Air Compressor Help

[sergechronos]

So, have a 60 gallon 5hp air compressor (the brand of which escapes me at the moment) which in the fall was working just fine for me. Fast forward to March and I go to start it up, and it doesn't want to run. If it does run at all, it basically surges between high and low after it hits 20psi. I tried replacing the pressure switch and the drain to no avail. Would like to avoid having to take it elsewhere to get it worked on as I spent on $300 on it, and I'm not sure it'd be worth the money to get it fixed vs just buying another one.

So long as the tank pressure is under 20psi, the compressor runs fine. Above 20psi, and it just keeps cycling between it's normal sound and something that sounds lower. I am hesitant to run it past that as I don't want to damage anything and it's certainly not something I've experienced before. Figured I'd check here before I went to go post in tool specific forums to try to find a cure. I'm assuming something internal to the electric motor is likely failing?

[anyonebutme]

check the belt tension?

[green-lantern]

check the belt tension?

does sort of sound like a pressure switch problem though. Might want to try and take it apart and look for corrosion/rust.

If you need that small compressor back until you get it figured out you can come by and pick it up.

[sergechronos]

I'll check the tension later today or tomorrow, haven't seen or heard it slip.

Something that occurs to me though: do these use a capacitor while running? I know that there's one they use to start, but if there's one while running and its gone bad, then once the compressor sees a load that could start the surging electrically (which then causes the mechanical surge I can actually hear.)

Shouldn't need that compressor Paul since most of my tear down stuff is done, its just body work I would like to use the compressor for. That little one would implode if I tried to run the DA on it for any real length of time.

[anyonebutme]

You won't hear it slip, it'll just run "slower". It can't make it too tight with their adjustment type, so as tight as possible. Capacitor is just for the start.

[sergechronos]

I'll get some more coffee in me, wrap up the bottom end of the short block and go give it a shot. See what happens.

[1stStealthN/A]

Did the compressor release the head pressure when it shuts off at max pressure? Does it continue to hiss air after it shuts off? If it does it is probably the tank check valve. If the belt is snug and the check valve is okay you may have a defective valve assembly in the head. If it has a difficult time and groans when starting it may be trying to start against tank pressure which also points to the tank check valve. Hope this helps.

[sergechronos]

Haven't run it up to max pressure yet, didn't want to damage anything with the way it was running.

Haven't tightened the belt yet. Hoping to pull it out of its closet to do that tomorrow. Back and shoulder have just been too uncooperative to try moving this heavy s.o.b.