Initial Power Up; Motor Start Up - Lennox G21Q3-40 Unit Information

The motor controller is driven by the VSP. The VSP re
ceives its demand (PWM signal or fixed 24 VAC or VDC sig
nal) from optional controls such as the Harmony zone con
trol system, Efficiency Plus Humidity Control (CCB1) or a
conventional thermostat.
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 adjust
ment. Blower rpm may be adjusted any amount in order to
maintain a constant cfm as shown in Blower Ratings
Tables. The amount of adjustment is determined by the in
cremental taps which are used and the amount of motor
loading sensed internally. Since the blower constantly ad
justs rpm to maintain a specified cfm, motor rpm is not
rated. Hence, the terms blower speed" and speed tap" in
this manual, on the unit wiring diagram and on blower B3
refer to blower cfm regardless of motor rpm.
When Harmony is used, speed taps are overridden and a
PWM signal generated by the Harmony controller continuous
ly varies motor speed based upon zone demands.

Initial Power Up

When line voltage is applied to B3, there will be a large in
rush 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.
The DC filter capacitors inside the controller are connected
electrically to the speed tap wires. The capacitors take
approximately 5 minutes to discharge when the disconnect
is opened. For this reason it is necessary to wait at least 5
minutes after turning off power to the unit before attempting
to change speed taps.
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 10 15 seconds to
reach full speed. If the motor does not reach 200rpm with
in 13 seconds, the motor shuts down. Then the motor will
immediately attempt a restart. The shutdown feature pro
vides 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 control
ler locks out. Reset controller by momentarily turning off
power to unit.
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DANGER
Disconnect power from unit and
wait at least five minutes to allow
capacitors to discharge before at
tempting to adjust motor speed tap
settings. Failure to wait may cause
personal injury or death.

Motor Start Up