Trane 4DCL4024 Installer's Manual page 25

Cycling on 1st stage heat: When the thermostat cycles the
heat pump off, power is removed from (Y/Y1) and (G). If the
indoor blower delay is defeated in the unit, it is an installer
option for the thermostat to control the delay of the indoor
blower by using (G). If there is a thermostat controlled indoor
blower delay, the thermostat will turn (G) off after the delay
time set within the thermostat has elapsed.
Call for 2nd stage heating (gas) after 1st stage (heat
pump): If the heat pump capacity is not enough to handle the
building load, the heat pump is turned off and the gas heat is
brought on as the second stage of heat. The thermostat will
call for second stage heat by removing power from (Y/Y1) and
by powering (W1). (G) will remain energized for a minimum
of 2 minutes so that the transition to gas heat will not interrupt
indoor airflow.
(W1) from the thermostat signals the control module (IGN)
to run its self-check routine. After the control module has
verified that the pressure switch (PS) contacts are open, the
limit switch (TCO) contacts are closed, and the flame rollout
(RO) switch is closed, the induced draft blower (CFM) will be
energized on high speed for approximately 5 seconds.
After the induced draft blower (CFM) has come up to speed,
the control will verify that the pressure switch (PS) contacts
are closed and will switch the induced draft blower to low
speed for a 20 second prepurge. The gas valve (GV) is
energized in the first stage to permit gas flow and the spark
igniter (IP) is energized. The flame detector (FD) confirms that
ignition has been achieved within the 7 second trial period.
When the flame detector confirms that ignition has been
achieved, the delay to indoor blower ON period begins timing.
After approximately 45 seconds, the control module (IGN)
will take over control of the indoor blower motor (IDM). The
control module (IGN) will command the indoor blower to
operate at low speed throughout the heating cycle.
To maintain the indoor temperature at the desired
setpoint, the thermostat may operate the low fire gas
heating continuously or cycle low fire gas heating off and
on (cycling on 2nd stage heat).
Note: The 4DCL units are equipped with an outdoor
temperature switch to limit gas operation. For outdoor
temeratures above 40degrees, the outdoor temperature
switch and relays will substitute the W1 signal from the
thermostat and provide a Y/Y1 signal. The unit will then
operate in 1st stage heat (heat pump).
Cycling on 2nd stage heat: When the thermostat cycles
off during second stage heating, power will be removed
from (W1), the gas valve (GV) will close, and the flame will
extinguish. The induced draft blower (CFM) will continue to
run for a postpurge period of approximately 5 seconds before
shutting off. The indoor blower motor (IDM) will continue to
operate as the heat exchanger cools down (the delay is field
selectable for 45 or 90 seconds) before being turned off by
the control module.
NOTE: During gas heating operation, the indoor blower
is controlled by the normal sequence of gas furnace
operation, and not by the thermostat.
RELEASED 10/Aug/2020 16:34:00 GMT
Installer's Guide
Note that the *CONT402 may transition from second stage
heating (gas) to first stage (heat pump) and then back to
second stage heating (gas) instead of just cycling the gas
heat on and off if the building load is relatively low (see
the Transitioning from 2nd stage heating (gas) to 1st stage
(heat pump) section for a complete description).
Call for 3rd stage heating (gas) after 2nd stage (gas):
The thermostat adds (W2/X2) to (W1) signaling a call
for second stage heat. The induced draft motor (CFM) is
energized on high speed and the gas valve (GV) on second
stage. After approximately 30 seconds the control energizes
the indoor blower on high speed.
Cycling on 3rd stage heat: When the thermostat cycles
on third stage heating, power will be removed from (W2/X2)
and (W1) will remain powered. The control module (IGN) will
switch the gas valve (GV) to first stage and the induced draft
blower (CFM) to low speed. After approximately 30 seconds
the indoor blower motor is reduced to low speed.
NOTE: The 4DCL units are equipped with an outdoor
temperature switch to limit gas operation. For outdoor
temperatures above 40 degrees, the outdoor temperature
switch and relays will substitute the W1 signal from the
thermostat and provide a Y/Y1 signal. The unit will then
operate in 1st stage heat (heat pump).
NOTE: During gas heating operation, the indoor blower is
controlled by the normal sequence of gas furnace operation,
and not by the thermostat.
Transitioning from 3rd stage heating (gas) to 2nd stage
(gas):
Same sequence as cycling on 3rd stage heat (described
previously) except that the thermostat will make the transition
as described previously but will then begin to operate
continuously on second stage heating or will begin cycling on
second stage heating.
Transitioning from 2nd stage heating (gas) to 1st stage
(heat pump):
When the thermostat is cycling on second stage heat, the load
may decrease to the point where the thermostat determines
that the heat pump would have sufficient capacity to maintain
the indoor temperature at the desired setpoint. When this
occurs, power will be removed from (W1). This will cause the
gas valve (GV) to close and the control module to de-energize
the induced draft blower (CFM) after approximately 5 seconds
postpurge. The indoor blower motor (IDM) will continue to
operate (with no (G) signal) for the blower off period (45
or 90 seconds) while the heat exchanger cools down. At
approximately 45 seconds after power was removed from
(W1), the thermostat will apply power to (Y1). This powers the
compressor contactor (CC) which starts the outdoor fan motor
and compressor. The thermostat will also apply power to (G)
at this time so that the transition from gas heat to heat pump
will not interrupt indoor airflow. The purpose of the 45 second
delay is to give the indoor coil sufficient time to cool down
before resuming compressor operation.
Page 25