Sequence Of Operation; Heating Cycle; Cooling Cycle - Trane 4YCY4042C Installer's Manual

Sequence of Operation

Operation of the unit heating and cooling cycles is automatic when
the system is set to HEAT or COOL (the optional automatic change-
over thermostat, when set to AUTO, automatically changes to heat
or cool with an appropriate room temperature change). The fan can
be set to ON, causing continuous evaporator (indoor) fan operation
or set to AUTO causing fan operation to coincide with heating or
cooling run cycles. Continuous fan mode during cooling operation
may not be appropriate in humid climates. If the indoor air exceeds
60% relative humidity or simply feels uncomfortably humid, it is
recommended that the fan only be used in the AUTO mode. 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 pres sure 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 energized
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 20
second prepurge. The gas valve (GV) is ener gized
stage to permit gas flow and the spark igniter (IP) is energized.
The flame detector (FD) confirms that igni tion 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 about 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
jumpers]), then will be de-energized by the control module.
Thermostat call for heat (1-stage Thermostat)
(R) and (W1/W2) (jumped) thermostat contacts close signaling 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) (jumped) contacts open signaling the control
module to close the gas valve and de-energize the induced
draft blower after approximately 5 second postpurge. The indoor
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 on the blower barrier,
and can be accessed through the blower compartment. This automatic
reset device protects against exces sive supply air temperature. If
this device opens, the gas valve is immediately closed and will not
permit operation until the limit switch closes.
The rollout switch (RO) is located in the gas compartment near the
inlet of the burners. This is a manual reset 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 (RO) must be reset 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 combus-
tion 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 igni-
tion period, the gas valve will be de-energized. The control (IGN)
will initiate a 60-second interpurge. Following the interpurge, the
control will perform a second ignition attempt. If the second try is
not successful, the control will start another 60-second interpurge.
After the interpurge, a third attempt will be tried. If the third try is
not successful, the control will lock out.
in the first 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 1 hour.
The control (IGN) can be reset by removing power to the unit or
by turning the thermo stat from ON to OFF for approximately three
seconds, then back ON.

Cooling Cycle

Thermostat call for cooling (2-stage thermostat)
Call for 1 stage cooling only:
st
With the room thermostat set to the COOL position and the fan
switch in the AUTO position, a call for cooling will supply power
to the unit from the room thermostat (Y1) and (G) terminal.
(Y1) provides power to the compressor contactor (CC). The
energized compressor contactor (CC) completes the circuit to the
compressor for 1
speed fan motor (ODM). (G) provides power to the (ECMC) for
low speed (IDM) indoor fan motor operation.
The thermostat will continue to cycle the compressor and fans to
maintain the desired temperature.
Call for 2 stage after 1st stage
nd
On a call for 2nd stage cooling, power is supplied from the room
thermostat (Y2) terminal to the compressor rectifier (ACR) and
the (ECMC). This energizes the (ACR) switching the compressor
to 2 nd stage (High) operation. With the compressor's internal
solenoid energized, both unloading orifices are closed enabling
the compressor to pump at full rated capacity. The (ECMC) is
energized for indoor fan motor (ECM) high speed fan operation.
The room thermostat will continue to cycle the system between
1 and 2 stage to maintain the desired temperature without any
st nd
cycling time delays in operation.
Installer's Guide
st stage (Low) operation and the outdoor single
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