SERVICE AND TECHNICAL SUPPORT MANUAL Gas Furnace: (F/G)9MVE
Specifications subject to change without notice.
440 04 4800 00 32
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
continuous−blower airflow.
When the thermostat “calls for low−cooling”, the blower
motor BLWM will switch to operate at low−cooling airflow.
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 BLWM will
operate an additional 90 seconds at high−cooling 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 additional 5
seconds, if no other function requires blower motor
BLWM operation.
6. Heat pump
See Figure 20 and Figure 21 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 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.
Component Self Test
Refer to page 18 for instructions.
Figure 18
Variable Speed Furnace with Single
Stage Air Conditioner
NOTE 9
Figure 19
Variable Speed Furnace with
Two−Stage Air Conditioner
L09F027
NOTE 9
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