Troubleshooting - Bryant 821T Installation, Start-Up, Operating And Service And Maintenance Instructions

6. Heat pump
See Fig. 29 - - 32 for thermostat connections.
When installed with a heat pump, the furnace control auto-
matically changes the timing sequence to avoid long blow-
er 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 mo-
tor BLWM at cooling airflow or low- -heat airflow, which-
ever 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 air-
flow. 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 ener-
gized 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.
7. Component test
The furnace features a component test system to help diag-
nose 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 Fig. 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 motor
BLWM on at 50 percent torque for 15 seconds, then
OFF.
d. After shutting the blower motor OFF the furnace con-
trol 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 11
or 25 will flash. See component test section or Service Label (Fig.
54) 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 Fig. 55.

Troubleshooting

Refer to the service label. (See Fig. 54—Service Label.)
The Troubleshooting Guide (See Fig. 59.) 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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