Air compressor quit

[JSanders10]

Bought used a couple years ago, my Porter Cable 24gal air compressor decides to quit working. I know little about air compressors but can fix most things if I am told what I need and what to do.

Power is good, but makes only a humming sound when powered on. I have confirmed it is not an electrical issue from the breaker or plug.

 

[repete]

I would check that 1) Your unloader valve is functioning correctly to allow the compressor to start without load on the unit. 2) power is good at startup (put a volt meter on the outlet when it is attempting to start. Not a check without load) 3) Any start/run capacitors are good.

Gregg

 

[JSanders10]

I would check that 1) Your unloader valve is functioning correctly to allow the compressor to start without load on the unit.

Gregg, thank you, is that the drain valve on the tank?

 

[repete]

It is a small valve located on the pressure control switch. When the compressor runs it pumps air into the tank. Where this air enters the tank (usually a copper line) there is a check valve that does not allow to only go in the direction of the tank. There will also be a small line that runs from this large tank fill line toward the pressure switch. The unloader valve drains the air from this line when the compressor cuts out so there is no load on the compressor head for the next start cycle.
Hope this makes sense...

 

[repete]

J, here is a simple no load test.
Drain the tank completely and see if the compressor starts, If it does then wait for it to build pressure until control switch shuts it of at high pressure. If the unloader valve and check valve are functioning correctly you will hear a air hiss for a second or two at shutoff draining the fil line.

If there is no hiss then valve is not unloading. If the hiss continues for an extended time then the check valve is defective.

Sorry my first post was not really clear on a test process.

 

[R134a]

Those motors need a capacitor to run. Hum with nothing else = high probability the cap is bad. You can verify its rating with a meter. Be sure to discharge it as a precaution before handling it.

 

[kenmac]

Is it direct drive, or belt driven ? If belt driven, take the belts off and see if the motor will run without a load

 

[71bronco]

Same thing happened to mine. I took the start capacitor off and googled the numbers on it and bought one from Amazon for about $10 to $15. Worked fine.

Jeff

 

[Tinhack]

Item 23 in your parts book.