Thanks for the post!

You've already ruled out a few things I would typically mention: extension cord, check valve (back pressure) and pressure switch contacts.

I would test the capacitors just to be safe, you can do this with a simple multi meter (grab one at Radio Shack or elsewhere for $20 if you don't have one already).

Otherwise, the Unloader Valve acting up on the pressure switch can certainly cause this problem. The problem now is that you can't turn the compressor on and pump it up to pressure to find out if the Unloader is working or not.

You can remove the valve from the pressure switch and look inside to see if the seal is damaged or not; many times you'll find an o-ring seal or plastic seal inside...it's probably damaged, or you could have debris inside.

You can try cleaning it or replacing the Unloader Valve, most are available separate from the Pressure Switch; we have a variety located at the below link:

www.mastertoolrepair.com/pressure-switch...lves-c-25_2_258.html

Just choose the one that visually looks like yours.

If the Unloader Valve seal is broken or damaged, then air will [probably] constantly bleed out of it, or it won't open when the unit shuts off like it's supposed to, to discharge the excess air in the line and off of the pump head. This can certainly cause a breaker to trip.

- MTR

I understand you don't want to put so much into this (than you already have), so I agree. Being the Unloader is pretty inexpensive, I'd give it a shot, though.

Hope it helps!

- MTR