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Run capacitor?

P

PJH

Well-known Member
Westinghouse motor #321P591

Is there a way to tell if an electric motor needs a run capacitor to operate? About 15 years ago I replaced a blower motor that was getting a little noisy. The replacement motor has a run capacitor. I put the old motor on a shelf and now I have forgotten what little I once knew about it. There is no mention of a capacitor on the motor label. It has five wires - black, white, red, yellow and blue. The red, yellow and blue wires are taped up but not connected. It is a four speed motor, and I assume these taped wires would change the speed. The motor runs on the black and white wires, but it seems to get hotter than it should. I ran it for about ten minutes on my workbench, and it got nearly too hot to hold my hand on. It would run cooler in the blower, I would think.

Thanks for any advice.
 

What is the nameplate current how much current is the motor drawing ?
Just about any AC induction motor will have its running current reduced when caps are used to bring the power factor to 1.0 .
 
If there are not 2 brown leads, the cap is inside the motor. If it started and ran the cap must be inside.

Looking up the specs by the model, though I could not find a wiring diagram, I did see that it is an "air over" motor, which means it needs the air flow from an attached fan blade to keep it cool.

If you can find the full load amps, which will be different for each speed, running it without a load it should be well below the FLA rating.
 
Never saw a blower motor without a cap. It's been too long (crs) but there is a formula to find the cap size by using the volts x amps drawn compared to the label fla. Mabie Bob or another HVAC tech will remember. Most of the older blower motors I dealt with used a 10mf cap, but 7.5 was fairly common too. Really big blowers could have a 20.
 
(quoted from post at 08:11:17 10/28/20) The old motor without the brown leads is a shaded pole motor. It does not use a capacitor. Instead of capacitor, it uses shading rings to create the phase shift.
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ld 1960 furnace used blower without cap. Still have wiring diagram.
 
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