SERVICE AND TECHNICAL SUPPORT MANUAL
Gas Furnace: (F/G)9MXT
Specifications subject to change without notice.
440 04 4321 02
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(same speed as LO HEAT), and begin a lowheat 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 LO HEAT speed. When the W/W1 input
signal disappears, the furnace control begins a normal
inducer postpurge period and the blower remains
running at LO HEAT speed. If the Rto
W/W1andY1andG signals disappear at the same
time, the blower motor BLWM will remain on for the
selected heatoff delay period. If the
RtoW/W1andY1 signals disappear, leaving the G
signal, the blower motor BLWM will remain on for the
selected heatoff delay period then switch to
continuousblower speed.
When the RtoW/W1andY/Y2, RtoW/W1and
Y/Y2 andG, RtoW/W1andY1andY/Y2, or
RtoW/W1and Y1andY/Y2andG circuits are
energized the furnace control CPU will switch to or turn
on the blower motor BLWM at COOL speed, and begin a
highheat 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 HI HEAT speed. When
the W/W1 input signal disappears, the furnace control
begins a normal inducer postpurge period and the
blower switches to COOL speed after a 3 second delay.
If the RtoW/W1andY/Y2andG or
RtoW/W1andY1and Y/Y2andG signals
disappear at the same time, the blower motor BLWM will
remain on for the selected heatoff delay period. If the
RtoW/W1andY/Y2 or RtoW/W1
andY1andY/Y2 signals disappear, leaving the G
signal, the blower motor BLWM will remain on for the
selected heatoff delay period then switch to
continuousblower speed.
Component Self Test
Refer to page 13 for instructions.
Figure 17
TwoStage Furnace with SingleSpeed
Air Conditioner
Figure 18
TwoStage Furnace with TwoStage Air
Conditioner
Figure 19
TwoStage Furnace with SingleStage
Heat Pump (Dual Fuel)
