Sequence Of Operation - Trane 4YCY4024 Installer's Manual

Installer's Guide

Sequence of Operation

Operation of the unit heating or cooling cycles is controlled by the
setting of the comfort control. Once the comfort control is set to
either HEAT or COOL, unit operation is automatic. A fan setting
on the comfort control also provides for continuous operation of
the indoor fan when desired. The fan, when set to ON provides
continuous operation, while AUTO provides operation during
the heating or cooling 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.
Heating Cycle
Comfort Control 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.
Comfort Control call for heat (1-stage Comfort Control)
(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.
Comfort Control 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 I.D. blower
motor will continue to operate at the current speed for 60 or 90
seconds after the flames are extinguished .
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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
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-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.
If loss of flame occurs during a heating cycle, the control (IGN)
in the first
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
With the comfort control set to COOL and the fan set to AUTO,
the com pressor contactor (CC) and the indoor fan motor (IDM)
are energized.
The energized compressor contactor (CC) completes the cir cuit
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 comfort control fan set to ON, the indoor fan motor
(IDM) will continue to run regardless of compressor and con-
denser fan operation.