About 1.5 years ago I replace the blower motor on a 25 + yo american standard residential furnace. It is a basic GF unit with a 1/3 HP motor mounted on the blower cage driving the blower via belt. Checked balance on the blower, oiled bearings, checked startup and running current on the motor, installed some shock isolators on the cage frame - all appeared OK.
The motor replacement was a Dayton with the exact same motor p/n as the existing motor....somehow I don't believe the existing was the original motor...but anyway....
Recently got a call back and owner said motor 'sometimes hums' on startup. Of course, when I went there, it didn't 'hum.' Checked starting and running current - within spec. I then realized that there was no starting capacitor in the unit - motor is across the 110vac line with a relay contact. Seemed a little strange but not out of the ordinary. Attempted to verify if it should have a starting capacitor but the wiring diagram on the front panel had deteriorated, making it unreadable. Starting relay was solid with no chatter.
It seems the the motor is dying - true? Could I have just gotten a bad motor that is dying after 1.5 yrs of heating and cooling service?
And now I am questioning if there should be a starting capacitor to increase the starting torque. The current motor seems to start fine - a little groan under the load but comes up to speed quickly. ALso wondering if maybe the motor should be a 1/2 HP.
Yea, the entire unit should be replaced - the heat exchanger is thin but serviceable. They are an elderly couple and don't want to put the money into it.....
So, thoughts on if the motor is dying or other reasons for the hum that is intermittent?