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...

035-20465-001 Rev. A (0704)
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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...

035-20465-001 Rev. A (0704)
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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...

035-20465-001 Rev. A (0704)
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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...

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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...

035-20465-001 Rev. A (0704)
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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...

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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,...

035-20465-001 Rev. A (0704)
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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...

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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 

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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,...