Heat Pump Defrost; Component Test - Bryant 355CAV A Series Troubleshooting Manual

desired and is stored in the memory to be automatically
used following a power interruption.
8.

HEAT PUMP DEFROST

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 midrange airflow, whichever is
lowest. The blower motor BLWM will remain on until the
main burners 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
energized 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.
9.

COMPONENT TEST

The furnace features a component test system to help diagnose
a system problem in the case of a component failure. To initiate
the component test procedure, ensure that there are no
thermostat inputs to the control and all time delays have
expired. Turn on setup switch SW1-6. (See Appendix A)
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 IDM ON
at medium 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 motor
BLWM on at midrange airflow for 15 seconds, then OFF.
d. After shutting the blower motor OFF the furnace control
CPU shuts the inducer motor IDM OFF.
Note: The EAC terminals are energized when the blower is
operating.
After the component test is completed, 1 or more status codes
(11, 25, 41, or 42) will flash. See Service Label on blower
access panel or Service/Status Code Instructions for explanation
of status codes.
Note: To repeat component test, turn setup switch SW1-6 to
OFF and then back ON.
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