NOTE: Use AWG No. 18 color-coded copper thermostat wire
for lengths up to 100 ft. (30.5 M). For wire lengths over 100 ft.,
use AWG No. 16 wire.
The 24-v circuit contains an automotive-type, 3-amp. fuse
located on the control. Any direct shorts during installation,
service, or maintenance could cause this fuse to blow. If fuse
replacement is required, use ONLY a 3-amp. fuse of identical
size. (See Figure 40 or Figure 41)
See the Service and Technical Support manual for detailed
instructions on control wiring and setup,
Thermostats and Control Settings for
(F/G)9MXT Two-Stage Furnaces
A single-stage or two-stage heating and single-stage or
two-stage cooling thermostat may be used with the furnace.
Refer to typical thermostat wiring diagrams and the Sequence
of Operation section of the Service and Technical Support
manual for details on configuring the furnace control board.
Consult the thermostat installation instructions for specific
information about configuring the thermostat.
Thermostats and Control Settings for
(F/G)9MXE Single-Stage Furnaces
A single stage heating and single-stage or two-stage cooling
thermostat may be used with the furnace. Refer to typical
thermostat wiring diagrams and the Sequence of Operation
section of the Service and Technical Support manual for details
on configuring the furnace control board. Consult the
thermostat installation instructions for specific information about
configuring the thermostat.
Accessories (See Figure 39, Figure 40, and/or
Figure 41)
1. Electronic Air Cleaner (EAC)
Connect an accessory Electronic Air Cleaner (if used)
using 1/4-in female quick connect terminals to the two
mate 1/4-in quick-connect terminals on the control
board marked EAC-1 and EAC-2. The terminals are
rated for 115VAC, 1.0 amps maximum and are
energized during blower motor operation.
2. Humidifier (HUM)
(F/G)9MXT There are two humidifier outputs on the
furnace control. The 115 VAC HUM terminal is
energized when the Induced Draft Relay closes. The
24 VAC HUM terminal is energized when the low
pressure switch closes during a call for heat. Connect
an accessory 115 VAC accessory humidifier to the
HUM terminal and L2 on the furnace control. Connect
a 24 VAC humidifier to the 24 VAC HUM terminal and
C screw terminal strip on the control board thermostat
strip. (See Figure 40)
(F/G)gMXE The HUM 24 VAC terminal is a 24 VAC
output energized when the gas valve relay closes
during a call for heat.
NOTE: There is not a HUM 115V terminal on the single stage
ECM furnace control board. Available ONLY on the two-stage
ECM and PSC single-stage furnace control board.
Connect an accessory 24 VAC, 0.5 amp. Maximum (if
used) to the 1/4-in. mate quick-connect HUM 24 VAC
terminal and C screw terminal on the control board
thermostat strip. (See Figure 41)
NOTE: If the humidifier has its own 24 VAC power supply, an
isolation relay may be required. Connect the 24 VAC coil of the
isolation relay to the HUM 24 VAC and C screw terminal on the
control board thermostat strip. (See Figure 39)
Alternate Power Supplies
This furnace is designed to operate on a utility generated
power which has a smooth sinusoidat waveform. If the furnace
is to be operated on a generator or other alternate power
supply, the alternate power supply must produce a smooth
sinusoidal waveform for compatibility with furnace electronics.
The alternate power supply must generate the same voltage,
phase, and frequency (Hz) as shown in Table 11 or on the
furnace rating plate.
Power from an alternate power supply that non-sinusoidat may
damage the furnace or cause erratic furnace operation.
Contact the alternate power supply manufacturer for
specifications and details.
440 01 4001 08 Specifications subject to change without notice. 33
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