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period at HEAT speed.
When the thermostat "calls for cooling", the blower motor
BLWM will operate at COOL speed. When the thermostat is
satisfied, the blower motor BLWM will operate an additional
90 seconds on COOL speed before reverting back to
continuous-blower speed.
When the R-to-G circuit is opened, the blower motor BLWM
will continue operating for an additional 5 seconds, if no other
function requires blower motor BLWM operation.
4. Heat Pump
When installed with a heat pump, the furnace control auto-
matically changes the timing sequence to avoid long blower
off times during demand defrost cycles. When the R-to-W-
and-Y or R-to-W-and-Y-and-G circuits are energized the
furnace control CPU will continue to turn on the blower motor
BLWM at HEAT speed, and begin a heating cycle. The
blower motor BLWM will remain on until the end of the
prepurge period, then shut off for 24 seconds then come back
on at HEAT speed. When the W input signal disappears, the
furnace control begins a normal inducer post-purge period and
the blower switches to COOL speed after a 3 second delay. If
the R-to-W-and-Y-and-G signals disappear at the same time,
the blower motor BLWM will remain on for the selected
blower-OFF delay period. If the R-to-W-and-Y signals disap-
pear, leaving the G signal, the blower motor BLWM will
continue running the blower motor BLWM at HEAT speed
after the selected blower-OFF delay period is completed.
Step 4—Wiring Diagrams
Refer to Fig. 25 and 45 for wiring diagrams.
Step 5—Troubleshooting
Refer to the service label. (See Fig. 49—Service Label.)
The Troubleshooting Guide 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.
45
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