Air compressor will not stop

When an air compressor will not stop it could signal a problem with how the air compressor is pumping air into the compressor air tank.

Or, when an air compressor will not stop, it could also signal a major safety concern, and should be addressed immediately, before using the compressor again.

Compressor pumps up past cut out

If an air compressor runs, pumps air into the air tank, the tank pressure reaches the normal cut out pressure setting level, and the compressor continues to run and the pressure continues to build, this is a real problem! Eventually the PRV will let go, and the tank pressure should vent. The compressor will still run at this point though, and if it isn’t being monitored, it could run itself to death.

PRV doesn’t let go

The safety backup for the air compressor pressure switch is the PRV, the pressure relief valve.

The air compressor can pump air pressure into the tank to a level higher than the compressor is supposed to. If that pressure gets too high, there could be a major failure of a part, and if that compressor part is the tank, well, the results wouldn’t be good.

The PRV is factory set to a pressure higher than the cut out pressure of the pressure switch. If the pressure switch does not shut the compressor down at the normal cut out pressure setting, when the tank pressure reaches the PRV set point, the PRV opens and vents the air. If the PRV fails, my friend, you have a real serious problem!

If the compressor pumps air pressure past the normal cut out pressure setting, my advice is to not use the compressor until this is fixed.

Your compressor pressure switch should shut the compressor off

MDR 21 Condor Pressure switch

A typical pressure switch on your air compressor might be the Condor brand, similar to the one in the photo.

It is the compressor pressure switch that is supposed to shut the air compressor off when the tank pressure reaches the cut out pressure level. That pressure cut out level may be  in the 100 PSI through to 175 PSI level, depending on the brand and size of your air compressor.

The pressure switch reacts to the pressure in the tank and when that tank pressure reaches the cut out pressure setting the pressure switch trips to off, the power to the motor is cut, and the compressor stops. That is, if the pressure switch is working.

If the compressor continues to run past the cut out pressure setting then it is a pretty good bet that the pressure switch has failed. As far as I’m concerned, it is time for you to get a new compressor switch.

Replace the pressure switch

I know that finding after market parts for air compressors is hard, as so few of the stores that sell air compressors stock a comprehensive list of spares for the dozens of brands that they sell, and have sold, over the years.

When you are looking for a replacement pressure switch, as long as the replacement switch fits the mounting on your air compressor, if it connects properly to the existing unloader valve – or has an internal unloader valve – is the same voltage range as the existing and has the same cut in cut out pressure settings (or is adjustable) then you can use it.

It is not necessary to replace a pressure switch with exactly the same make and model. That is, unless your air compressor is under warranty. Using an off-brand part may void the warranty. But on the other hand, if the air compressor is under warranty, see the store where you bought it and give them the problem of replacing the switch. 🙂

That should take care of the case when an air compressor builds air pressure up past the cut out, and the compressor runs until the PRV lets go.

Air compressor will not stop – still

OK, there is another scenario where the air compressor will not stop and just keeps on running.

That is when the air compressor tank pressure will only pump up to a level that is below the pressure switch cut out setting.

That is to say, your air compressor starts OK – probably from an empty tank when you go to reuse it again, but instead of pumping up to the 100 – 175 PSI expected, the pressure in the tank only gets to 20 PSI, or 30 PSI or 80 PSI and levels out there. Even though the air compressor continues to run, the tank pressure refuses to increase.

Not correcting this problem can lead to self-destruction, or at the very least, overheating of your air compressor.

There are a number of reasons why this happens.

Failures on an air compressor that could cause this include:

  • intake valve failing
  • pressure valve failing
  • blown gasket inside pump
  • tank check valve is impeding flow
  • compressor leaks somewhere at the same rate that air is pumping into the tank

… to name just a few.

All of these will be discussed as a separate page linked under the Fixing Compressor Problems tab.

Comments or questions about this page can be made using the form below.

 

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Comments

  1. Don Curtis says:

    I have an older Ingersol rand F11G compressor that runs untill the prv opens. It sat for a couple years. I’ve finally got it running but it wont stop pressurizing. I’m not sure what the prv looks like….

    • Don, I couldn’t find a photo of the F11G so I’m not sure what the pressure switch looks like. I can say that typically, if an air compressor pressurizes air past the normal cut out pressure setting, that it’s the pressure switch that’s the problem. I would suspect a failed diaphragm if the pressure switch doesn’t shut off at normal cut out, or, welding of the points.

