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There are a number of reasons why an air compressor will not cut off. Many of those reasons are written about on various pages on this website, however this page focuses specifically on the reasons why, and adds a link back to the forum page if you would like to ask a question about why an air compressor will not cut off.
In order for the air compressor to cut off, it is necessary for the pressure switch to “see” sufficient pressure to trip the pressure switch to off. When the pressure switch is off, power cannot flow to the motor, and the compressor will stop.
Therefore, the first reason why an air compressor will not cut off is because the pressure switch is not “seeing” the correct cut off pressure setting.
There are a number of reasons why an air compressor air pressure will not reach the cut off setting of the pressure switch and those are covered on other pages linked from the troubleshooting page on this site, www.about–air–compressors.com.
Typically these reasons have to do with failure of the compressor pump valves, high pressure valves, or pump gaskets. These issues have to be rectified in order for the compressor pump to drive sufficient air into the tank or air mains to raise the pressure to the point where the pressure switch and trip to off.
Another Reason An Air Compressor Will Not Cut Off
Another reason why an air compressor will not cut off is that the pressure switch itself is not reacting to the correct pressure setting in the switch, the pressure switch does not switch to off, power continues to flow to the compressor motor, and the air compressor continues to run until the pressure in the system reaches the cracking pressure of the pressure relief valve.
This latter scenario is a dangerous one and an air compressor that continuously builds pressure past the point of pressure switch cut off, to the point where the pressure relief valve cracks open venting higher pressure, should not be used again until the problem is resolved.
Typically this problem relates to the pressure switch points, the springs inside the pressure switch, or the diaphragm that shifts according to system pressure to trip the pressure switch off.
While it is possible to rebuild pressure switches, and there are a number of pages on this website relating to that, I personally couldn’t be bothered taking the time to find parts and rebuild the pressure switch that can be purchased online for somewhere between $15 and $50 depending on the type being used.
However, if rebuilding the switch is of interest to you, visit the site map page and scroll down to the link that takes you to the page about rebuilding pressure switches.
If after reading this article you still have questions about why an air compressor will not shut off please add a question below.
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Husky H1820 compressor builds pressure till it stalls at 130psi (it’s rated to 155), but keeps running. At this point it does not build any more pressure while it runs. If I shut it off, it doesn’t lose air pressure so I don’t think it has a leak.
7.5 hp, 230v, Campbell Hausfeld 80 gallon. Changed Pressure switch with new one part # provided by CH Tech, Unit still not shutting off when reaching 180# plus and popping relief valve. Must shut off power to unit to stop. CH Tech now says it’s the Magnetic Starter. Opened box, cannot see any visible signs of possible trouble. Your thoughts? Sick of throwing money and time at it for non solutions.
Hi-i have an odd problem with my Senco PC2001. It comes on fine and pumps up to the correct pressure (125psi or so), but then will partially run as pressure bleeds down. It kind of puffles as if it were trying to start with a bad/weak capacitor, but the cap tests fine, plus it comes on fully and pumps back up at the normal cut in pressure. I’ve opened up the switch, blown it out, hosed it with contact cleaner, and it still will intermittently partly run the motor before hitting the cut in pressure. If left on long enough… Read more »
That IS odd!
Can’t say I’ve ever seen or heard of this, but it sure sounds like you have a broken or very weak spring in the pressure switch.
I’d just replace it, as even if you found a broken spring you likely would not be able to source it. Plus those things are a beach to assemble.
After i posted that question i tinkered with it some more and think i figured it out. The pressure switch was wired backward—power wires were swapped with the motor wires at the terminals. I don’t really understand why it makes a difference or why it ran reversed like that to begin with…but put them back where they’re sposed to be and it doesnt seem to have the problem anymore. Dunno how that could have happened from the factory…though maybe previous owner screwed with it and that’s why i got it cheap at a pawn shop. Thanks again!
Hmm, that suggests there may be something shorting to ground, such that with the hot/neutral reversed, it powered the motor.
But, so long as it has a proper ground (green wire) all the way to a grounded receptacle, it shouldn’t be a problem with it wired correctly.
If you want to test that hypothesis, you can plug in to a GFCI outlet. If it ever trips, that’s what was going on, for sure. If it doesn’t then maybe whatever was shorting was cleared as a consequence to revering the wires.
Still really weird, though.
Thanks for the update!
I have an old Ridgid compressor. It’s worked flawlessly for 15 years. Now the pressure does not exceed 90psi and will not cut off. My nail gun stopped at the same time. I disconnected the nail gun but compressor does not reach my set psi (95). I do feel some small amount of air around the pump and regulator. I have not inspected the tank for cracks. Its a RIDGID OF45150A. Any help is appreciated.
Does the tank hold whatever pressure it gets to when you turn it off or unplug it? If not, you might have the somewhat rare problem of a bad unloader. If the tank holds, read on. As you know, this is an oilless pump. As often as not, the piston ring (some sort of plastic) is shot. So the bad news is that if the ring is torn/worn, you’ll have to improvise or junk it, as both the pump/motor assembly and the piston/cylinder assembly are out of stock and discontinued. You can probably use a mirror to look up the… Read more »
My compressor is brand new can the pressure switch be adjusted
That would depend on what machine you have and maybe which way you want to adjust it and why.
IOW, what is it and what’s it doing (or not)?