Please help troubleshoot my compressor motor

[Tony Zona]

I assume the motor is bad on my 30-gallon Craftsman air compressor, but I don't know how to troubleshoot it.

The motor is 15 amp, 3450 rpm. 120 v AC.

I discovered a tripped circuit breaker when I went into the shop today, then narrowed it down to the compressor.

The filter is clean, just for the record.

When I plug the compressor in it runs for two or three seconds before tripping the breaker.

When this compressor ran normally a couple days ago it sounded like a huge vibrator until it reached cut-off pressure. It is not making that sound now when it runs for those couple seconds. I can spin the cooling fan by hand and it runs freely. I feel a little suction when I spin the wheel and hold my hand over the air intake.

That's what I'm facing. The compressor trips the 20-amp breaker, and it doesn't sound normal for the two seconds.

Can anybody advise me on what the problem is or how I can further troubleshoot? Thanks.


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[Ken Fitzgerald]

Tony, what is the model number of the compressor so I can try to find a wiring diagram?

[Jerry Bruette]

Maybe the unloader valve is stuck shut.

Compressors don't like to start under a load.

I think your unloader is the valve on the right side of the picture with the two pieces of tubing connected to it.

Good Luck.

[Myk Rian]

Start switch could be stuck.

[David L Morse]

...I discovered a tripped circuit breaker when I went into the shop today, ...

It sounds like the compressor was powered up when you left it and presumably cycled while you were gone and that's when it popped the breaker. Is that correct?

...When this compressor ran normally a couple days ago it sounded like a huge vibrator until it reached cut-off pressure...

Do you mean that it normally sounds like a huge vibrator or that it was just this one time?

...When I plug the compressor in it runs for two or three seconds before tripping the breaker....

Does the motor spin during those two or three seconds or does it just sit there and hum?


WARNING: When troubleshooting a motor be sure to give it 10 to 15 minutes to cool between attempts to start if it's popping a breaker. A 20A breaker can easily hold 40A or more for two to three seconds. The easiest way turn a motor with a minor problem into a charred wreck is to keep hitting reset in the hope that it will fix itself.

[Jerome Stanek]

Can you spin the motor by hand or is it locked up. We had one that the pump froze up

[Tony Zona]

Ken, model number is at the very top of this photo. (Where do you find the diagram?)

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David,
Yes it was powered, left on and cycling.

It normally sounds like a huge vibrator.

Yes, the motor spins.

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Myk, how do I tell if the start switch is stuck?
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[Malcolm McLeod]

Jerome is on the right track - - the trouble-shooting law-of-halves. If you can cut a potential problem in half 3-4 times, you have isolated the root cause.

If you can de-couple the motor from the compressor, try to run just the motor. It's not a perfect test, but if it runs, the compressor is probably the issue. If it doesn't run, dig into the motor.

The lack of perfection here is that the motor could run normally unloaded, but not loaded. Based on the description of the compressor's noises, my money says the motor is fine.

[Tony Zona]

Ken, model number is at the very top of this photo. (Where do you find the diagram?)
919.167310

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David,
Yes it was powered, left on and cycling.

It normally sounds like a huge vibrator.

Yes, the motor spins.
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Myk, how do I tell if the start switch is stuck?
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Jerry, how do I tell if that valve is stuck?
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Thanks for the leads, folks. Working with this is new to me.

[Ken Fitzgerald]

Tony, I typically just do a Google search using in this case "Craftsman 919.167310 manual" for the search phrase. Here's a link to a website that will allow you to download the manual. http://www.manualslib.com/products/C...0-2880582.html Just click on the manual title to step through it page by page.

Here's a link to Bob Vila. com where someone has similar symptoms. http://www.bobvila.com/posts/41656-6...1#.Vt8GMur2Z9A

Good luck!

[David L Morse]

Well, according to Ken's Bob Vila link this motor apparently has a somewhat flaky centrifugal switch design. Since you've shown your compressor spins easily by hand it's more likely to be the motor itself that's the issue. Your symptoms are consistent with a bad centrifugal switch (among other less likely things). That's where I'd start.

[Tony Zona]

I got into that this afternoon for a while. I tried to watch as I powered it on, but everything happens pretty quickly. Two seconds to see what's happen is not very long.

My centrifigal switch looks different than what was described. I'll get into it again tomorrow.

[Myk Rian]

My centrifigal switch looks different than what was described. I'll get into it again tomorrow.

Can you hear the switch make a click sound, when speeding up, and/or slowing down?

[Tony Zona]

It hits a speed instantly, more or less, then stops because the breaker tripped.

No clicks.

[Jerry Bruette]

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Jerry, how do I tell if that valve is stuck?
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Thanks for the leads, folks. Working with this is new to me.

Tony,

If you go to page 10 in the manual that Ken has linked to it shows the pressure release valve and the check valve to the tank. I suppose either of these could be malfunctioning. To check the check valve to the tank I'd just disconnect the tubing from the compressor head (the large tubing in the manual) and turn the compressor on. If it runs and stays running the check valve is the culprit, if it doesn't run you have to look elsewhere for the problem.

I don't know what the inside of the pressure release valve looks like, so I can't give any advice there, other than to look and see if you can remove/clean the valve.

Good Luck
Jerry