  2. roy pitt-jones says:

    I have a Mark RF 5-10 RD screw compressor. It gets to 10 bar, as set on the danfoss controller, then the electrical valve opens and dumps the pressure back into the inlet filter housing. The compressor continues to run, with the valve open. It gets down to 8, as the differential is set to 2 on the danfoss, and the valve closes, and the pressure goes back to 10, and the whole process repeats. It never stops.
    It is 10 yrs since this compressor was last used, and I do not remember it behaving this way. I’m sure it used to get to pressure and stop. Any ideas please?

    Just to add…. in addition to the Danfoss controller, which is switching the electrical valve, there is a second, fixed, pressure switch switch. Which one of these is supposed to actually stop the compressor?

    I will add some pics….

  3. Russell Perkins says:

    I think I sent this before. I have a 6gal Bostitch air compressor it supposed to cut off at a150psi but it releases the air down to about 100psi and keeps running over and over what do I need to fix it?

  4. I have a Craftsman 5 gal, 125 psi compressor. Runs continuously, gets some air in the tank and the gauges don’t register anything. Any ideas?

    • Bob, if the gauges don’t register anything, how are you finding out about the air in the tank. Are you saying that the compressor runs and runs and you get minimal pressure in the tank? If so, what have you checked, please?

  5. Eric Richards says:

    I own a WL651004AJ which is a Husky 17 gallon 5hp oil less compressor. I used your advice and replaced the pressure switch. The specs have it at 120psi turn on and a 150PSI cut off. After swapping it I turned on the compressor. The compressor ran for 15 minutes before I decided to run it off. The PSI would not reach above 95psi. I took off every connection and cleaned all the threads with a brush and wrapped new pipe tape on them and tightened them all back down.

    What do I look for now or replace to get this compressor working again?

  6. Kenneth Broussard says:

    My Dewalt air compressor d55146 will not build air pressure what could be wrong

    • What have you checked as per the list on this page, Kenneth? Is your compressor building pressure and blowing the PRV, is it running but not building pressure, what’s happening please?

  7. I’m having a problem with a Porter Cable CPF 6020 compressor. It runs continuously and will not shut off. After scanning the questions and answers here I don’t see an obvious answer to my problem.

    It will build pressure up to around to about 110 psi or a little higher. Once it reaches that pressure I can hear what sounds like air escaping from somewhere. It continues to run but doesn’t build additional pressure. If I shut the the compressor off no air leaks from anywhere and it maintains it’s 110-115 PSI pressure. If I turn it back on the motor stays off until some of the air in the tank is used. Once the pressure drops down to around 90 or so the motor restarts normally but then the cycle I just explained repeats itself. I have replaced the pressure switch with the a new OEM part and it didn’t help.

    I’m not sure what to look for.

  8. Peter Phillimore says:

    Hi i have just acquired an old air compressor, i have been told it works well but does not shut off just keeps going so you need to keep eye on it. I was wondering if you have seen anything like this one and advise how I can go about restoring it.attached photo.
    thanks
    pete

    • A venerable looking compressor, Peter. Hard to tell from the photo yet it looks like it’s got a pressure switch. If the air pressure continues to grow past the normal cut out, then it’s the pressure switch that’s likely at fault. If however, it runs and runs, but doesn’t build pressure much, those pages and what to do about these issues, can be found on the troubleshooting page on this site too.

  9. tim buckwell says:

    my compressor will not cut out what is the correct pressure to enable my compressor to cut out

    • Hi Tim. We note that you also posted to another page about this same issue. We have deleted the other posting. What have you checked on your compressor , as per the suggestions on this page, please? Not knowing the make or model of your compressor, we cannot tell you what the normal cut and cut out settings are. You can Google your make and model to likely find that info, and knowing that, can use that information to determine if it is your pressure switch that is the problem, or if you have other issues on the compressor.

  10. I bought a old heavy duty Sanborn compressor and the guy said it had a leak on the check valve which he assumed is the reason that it would pump up quickly to 100#-110# and not shut off but also not build any further.
    The pin hole in the pic I assume is there for a reason. That is where the air is coming from while pumping.
    When it is unplugged it will hold and maintain the tank pressure.
    Would this be weak valve discs or rings?

