Air compressor trouble video
 

Here is a video (some of you have probably already seen this) of my old quincy air compressor. The unloader valve cycles but it can do this for a few minutes before it shuts down. It does NOT build up too much pressure. The diaphragm of the unloader looks fine, old but not cracked and seems like that part is actually working. Im starting to think it is the pressure switch but not sure and dont want to tear into it before i have a better idea of how or what might be the actual trouble.

https://youtu.be/xiPihdiys_g

Jim

Re: Air compressor trouble video
 

Hi Jim, does that air line connect, to an electrical box? You may have sticking contacts? Or the air cylinder inside is sticking. You should have a power cord going into the pressure switch electrical box, then wires or cord, going to the motor. Clear as mud? Google 220 volt air compressor wiring. Hope this helps!
Cheers, Neil.

Re: Air compressor trouble video
 

Sounds like maybe either the unloader/blow-off valve spring is weak, making it want to dump early? or the pressure switch is sticking so it doesn't cut out normally and has to vent?

I didn't see a gauge, but you sounded like it is struggling to get up to shop pressure somewhere 90-120 psi?

See if the valve up top has a screw adjuster somewhere to change the preload where it dumps? Or the pressure switch should have one or two to set motor kick in / kick out