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31-5000729 Rev. 0
Blower Compartment
Each blower is statically and dynamically balanced as
an assembly before installation in the unit.
IMPORTANT
NF96DS units are equipped with a constant torque ECM
motor. It has a DC motor coupled to an electronic control
module both contained in the same motor housing. The
motor is programmed to provide constant torque at each of
the five selectable speed taps. Each tap requires 24 volts to
energize.
Input Voltage Requirements
The circuit is designed to be operated with AC voltage. To
enable a tap requires 12 to 33VAC. Expected current draw
will be less than 20mA.
Troubleshooting the Motor
Troubleshooting the motor is an easy process. Follow steps
below.
1.
Shut off power to unit.
2.
Remove input plugs P48 and P49 from motor. See
Figure 16 for troubleshooting procedure.
If correct voltage is present in tests 1 and 2 and motor is
not operating properly, replace motor. The motor is not field
repairable.
If replacing the indoor blower motor or blower wheel is
necessary, placement is critical. The blower wheel must
be centered in the blower housing as shown in Figure 13.
When replacing the indoor blower motor the set screw must
be aligned and tightened with the motor shaft as shown in
Figure 14.
Secondary Limit Controls
The secondary limit is located in the blower compartment
on the back side of the blower housing. See Figure 15.
When excess heat is sensed in the blower compartment,
the limit will open. If the limit is open, the furnace control
energizes the supply air blower and closes the gas valve.
The limit automatically resets when unit temperature returns
to normal. The secondary limit cannot be adjusted.
Figure 13. Blower Wheel Replacement
Center Blower Wheel
in Blower Housing
Figure 14.
Set Screw
Housing Hub
ALIGN AND TIGHTEN SET SCREW WITH
FLAT SIDE OF MOTOR SHAFT
Motor
Shaft
Figure 15. Secondary Limit Control
Secondary Limits