    • The photo helped, Steve. Thanks. Yup, this hole is there to act as the unloader for this compressor. It does bleed air all the time the compressor is running, and also bleeds air after the compressor stops, until all of the air over the piston is gone. If your tank check valve is not seating properly, air in the tank will continue to bleed out of this hole until your compressor cuts in to refill the tank. That the hole is not bleeding air when the compressor is off indicates to us that the compressor tank check valve is fine. You need to look at the pages about why compressors runs and don’t build air pressure. They will help understand why your air compressor plateaus at a pressure level below cut out, and as a result, will run continuously until it overheats on thermal and shuts down.

  11. hi
    i have the same problem that i am facing with my FIAC new silver 10 screw compressor that motors continues to run even after it the tank pressure is reached to 10 bar. The compressors doesn’t builds any more pressure but the motor doesn’t stops i have checked the pressure switch it is okay i have replaced the switch as well. kindly help what could be the issue?

    • Please review your manual or contact FIAC to determine if this model of compressor is designed to have the motor run continuously, but for the compressing of air to unload when the cut out pressure is reached. Rotary screw compressors often run continuously, loading and unloading as the pressure in the system varies. Since your compressor does run continuously despite the replacement of the pressure switch, our guess is that the Silver 10 Encapsulated Screw Compressor is one of those designed to run continuously.

  12. Hi there,

    I’ve a Wolf Air OL 185. It continuously runs up to 100psi when the PRV kicks in, but carries on running until I shut it off.
    If I use the air gun whilst it’s running at 100psi I get a quick blast of air but then the pressure dies down to nothing real quick. If I switch it off then exactly the same again – like it needs to build but then dies down again after a few blasts.
    Sometimes after the pressure has built up and I turn it off manually, use the air gun again a couple of times and then go switch it on again to build the pressure back up, it doesn’t turn on at all?
    Do I need a new switch ‘AND’ PRV, or should I just try the PRV first?

    Many thanks in advance.

    • What is the normal cut out pressure setting for your Wolf Air OL 185? We take it that it’s higher than the pressure at which the PRV lets go? If so, the PRV itself may be damaged or failing. Sometimes it gets contaminated by oil from the compressor, and starts to release early. Try rinsing it in solvent, and when dry, reinstalling to to test.

      As to a rapid drop in line pressure to your air gun, are you saying that there is plenty of air in the tank, but that, when you trigger the air gun, the supply to it drops too quickly? That suggests your air regulator has a problem.

      As to the compressor turning back on issue, if you are not using an extension cord, and this is a relatively new issue, and if you hear nothing when the pressure in the tank drops below the normal cut in, that suggests either the pressure switch has failed, or something in the line to the motor circuit has failed, and that often points to the start capacitor. If you use a multi-meter to test the motor side of the pressure switch to see if there is power flowing through it when the tank pressure is below cut in, that will tell you whether or not the switch has tripped to ON, and if so, that suggests that the switch is fine, and it’s a power problem farther along the motor circuit.

  13. I have triplex GA11C medical compressor with dryer.

    The compressor motor will not stop even the unloading pressure cut in, and when the dryer purge the 3 compressor run together and I have a plant fault alarm.

    I already increase and decrease the setting off cut in and cut out of pressure but still the compressor is still running.

    • We are not entirely sure what the compressor problem is, Edmon, and we cannot find detailed information about your GA11C compressor. Is it an Atlas Copco make?

      If the air compressor tank reaches cut out pressure and the compressor motor fails to stop, then we would look with a multi-meter to determine if power was still flowing through the pressure switch even though the tank pressure had bypassed the cut out pressure setting. If so, that points to a failed pressure switch.

  14. Hi,
    I have the same problem as above the motor keeps running until the PRV operates and the pressure switch does not stop the motor when it reaches the stated 8bar max pressure.
    I purchased a replacement pressure switch from the manufaturer this did not fix it , the manufacturer sent a second pressure switch but this did not fix it either, the motor still does not cut out.
    Could it be that the PRV is set too low and therefore operates before it has reached 8bar pressure instead of it’s stated 8.8bar pressure limit ?

    • At what pressure is the PRV letting go? Watch the tank gauge, and note when the PRV cracks to release air.

      • hi,
        according to the gauge just over 8bar,.

