Sequence Of Operation - American Standard YCY024G1L Installation Operation & Maintenance

Operation of the unit heating or cooling cycles is controlled by the
setting of the system switch on the room thermostat. 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 it 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
Thermostat call for heat (2-stage thermostat)
Call for 1st stage only:
(R) and (W1) thermostat contacts close signaling the control
module (IGN) to run 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 induced draft blower (CBM) will be ener-
gized on high speed for approximately 5 seconds.
After the induced draft blower (CBM) has come up to speed, the
control will verify that the pressure switch (PS) contacts are
closed and switch the induced draft blower to low speed for 10
second prepurge. The gas valve (GV) is energized in the first
stage to permit gas flow and the spark ignitor (IP) is energized.
The flame detector (FD) confirms that ignition has been achieved
within the 7 second trial period.
As the flame detector confirms that ignition has been achieved
the delay to indoor fan on period begins timing and after
approximately 45 seconds, the indoor blower motor (IDM) will be
energized at low speed and will continue to run during the
heating cycle.
Call for 2nd stage after 1st stage:
(R) and (W2) thermostat contacts close signaling a call for
second stage heat. The induced draft motor (CBM) is energized
on high speed and the gas valve on second stage. After
approximately 30 seconds the control energizes the indoor
blower on high speed.
2nd stage satisfied, 1st stage still called:
(R) and (W2) opens, the induced draft blower is reduced to low
speed the gas valve is reduced to first stage. After aprox. 30
seconds the indoor blower motor is reduced to low speed.
1st stage satisfied:
(R) and (W1) opens, the gas valve (GV) will close. The induced
draft blower (CBM) will be de-energized after approximately 5
seconds postpurge. The indoor blower motor (IDM) will continue
to run for the fan off period (field selectable 60 or 90 seconds [by
dip switch]), then will be de-energized by the control module.
Thermostat call for heat (1-stage Thermostat)
(R) and (W1/W2) (jumpered) thermostat contacts close signal-
ing a call for heat. 1st stage sequence of operation remains the
same as above. 2nd stage heat has a 10 minute delay from the
time of 1st stage ignition.
Thermostat satisfied:
(R) and (W1/W2) (jumpered) contacts open signaling the control
module to close the gas valve and de-energize the induced draft
blower after approximately 5 seconds postpurge. The I.D. blower
motor will continue to operate at the current speed for 60 or 90
seconds after the flames are extinguished .
SAFETY SEQUENCES
This product is equipped with safety devices to protect against
abnormal conditions.
The temperature limit switch (TCO) is located in the gas com-
partment on the vestibule panel above the burner assembly. This
automatic reset device protects against excessive leaving air
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SEQUENCE OF OPERATION

temperature. If this device opens, the gas valve is immediately
closed and will not permit operation until the limit switch closes.
The rollout switch (FS) is located in the gas compartment near
the inlet of the burners. This is a single use device designed to
protect against any form of flame rollout. If this device is opened
the gas valve is immediately de-energized and the control (IGN)
will lockout the system. The rollout switch (FS) must be replaced
before operation is allowed to continue.
The pressure switch (PS) is located in the upper right side of the
gas compartment. This automatic device assures adequate
combustion air pressure. If pressure against the induced draft
blower outlet becomes excessive, the pressure switch will react
and shut off the gas valve, until acceptable combustion pressure
is again available.
If the control (IGN) does not sense flame within the first trial for
ignition period, the gas valve will be de-energized. The control
(IGN) will initiate a 60 seconds interpurge. Following the
interpurge, on the second trial the gas valve will be energized on
second stage (high heat input). If the flame is sensed within 10
seconds after the second try and only a call for first stage exists,
the gas valve will be reduced to first stage. If the second try is
not successful, the control will start other 60 second interpurge.
After the interpurge, a third attempt will be tried. The gas valve
will be energized on second stage (high heat input). If the flame
is sensed within 10 seconds after the third try and only a call for
first stage exists, the gas valve will be reduced to first stage. If
the third try is not successful, the control will lock out.
If loss of flame occurs during a heating cycle, the control (IGN)
will close the gas valve and cycle through the ignition trial as
stated above.
If control lock out occurs, the control (IGN) will retry a complete
ignition sequence in 2 hours
The control (IGN) 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."
COOLING CYCLE
With the room thermostat system switch in the "COOLING"
position and the fan switch in the "AUTO" position, the com-
pressor contactor (CC) and the G-IGN are energized.
The energized compressor contactor (CC) completes 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 temperature.
With the thermostat fan switch in the "ON" position, the indoor fan
motor (IDM) will continue to run regardless of compressor and
condenser fan operation.
ICM FAN MOTOR ADJUSTMENTS
If the airflow needs to be increased or decreased, see the Indoor
Blower Performance Table in the Service Facts.. Information on
changing the dip switch settings for speed control of the blower
motor is in this table.
Blower speed changes are made on the ICM Fan Control
mounted in the control box. The ICM Fan Control controls the
variable speed motor.
There is a bank of 8 dip switches (See Figure 19), located at the
upper left side of the board. The dip switches work in pairs to
select the cooling/heat airflow (CFM/TON), and Fan off-delay
options.