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room thermostat, momentarily turn off the FAN switch or
push button on the room thermostat for 1- -3 seconds after
the blower motor BLWM is operating. The furnace control
CPU will shift the continuous- -blower speed from the fact-
ory setting of FAN to HEAT speed. Momentarily turning
off the FAN switch again at the thermostat will shift the
continuous- -blower speed from HEAT to COOL. Repeat-
ing the procedure will shift the continuous- -blower speed
from COOL to FAN speed. The selection can be changed
as many times as desired and is stored in the memory to be
automatically used following a power interruption.
5. Heat pump
(See Fig. 25 - - 32 for thermostat connections.) When in-
stalled with a heat pump, the furnace control automatically
changes the timing sequence to avoid long blower off
times during demand defrost cycles. When the R- -to- -
W- -and- -Y1 or R- -to- -W- -and- -Y1- -and- -G circuits are ener-
gized the furnace control CPU will switch to or 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 sig-
nal disappears, the furnace control begins a normal inducer
post- -purge period and the blower remains running at
HEAT speed for the selected blower- -OFF delay period
then switches to low- -cool speed (same speed as FAN). If
the R- -to- -W- -and- -Y1- -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- -Y1 signals disappear, leaving the G signal, the
blower motor BLWM will remain on for the selected
blower- -OFF delay period then switch to continuous- -
blower speed. When the R- -to- -W- -and- -Y/Y2, R- -to- -
W- -and- -Y/Y2- -and- -G, R- -to- -W- -and- -Y1- -and- - Y/Y2, or
R- -to- -W- - and- -Y1- -and- -Y/Y2- -and- -G circuits are ener-
gized the furnace control CPU will switch to or 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 sig-
nal 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/Y2- -and- -G or R- -to- -W- -and- -Y1- -and - -Y/Y2- -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/Y2 or R- -to- -W- -and- -
Y1- -and- -Y/Y2 signals disappear, leaving the G signal, the
blower motor BLWM will remain on for the selected
blower- -OFF delay period then switch to continuous
blower speed.
Wiring Diagrams
Refer to Fig. 54 for wiring diagram.
Troubleshooting
Refer to the service label. (See Fig. 50.) The Troubleshooting
Guide (See Fig. 55) 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.
47
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