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12. Blower Motor
IMPORTANT
Each blower is statically and dynamically balanced
as an assembly before installation in the unit.
ML180DFE 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
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 13 for troubleshooting procedure.
NOTE -
Figure 13 is typical ignition control illustration.
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 10.
When replacing the indoor blower motor the set screw
must be aligned and tightened with the motor shaft as
shown in figure 11.
13. Secondary Limit Controls
The secondary limit is located in the blower compartment
on the back side of the blower housing. See figure 12.
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 re
-
turns to normal. The secondary limit cannot be adjusted.
Center Blower Wheel
in Blower Housing
BLOWER WHEEL REPLACEMENT
FIGURE 10
Set Screw
Housing Hub
ALIGN AND TIGHTEN SET SCREW WITH
FLAT SIDE OF MOTOR SHAFT
Motor
Shaft
FIGURE 11
SECONDARY LIMIT CONTROL
Blower Assembly
Secondary Limit
FIGURE 12
