I understand Bryant Evolution systems and a certain Lennox,
(model G60UHV60C090X07) vary blower speed depending on,
I think, static pressure. For zoned systems, I believe these
units do not need bypass dampers. They can somehow sense
if one zone is open versus two or more, and then adjust blower
speed and CFM accordingly. I was hoping to determine whether
that sensing is done entirely by the blower motor electronics
or whether there is a sensor in the airstream somewhere and
maybe the main control board tells the blower motor to adjust.
Obviously, this knowledge would really help diagnosis in the event
a blower motor was responding inappropriately to static pressure.
For example, the motor slowing down to almost nothing every
time one of the zones opens and then speeds up when the
zone dampers are closed--I pulled the zone damper motor wires
in that case.
So this is not the typical ECM-motor-not-running problem. This motor
runs at various speeds. It just does not do it consistently. It USED
to do it fine, for years. Then it stopped. And then it supposedly started
working after I left the house when the homeowner called for
heat hours later.
Thank you for any enlightenment.