Trane 4DCY4024 Installer's Manual page 26

Installer's Guide
Cooling Cycle:
With the comfort control set to COOL and the fan set to AUTO,
the thermostat will energize (Y/Y1), (G), and (O). These signals
will energize the compressor contactor (CC), the indoor blower
motor (IDM), and the switchover valve (SOV), respectively.
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 blower motor (IDM)
will operate as a result of the (G) signal. The thermostat will
continue to cycle the compressor with the indoor blower to
maintain the indoor temperature at the desired setpoint. With
the thermostat fan switch in the ON position, the indoor blower
motor (IDM) will continue to run regardless of compressor and
condenser fan operation.
*CONT802 and *CONT803 Operational Differences
from the above sequence:
NOTE: Unlike the *CONT402, these two controls will
not call for the furnace to operate when the outdoor
temperature is above the selected outdoor temperature
changeover point even if the heat pump capacity is
not enough to maintain the indoor temperature at the
desired heating setpoint. If it is anticipated that the
installer selected outdoor temperature changeover
point from heat pump to furnace must be set to a
temperature at or below where this occurs, then
the *CONT402 control must be used instead of the
*CONT802 and *CONT803 Comfort Controls.
These two controls are not able to cycle on second stage heat
in the same way as the *CONT402. The *CONT402 can cycle
the gas heat on and off to maintain the indoor temperature
at the desired heating setpoint without transitioning to heat
pump operation each cycle if the building load is relatively
high. These two controls will cycle on second stage heat by
alternating between gas heat and heat pump operation.
two controls may take up to 25 minutes to transition between
heat pump and gas operation.
These two controls require a field installed jumper wire
between the W1 and W2/X2 low voltage wires at the 4DCY4
unit since these two controls produce only a W1 output for
auxiliary heat. This jumper will result in low fire gas heating
for 10 minutes or for as long as W1 is present if less than
10 minutes during auxiliary heating. Then, if the W1 signal
is still present from the Comfort Control, the 4DCY4 unit will
transition automatically to high fire and operate on high fire
for the remaining duration of the call for auxiliary heat. During
Emergency Heat mode operation these two controls will first
energize X2 on a call for heat and will potentially energize W1
as well. In contrast, the *CONT402 Comfort Control will first
energize W1 on a call for Auxiliary or Emergency Heat mode
and will potentially energize W2 as well as required by the
building load.
Page 26
DEMAND DEFROST OPERATION
During the heating cycle, the outdoor coil may require a defrost
cycle which is determined by the demand defrost control (DFC).
This control continuously measures the outdoor coil temperature
(CBS) and the outdoor ambient temperature (ODS-B) and
calculates the difference or delta-T measurement. An initiate
delta-T is calculated based on the delta-T measurements
obtained after defrost terminates (when the outdoor coil should
be clear of frost). When the measured delta-T during heating
operation reaches the calculated initiate delta-T, the demand
defrost control (DFC) opens the circuit to the outdoor fan motor
(ODM) and energizes the switch-over valve (SOV), placing the
unit in the cooling mode to defrost the outdoor coil. The outdoor
coil temperature sensor (CBS) terminates the defrost cycle,
or times off after twelve, fifteen, or twenty minutes in defrost,
the (DFC) energizes the outdoor fan motor (ODM) and fifteen
seconds later de-energizes the (SOV), which returns the unit
to the heating mode. Supplementary gas heat is brought on to
control indoor temperature during the defrost cycle.
Safety Sequences
This product is equipped with the following devices.
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 excessive 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
These
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)
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 thermostat from ON to OFF for approximately
three seconds, then back ON.