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441 01 2121 01
input is turned ON when no dehumidify demand exists.
Once 24 vac is detected by the furnace control on the
DHUM input, the furnace control operates in dehumidi-
fy mode. If the DHUM input is low for more than 48
hours, the furnace control reverts back to non−dehu-
midify mode.
The cooling operation described in item 3. above also
applies to operation with a humidity sensing thermo-
stat. The exceptions are listed below:
a. Low Cooling−When the R−to−G−and−Y1 circuit is
closed and there is a demand for dehumidification,
the furnace blower motor BLWM will drop the
blower airflow to 86 percent of low−cooling airflow
which is the CF (continuous fan) selection as
shown in Figure 55.
b. High−Cooling−When the R−to−G−and−Y/Y2 circuit
is closed and there is a demand for dehumidifica-
tion, the furnace blower motor BLWM will drop the
blower airflow to 86 percent of high−cooling airflow.
High−cooling airflow is based on the A/C (air condi-
tioning) selection shown in Figure 55.
c. Cooling off−delay−When the “call for cooling” is
satisfied and there is a demand for dehumidifica-
tion, the cooling blower−off delay is decreased from
90 seconds to 5 seconds.
5. Continuous Blower Mode
When the R−to−G circuit is closed by the thermostat,
the blower motor BLWM will operate at continuous
blower airflow. Continuous blower airflow selection is
initially based on the CF (continuous fan) selection
shown in Figure 55. Factory default is shown in
Figure 55. Terminal EAC−1 is energized as long as the
blower motor BLWM is energized.
During a call for heat, the furnace control CPU will
transition the blower motor BLWM to continuous blower
airflow, low−heat airflow, or the mid−range airflow,
whichever is lowest. The blower motor BLWM will re-
main ON until the main burners ignite then shut OFF
and remain OFF for the blower−ON delay (45 seconds
in low−heat, and 25 seconds in high−heat), allowing
the furnace heat exchangers to heat up more quickly,
then restarts at the end of the blower−ON delay period
at low−heat or high−heat airflow, respectively.
The blower motor BLWM will revert to continuous−
blower airflow after the heating cycle is completed. In
high−heat, the furnace control CPU will drop the blower
motor BLWM to low−heat airflow during the selected
blower
−OFF delay period before transitioning to con-
tinuous−blower airflow.
When the thermostat “calls for low−cooling”, the blower
motor BLWM will switch to operate at low−cooling air-
flow. When the thermostat is satisfied, the blower motor
BLWM will operate an additional 90 seconds at low−
cooling airflow before transitioning back to continuous−
blower airflow.
When the thermostat “calls for high−cooling”, the
blower motor BLWM will operate at high cooling airflow.
When the thermostat is satisfied, the blower motor BL-
WM will operate an additional 90 seconds at high−cool-
ing airflow before transitioning back to continuous−
blower airflow. When the R−to−G circuit is opened, the
blower motor BLWM will continue operating for an addi-
tional 5 seconds, if no other function requires blower
motor BLWM operation.
NOTE: If the blower−off delay is set to the maximum, the
adjustable continuous−fan feature is locked (i.e., fan speed
cannot be changed from its current setting).
6. Heat pump
See Figure 29 − Figure 33 for thermostat connections.
When installed with a heat pump, the furnace control
automatically changes the timing sequence to avoid
long blower off times during demand defrost cycles.
Whenever W/W1 is energized along with Y1 or Y/Y2,
the furnace control CPU will transition to or bring on the
blower motor BLWM at cooling airflow, low−heat airflow,
or the mid−range airflow, whichever is lowest. The
blower motor BLWM will remain on until the main burn-
ers ignite then shut OFF and remain OFF for 25
seconds before coming back on at heating airflow.
When the W/W1 input signal disappears, the furnace
control begins a normal inducer post−purge period
while changing the blower airflow. If Y/Y2 input is still
energized the furnace control CPU will transition the
blower motor BLWM airflow to cooling airflow. If Y/Y2
input signal disappears and the Y1 input is still ener-
gized the furnace control CPU will transition the blower
motor BLWM to low−cooling airflow. If both the Y1 and
Y/Y2 signals disappear at the same time, the blower
motor BLWM will remain on at low−heat airflow for the
selected blower−OFF delay period. At the end of the
blower− OFF delay, the blower motor BLWM will shut
OFF unless G is still energized, in which case the
blower motor BLWM will operate at continuous blower
airflow.
7. Component test
The furnace features a component test system to help
diagnose a system problem in the case of a compon-
ent failure. To initiate the component test procedure,
ensure that there are no thermostat inputs to the con-
trol and all time delays have expired. Turn on setup
switch SW1−6. (See Figure 26)
NOTE: The component test feature will not operate if the
control is receiving any thermostat signals or until all time
delays have expired.
The component test sequence is as follows:
a. The furnace control CPU turns the inducer motor
ON at high
−heat speed and keeps it ON through
step c.
b. After waiting 10 seconds the furnace control CPU
turns the hot surface igniter ON for 15 seconds,
then OFF.
c. The furnace control CPU then turns the blower mo-
tor BLWM on at mid−range airflow for 15 seconds,
then OFF.
d. After shutting the blower motor OFF the furnace
control CPU switches the inducer to low−heat
speed for 10 seconds, then OFF.
NOTE: The EAC terminals are energized when the blower is
operating.
After the component test is completed, 1 or more status
codes (heartbeat, 2+5, or 4+1) will flash. See component test
section or Service Label (Figure 51) for explanation of status
codes.
NOTE: To repeat component test, turn setup switch SW1−6
to OFF and then back ON.
Wiring Diagram
Refer to wiring diagram Figure 56.
Troubleshooting
Refer to the service label. (See Figure 51—Service Label)
The Troubleshooting Guide (See Figure 57) can be a useful
tool in isolating furnace operation problems. Beginning with
the word “Start,” answer each question and follow the
appropriate arrow to the next item.
The Guide will help to identify the problem or failed
component. After replacing any component, verify correct
operation sequence.
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