Craftsman compressor will not go past 105 psi

by steven fox
(Seattle WA)

I have read through this website and it has been very helpful. Thank you. I have a Craftsman 150psi max compressor. It will build pressure (rather slowly) until it gets to about 105psi. The motor will keep running indefinitely but the pressure will not go any higher.


So far I have replaced the pressure switch, valve plate assembly, pump gaskets, and various o-rings and seals.

Nothing has worked. It holds pressure and I don't hear any leaks when I turn off the motor.

I can't feel any leaks while the motor is running.

The unit is plugged directly into the outlet and I run it alone on the circuit so it should not be under-powered. I do not feel air coming out of the intake.

The only other thing I can think of is the piston assembly in the pump. Could air be getting past the piston ring once it gets up to a certain pressure? I wanted to ask before I through any more money at this thing. Thanks in advance, Steve.

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Oct 20, 2014
Glad that a piston ring is the issue
by: Bill

It's a pain Steve, but good that you were able to diagnose the problem. A new compressor piston ring is a lot less expense than a new compressor, for sure.

Glad to have been what help I was.

We look forward to the updates.

Cheers,

Bill

Oct 20, 2014
Maintenance free!!
by: Steve

Thanks so much for your help and fast response, Bill. Now that I have read through this site I understand why the pressure switch is not the culprit here.

However, it was broken also, so it had to go.

What I failed to mention in my post is that this is an oil-less compressor (which I now know is not as "maintenance free" as belt driven unit). So I can't use your trick of pulling the oil plug, however that is good to remember for the future.

Since my last post I got curious and disassembled the pump farther. It turns out that the compression ring on the piston is destroyed. I am surprised that it even built to 105psi. So I am ordering a new compression ring, which is only a few bucks. Hopefully this is the last part it will need for now.

I will keep this site updated on the results.

Thanks again!

Oct 19, 2014
Craftsman compressor won't build enough pressure
by: Bill

Steven, I hope you didn't throw out the old pressure switch, as that isn't likely the problem.

You have jumped through a lot of hoops, and done almost everything right to diagnose the compressor problem.

If air is getting by the piston seals in sufficient quantity to stall the pressure build up at 105 PSI, you would feel that air coming out of the oil fill cap vent hole. If you aren't feeling air coming out of the oil fill tube, that likely isn't the issue.

The thing is, if the pump is pumping and pressure doesn't rise, it's not likely a compressor motor problem.

With an empty tank and the power off, pull the tank check valve to be sure it's working properly.

Tell me, was the pressure peak of 105 PSI the same pressure it stopped building pressure at before you changed out the valve and gaskets?

Bill

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