Internal Operation; Blower Motor Components; Initial Power Up; Variable Speed Ecm Blower Motor - Lennox CBX40UHV Series Installation And Service Procedure

VARIABLE SPEED ECM BLOWER MOTOR

To Remove Blower From Unit: Remove wiring jack plug and
three screws and slide blower out.
Figure 13. Blower Motor (B3)
WARNING
During blower operation, the ECM motor emits energy
that may interfere with pacemaker operation. Interfer­
ence is reduced by both the sheet metal cabinet and dis­
tance.
The ECM (electronically commutated motor) communicates
with the air handler control via a 2-way serial connection. The
motor receives all necessary functional parameters from the
air handler control and does not rely on a factory program like
traditional variable speed motors. The wiring harness
connects the motor to the air handler control. See wiring
diagram regarding wiring harness. A solid‐state controller
is permanently attached to the motor. The controller is
primarily an AC to DC converter. Converted DC power is
used to drive the motor. The controller contains a
microprocessor which monitors varying conditions
inside the motor (such as motor workload). Because this
motor has a permanent magnet rotor it does not need
brushes like conventional DC motors]
Internal components are shown in figure 14. 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.
IMPORTANT
Earlier ECM motors used on other Lennox air handler
models are not interchangeable with motors used on the
CBX40UHV line.
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.
Blower Motor (B3)
All CBX40UHV blower motors use single phase power.
An external run capacitor is not used. The motor uses
permanently lubricated ball‐type bearings.
CONTROLLER
Figure 14. Blower Motor Components
The motor is controlled via serial communication between
the integrated control and the controller permanently
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.
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.
When B3 begins start‐up, the motor gently vibrates back and
forth for a moment. This is normal. During this time the
electronic controller is determining the exact position of the
rotor. Once the motor begins turning, the controller slowly
eases the motor up to speed (this is called "soft‐start"). The
motor may take as long as 60 seconds to reach full speed. If
the motor does not reach 200RPM within 13 seconds, the
motor shuts down. Then the motor will immediately attempt a
restart. The shutdown feature provides protection in case of a
frozen bearing or blocked blower wheel. The motor may
attempt to start eight times. If the motor does not start after the
eighth try, the controller locks out. Reset controller by
momentarily turning off power to unit.
Page 20
STATOR
(WINDINGS)
ROTOR

Internal Operation

Initial Power Up

Motor Start‐Up
BEARING
OUTPUT
SHAFT
CBX40UHV