Any HVAC experts? Problem with buzzing from blower motor

[JDMMAN]

Before jumping in and asking if I already Googled the topic, yes I have.

Furnace - 1990 Carrier 58GP-125-111DA, no run capacitor for the blower motor; yes this is a PSC motor and not an ECM.

Programmable thermostat kicks the burners on, however, when the temperature on the heat exchanger hits the threshold for the blower to kick on, there's a buzzing noise, the blower motor does not run/kick on (not without giving the blower cage a spin to overcome the initial inertia).

Oddly enough, the fan switch which is wired to "high" generally does turn over the blower motor and gets it to run. (ie. no buzzing).

Ended up taking out the blower motor assembly and found out it was an old GE Single Phase AC motor w/o the ability to add a run capacitor. I broke things apart and oiled the motor just in case. Reassembled and upon reconnecting everything, it spun over with the power turned on again. (direct fan switch)

Low and behold though, when the burners kicked on and try to turn on the blower motor, the same buzzing noise returned. I checked it wasn't a stuck relay on the control board, the buzzing was from the GE AC motor itself.

At this point in time, I'm not sure if it could be the selected speed for the thermostat triggered fan output is giving enough voltage (vs the highspeed setting) - which would mean a bad control board.

Or if it's just the GE AC motor getting long in the tooth and requires replacement.

Going to try changing the thermostat/temp triggered fan speed from low/med to med/high to see if that makes a difference.

Anyone have any ideas?

[captain134]

Just a thought but have you checked the voltage to the motor when that sequence is happening?

[JDMMAN]

Captain134 - unfortunately I don’t have access to my multimeter to check. That said, the furnace had worked fine last week without the same issue. So not sure what changed all of a sudden

[Darell_n]

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Captain134 - unfortunately I don’t have access to my multimeter to check. That said, the furnace had worked fine last week without the same issue. So not sure what changed all of a sudden

I would still upgrade it to a PSC motor from your shaded pole motor. The power savings will pay for it in a year or less if you kept the blower on. Or make the big jump up to an ECM.

[JDMMAN]

Just an update: ended up being a slight scratch to one of the parts inside the electric motor which caused the motor not to alternate phases. Replaced it with a PSC motor and it runs almost silently!