satisfied
(Seconds)
THERMOSTAT
INDUCER
IGNITOR
MAIN VALVE
HUMIDIFIER
ELECTRONIC
AIR CLEANER
CIRCULATING
BLOWEROFF
OFF
OFF
OFF
OFF
OFF
OFF
ON
ON
ON
ONOFF
OFF
OFF
OFFON
ON
ON
OFF
OFF
OFFOFF
OFF
OFF
OFF 15 Sec.
Post
Purge Fan on Delay
30 Seconds 0
2
17 2252
0
60, 90, 120, 180 SEC.
Selectable Fan Off Delay
TABLE 2: Field Installed Accessories - Non-electrical
MODEL NO. DESCRIPTION USED WITH
1NP0347
PROPANE (LP) CONVERSION KIT040, 080,100
1NP0348060, 115, 130
1PS0301
HIGH ALTITUDE PRESSURE SWITCH KIT 
(Does Not Include Orifices)SEE CHART BELOW 1PS0302
1PS0311
1PS0312
1BR0314
EXTERNAL BOTTOM RETURN FILTER, with High Velocity Filter for Horizontal 
Application for Upflow Bottom Return Application.14-1/2” CABINETS
1BR031717-1/2” CABINETS
1BR032121” CABINETS
1BR032424-1/2” CABINETS
1CB0314
COMBUSTIBLE FLOOR BASE for Downflow Units14-1/2” CABINETS
1CB031717-1/2” CABINETS
1CB032121” CABINETS
1CB032424-1/2” CABINETS
1SR0302 EXTERNAL SIDE FILTER RACK - with Filter Rack (6 pack) ALL MODELS
HIGH PRESSURE SWITCH 
Input (MBH) Output (MBH)2,000 Ft. to 5,500 
Ft.>5,500 Ft. to10,000 
Ft.
40 32 1PS0301 1PS0301
60 48 1PS0301 1PS0301
80 64 1PS0302 1PS0302
100 80 1PS0312 1PS0311
115 92 1PS0312 1PS0311
130 104 1PS0312 1PS0311 
						

							035-20465-001 Rev. A (0704)
Unitary Products Group9
27
3
30
265 10 92224112 29
8
23
12
7
17
19
21
13
1
16
154
4340
28
25
39
37 6,20
31
12A
7
3524
3612
19
11 
						

							035-20465-001 Rev. A (0704)
10Unitary Products Group
ITEM DESCRIPTION
MOTOR
1MOTOR,DIRECT DRIVE BLOWER
2 MOTOR,VENTOR ASS’Y
ELECTRICAL
3 CAPACITOR
4 CONTROL, HIGH LIMIT
5 CONTROL, FURACE
6IGNITER
7 SENSOR, FLAME
8 SWITCH, AIR PRESSURE   [1LP]
9 SWITCH, DOOR                     [SW]
10 TRANSFORMER
11 VALVE, GAS
12 CONTROL, LIMIT (Top)
12ACONTROL, LIMIT (Side, 2 Req’d)
13CONTROL, AUX LIMIT (2 Req’d)
14* FUSE
AIR MOVING
15 HOUSING, BLOWER
16 WHEEL, BLOWER
16A PANEL, FILLER WRAP
FABRICATED PARTS
17 SHIELD, SECONDARY AIR
18* BAFFLE, FLUE
19 BURNER, MAIN GAS
20 BRACKET, IGNITER
21 DECK, BLOWER (Rear)
22 DECK, FRONT
23 HEAT EXCHANGER ASS’Y
 (Primary) 
24 MANIFOLD, GAS
25 PANEL, VEST ACCESS (Burner)
26 PAN, BASE
27 PANEL, BLOWER ACCESS 
28 PANEL, TOP
29 WRAPPER, INSULATED
30 CHANNEL, TOE PLATE
31 BASE FRAME, SIDE (2 Req’d)
32* PLATE, RESTRICTOR
33* SHIELD, INDUCER 
34 BRACKET, ROLL-OUT SWITCH
MISCELLANEOUS
35* FILTER
36* RACK, FILTER
37 PLUG HOLE WINDOW CLEAR-.875”
38 ORIFICE, BURNER
 (Natural #45)
39 HANDLE, DOOR
40 COLLAR, FLUE
41* GROMMET, 1/2” DIA.
42* GASKET, RESTRICTOR PLATE
43 TUBING, SILICONE
44* SPRING, DOOR
45* WIRING DIAGRAM
46* WIRING HARNESS
47* ISOLATOR, TUBE (3 Req’d)
48* ISOLATOR, WASHER (3 Req’d
)
49* ISOLATOR, SLEEVE (3 Req’d)
50* MOTOR MOUNT
51* BEZEL/LOGO PLATE ASSY
52* LO-NOX SCREEN (L-Models only) ITEM DESCRIPTION
NOTE: *Not Shown
Major components and suggested stocking items are shown with shaded item number.
REPLACEMENT PART CONTACT INFORMATION
This is a generic parts list. To request a complete parts list, refer to the contact information below:
• Visit our website at www.source1parts.com for the following information:
1. Search for a part or browse the catalog.
2. Find a dealer or distributor.
3. Customer Service contact information.
a. Click on the “Brand Links” button
b. Click on the “Customer Service” button
• You can contact us by mail. Just send a written request to:
York International
Consumer Relations
5005 York Drive
Norman, OK 73069