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31-5000724 Rev. 0
Indoor Blower Motor
Figure 7.
During blower operation, the ECM motor emits
energy that may interfere with pacemaker operation.
Interference is reduced by both the sheet metal cabinet
and distance.
WARNING
The NF97DM line uses three different motor sizes; 1/2
hp, 3/4 hp and 1hp. The motor communicates with the
integrated control via a 2-way serial connection. The motor
receives all necessary functional parameters from the
integrated control and does not rely on a factory program
like traditional variable speed motors. NF97DM units use a
three-phase, electronically controlled D.C. brushless motor
(controller converts single phase a.c. to three phase D.C.),
with a permanentmagnet-type rotor (Figure 8). Because
this motor has a permanent magnet rotor it does not need
brushes like conventional D.C. motors.
Internal components are shown in Figure 8. The stator
windings are split into three poles which are electrically
connected to the controller. This arrangement allows motor
windings to turn on and off in sequence by the controller.
Earlier ECM motors used on other GE Appliances
furnace models are not interchangeable with motors
used on the NF97DM furnace line.
IMPORTANT
A solid-state controller is permanently attached to the
motor. The controller is primarily an A.C. to D.C. converter.
Converted D.C. power is used to drive the motor. The
controller contains a microprocessor which monitors
varying conditions inside the motor (such as motor
workload).
STATOR
(WINDINGS)
OUTPUT
SHAFT
BEARING
Figure 8. Blower Motor Components
The controller uses sensing devices to sense what position
the rotor is in at any given time. By sensing the position of
the rotor and then switching the motor windings on and off
in sequence, the rotor shaft turns the blower.
All NF97DM blower motors use single phase power.
An external run capacitor is not used. The motor uses
permanently lubricated ball-type bearings.
Internal Operation
The motor is controlled via serial communication between
the integrated control on the furnace and the controller
attached to the motor shell. The messages sent back
and forth between the two controls serve to communicate
rotational direction, demand, motor size, current draw,
torque, and rpm, among other variables.
Motor rpm is continually adjusted internally to maintain
constant static pressure against the blower wheel. The
controller monitors the static work load on the motor
and motor amp-draw to determine the amount of rpm
adjustment. Blower rpm may be adjusted any amount
in order to maintain a constant cfm as shown in Blower
Ratings Tables. The cfm remains relatively stable over a
broad range of static pressure. Since the blower constantly
adjusts rpm to maintain a specified cfm, motor rpm is not
rated. Hence, the terms “cool speed”, “heat speed” or
“speed tap” in this manual, on the unit wiring diagram and
on blower B3, refer to blower cfm regardless of motor rpm.
Initial Power Up
When line voltage is applied to B3, there will be a large
inrush of power lasting less than 1/4 second. This inrush
charges a bank of DC filter capacitors inside the controller.
If the disconnect switch is bounced when the disconnect is
closed, the disconnect contacts may become welded. Try
not to bounce the disconnect switch when applying power
to the unit.