Sequence Of Operation; Heating Cycle; Cooling Cycle - American Standard YCP-IOM-1C Installation Operation & Maintenance

The setting of the system switch on the room
thermostat controls the operation of the unit heat-
ing or cooling cycles. Once the system switch is
placed either in the "HEAT" or "COOL" position,
unit operation is automatic. A fan switch on the
thermostat also provides for continuous operation
of the evaporator fan when desired. The fan switch
"ON" position provides continuous operation while
the "AUTO" position provides operation during the
heating or cooling cycles.

HEATING CYCLE

On a call for heat by the room thermostat, the
control module (IGN) runs its self-check routine.
After the control has verified that the pressure
switch (PS) contacts are open, the limit switch
(TCO) contacts are closed, and the flame rollout
(FL) switch is closed, the combustion fan motor
(CFM) will be energized.
As the combustion fan motor (CFM) comes up to
speed, the pressure switch (PS) contacts will close.
After approximately 20 seconds, for the combus-
tion fan motor (CFM) prepurge, the gas valve (GV)
is energized permitting gas flow to the burners.
Concurrently, the spark ignitor (IP) is energized.
The flame detector (FD) confirms that ignition has
been achieved within the seven second trial period.
Upon proof of ignition, the delay to indoor fan on
period begins timing and after approximately 45
seconds, the indoor blower motor (IDM) will be
energized and will continue to run during the heat-
ing cycle.
When the thermostat is satisfied, the gas valve
(GV) will close and the flame will extinguish. The
combustion fan motor (CFM) will continue to run for
a postpurge period of approximately 5 seconds
then will be de-energized. The indoor blower motor
(IDM) will continue to run for the fan off period (field
selectable 60 or 90 seconds (by jumpers), then will
be de-energized by the control module.
SAFETY SEQUENCES AND LIMIT CONTROLS
During the main burner operation, if gas is inter-
rupted or discontinued, the gas valve (GV) is de-
energized instantly. The ignition control module
(IGN) then enters the retry mode. The retry mode
allows the control (IGN) to purge for 60 seconds.
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SEQUENCE OF OPERATION

Following this time period the valve is energized
and the spark is started. If the flame is not sensed
by the flame detector (FD) within 7 seconds the
valve is de-energized and the spark is stopped.
A second retry is then attempted. If this attempt at
ignition is unsuccessful, a third retry will be at-
tempted after a prepurge period. If this third at-
tempt at ignition is unsuccessful, the control will
lock out. It can be reset by removing power to the
unit or by turning the thermostat from "on" to "off" for
approximately three seconds, then back "on." If not
reset, the control module will automatically reset in
1 hour.
The temperature limit switch (TCO) protects against
overheating if the indoor motor (IDM) fails to oper-
ate. Also, a fusible link (FS) protects against flame
rollout due to flue blockage. These switches will
interrupt the operation of the unit by de-energizing
the ignition control module (IGM) if overheating
occurs.
The temperature limit switch (TCO) is located in the
gas compartment. This automatic reset device
protects against excessive leaving air tempera-
ture.
The fusible link (FS) is located in the gas compart-
ment near the burners. This is a single use device
designed to protect against any form of flame
rollout.

COOLING CYCLE

With the room thermostat system switch in the
"COOLING" position and the fan switch in the
"AUTO" position, the compressor contactor (CC)
and the indoor fan relay (F) are energized.
The energized compressor contactor (CC) com-
pletes the circuit to the compressor (CPR) and a
secondary circuit to the outdoor fan motor (ODM).
If the compressor safety controls are closed, the
compressor (CPR) will operate with the outdoor fan
motor (ODM). The indoor fan motor (IDM) will
operate. The thermostat will continue to cycle the
compressor and fans to maintain the desired tem-
perature.
With the thermostat fan switch in the "ON" posi-
tion, the indoor fan motor (IDM) will continue to
run regardless of compressor and condenser fan
operation.
Dwg. No. X664209 P01