Compressor capacitor motor won't start 1

[karlhirzel]

I have a small capacitor start compressor that when last I tried to use it, the motor sounds and looks like it is trying to turn over, but even with no air pressure to pump against won't rotate more than a couple of degrees, and will trip out the circuit breaker after only about 5 seconds. It has two capacitors, I assume one for starting and one for running. I took apart and do not detect any burned components or windings. How do I check to see if capacitors are working before I chuck it.

 

[ccjersey]

As I understand the rules of this forum, your "how to" question is not appropriate, though some of the regulars might take it on just for something to discuss.

More appropriate site

http://www.smokstak.com/forum/forumdisplay.php?f=6

 

[OperaHouse]

Ones first thought is always a bad capacitor, but my last several motors have been bad centrifical switches. Mechanical parts of these just fatigue. I've noticed many motors now use a standard microswitch that seems under rated. At least those are easy to replace.

 

[edison123]

Are you able to turn the shaft by hand ? May be it's stuck.

Please post more details like motor nameplate, cap sizes etc.

 

[karlhirzel]

This motor is from a Campbell Hausfield compressor. The nameplate states 15 F.L.A, 120 v, Model MC31800AV. It does turn over easily, I had the motor apart and the capacitor covers off and didn't smell anything. As to the centrifugal switch, how does it work and how might I test/evaluate it?

 

[OperaHouse]

The switch is normally closed. This provides power to a separate start up winding through the capacitor. Assume this is a single capacitor motor. With motor not connected to power, measure resistance across the capacitor. This will verify the connection through the switch, start winding and main motor winding.

A 100W lamp in series with the capacitor will do the same thing and also test the capacitor. Test no more than a couple seconds.

 

[karlhirzel]

This actually has a second capacitor which I would assume is a "running" capacitor, what is the function of this capacitor? Is it to reduce surges on the feed voltage due to the nature of this type of capacitor?

 

[waross]

It supplies the magnetizing current and so lowers the line current.
Your problem is most likely an open starting switch.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ccjersey]

http://www.pentairwater.com/pentekmotors/Assets/P8098TB_SMC_CSIR.pdf

The capacitors (both start and run) cause a phase shift between the current in the main and start windings. This increases torque available to start and maintain the load.

Without the start winding, there is no continuous torque, just an oscillation. Without the capacitors, the torque produced by the starting winding would be much lower.

 

[OperaHouse]

The larger value capacitor is the start.