        • We don’t know the make of your air compressor Ally. If it’s a lower end, consumer model, the gauges used are not of the best quality, and may have a variance of 3-5+ PSI displayed different from the actual air pressure. If the compressor has a cut out of 8 bar, and the PRV cracks “just over 8 bar” then it is possible the PRV itself has failed. If yours has the ring in the end, when the tank pressure gets to the point where the PRV lets go, push in on the ring to hold the PRV shut, and let the compressor run until the tank pressure increases 1/2 a bar or so. It is possible that the tank pressure is not getting to the pressure switch cut out before the PRV lets go.

          • Hi,
            Thanks for your help, I have replaced the PRV and the compressor is working as it should.
            It’s a shame I had to fork out for an expensive pressure switch (£23.78) when all I needed was a cheap PRV (£2.99).
            So my advice to anyone with the same problem try replacing the PRV first before replacing the pressure switch.

            regards, Ally

          • You are welcome. We understand about the added expense yet, if you kept the old one, you now have a spare pressure switch.

  15. Kerry McDonald says:

    I have a Lincon 80 Gal air compressor that is feeding a commercial machine that requires 35psi of constant pressure. This demand is making the compressor to start every 3 minutes and I notice that there is still a lot more pressure in the tank that is available.

    How can I maximize the use of most of the pressure in the tank, if possible?

    If this is not possible, what other alternative can I do the reduce the cycling of the compressor?

    Someone suggested to attach a second 80 gal. tank. Will this work?

    Thank you.

    Kerry

    • If, for example, your air compressor has a cut in of 90 PSI, and a cutout of 125 PSI, every time the air pressure in the tank drops below the 90 PSI pressure level, the compressor will start Kerry.
      If you are pulling air from the tank to your machine at 35 PSI, and the compressor starts to rebuild pressure every 3 minutes, then you are consuming a significant quantity of air from an 80 gallon tank in that 3 minutes.
      You could adjust the cut in pressure of the compressor pressure switch downwards, so that the compressor would start less frequently, as long as, when the air compressor is running, your machine air consumption is less than the output of the compressor so that the air pressure in the tank will rise and shut off the compressor, as opposed to running and running and never stopping.
      You need to be aware of the duty cycle of your compressor too, to ensure that it does not run longer than is safe for it, from a temperature buildup standpoint. If the motor overheats, the compressor will shut down.
      You don’t indicate the HP of your compressor, nor do you indicate what the flow demand of your machine is at that 35 PSI.
      Adding a tank would give you an additional reservoir of pre-compressed air to be used before the tank pressure dropped to cut in, and that would help too, as long as you keep the duty cycle limitation in mind.

      • Kerry McDonald says:

        Thank you for that information. I am now better able to troubleshoot my problem.

        Keep up the good work.

  16. Tom Morgan says:

    We haven a eleven gal compressor that just recently continues to run constantly-I replaced the pressure switch but that did not fix the problem the compressor still runs. It never reaches the cut off pressure nor the PRV setting. The wiring is correct and there are no apparent air leaks. Can you help me please?

    • We’re not sure what more we can add to the page on this site, //fix-my-compressor.com/compressor-will-not-build-pressure/ , Tom. Maybe you can have a look at this page, and then add a comment telling us what you found? Also, if you do comment, please add the make and model number of your compressor. That always helps. By the way, if you kept the old pressure switch, then you now have a spare. The pressure switch was not part of the problem found when an air compressor runs and runs, and doesn’t build pressure past a certain point.

  17. i have two stage compressor ingersol rand , while reaching cut out pressure the compressor doesn’t get stop wheres it takes 5 second after the electrical conductor get chattered with large rough sound it stops . tell me the solution plz

    • We wish we knew the model number of your Ingersoll Rand compressor, so we cold have a look at the type of pressure switch yours has. If we are right, we suspect the chatter you hear is the points inside the switch, and that points to … perhaps, a switch diaphragm or spring issue. AT $30 – $50 or so for an off the shelf compressor pressure switch, that might be a relatively low price to pay to see if that solves the problem. If not, then you have a spare switch.

  18. I have a small compressor that won’t shut off. The pressure reaches the PRV is max. I replaced the pressure switch. It was a small 2 wire cylinder. I don’t think you can wire them wrong. Does this mean the new switch is faulty?

    • In our opinion, if the pressure in the compressor tank bypassed the normal cut out pressure setting, and the compressor runs and builds pressure to the point where the PRV valve lets go, and assuming that there are no other wiring issues (fused lead or point or some such ) then we would expect that it’s the pressure switch that is at fault.

  19. please help,
    I have a condor md 21 compressor switch on my compressor. The compressor runs great but the compressor keeps running until the PVR pops, the pressure lowers and the compressor just keeps on pumping. For some reason it will not cut out. I have taken apart the switch and to my surprise there is NO adjustment inside. There are two posts with springs at the top but the posts, have had green glue from the manufacturer on them so they cannot be adjusted. Can you help? Do I need a new switch? If so, how do I know which one I need.

    Mike

    • Though the switch has no adjustment, and many do not, that it lacks adjustment isn’t the problem. We suspect the points are welded shut. See the page about replacing the compressor pressure switch linked from the right navigation bar for some help.

      • Ok. So you are thinking the switch itself its bad and needs to be replaced? This was my thought too but i wasnt sure if my cut in and cut out setting were right. But apparently they cannot be adjusted. So where do i go about finding a new switch?

        • No shortage of suppliers for pressure switches on line, Mike. Use your browser to search for the same model and part number, or simply browse for compressor pressure switches. As noted on the replacing the pressure switch pages, there are criteria in selecting a new… essentially the new must mirror the old in a number of ways, all covered on those pages.

  20. Hi my problem is motor continues running not building up enough pressure have replaced reed valves althought problem still continue,the machine itself would not have done 1 hours work and is out of warranty.Air seems to be escaping from oil refill plug.

    • Well Dave, that air is escaping out of the oil refill plug is the clue that counts. If air is escaping out of the oil fill tube, that’s an indication that more air than normal – usually it’s just a bit and not noticeable – is getting by the piston seal and into the oil sump, and then out the fill tube. In our opinion you need to tear down the pump and replace the piston seals. You have torn the pump down to replace the valves. If you did not do so then, and you do tear the pump down to replace the piston seals, make sure you use a new gasket kit too.

  21. I TOO HAVE AN ISSUE WHERE I THOUGHT THE PRESSURE SWITCH WAS BAD AND REPLACED IT.
    IT STILL DOESNT STOP EVEN AFTER IT REACHES THE DESIRED PRESSURE. THE PRV KICKS ON AT THAT POINT. WHEN I TURN THE PRESSURE OFF, THE PRV STOPS EVENTUALLY

    • Well Bob, my experience is that if the pressure switch is not tripping to off when the tank pressure reaches the normal cut out, then the pressure switch has different cut in and cut out settings and may need adjustment, the pressure switch is wired incorrectly, or the pressure switch itself has failed. As the tank pressure drops, the diapghragm in the pressure switch moves accordingly, ultimately leading to the contacts in the switch to meet, thus starting the compressor motor. As the tank pressure rises, the diapghragm in the switch moves accordingly, and when the diapghragm, reacting to the increasing pressure in the compressor tank, forces the switch eletrical points apart at the normal cut out pressure level, then the compressor motor stops. When the pressure drops far enough in the tank again, the cycle repeats. If the motor continues to run past the cut out pressure setting and ultimately, until the PRV cracks open, then… you have a problem with the pressure switch.

      • Question then: I just replaced my pressure switch (120/150) due to the compressor not shutting off at 155+. Just installed exact replacement (non-adjustable devilbiss) and the pressure keeps going up – No shut off. Any thoughts?

        • Hello Andrew. In order for the compressor to keep running past the normal cut out pressure setting on the pressure switch, the pressure switch cannot be tripping to off at the cut out pressure.

          Assuming that the new Devilbiss compressor pressure switch has not failed, the only other thing that comes to mind is that it is wired incorrectly.

          Since the wiring is fairly straightforward, and I expect you mirrored what was the wiring on the original switch when you replaced it, then it must be that the pressure switch itself is not working.

          You say it’s got the same pressure settings as the old. I wonder if that’s so? Is the one below the pressure switch you purchased?

        • Andrew i had the same problem,new switch but i let run and when it hit 160 psi it shut down,at 160 psi

  22. my compressor wont turn off it keeps pumping till the PRV releases.
    Ive just put anew pressure switch and prv and it is still doing the same thing

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