So it seems like the air compressor has been running for far too long. You watch it for a while, then realize that something is wrong. The air compressor will not shut off! After all, most air compressors turn off automatically.
Is this a problem with your air compressor? If your air compressor will not shut off, this is a serious issue that should be addressed before using the unit again. Read on… for the reasons why an air compressor will not shut off and remedies for that problem follow.
My air compressor will not shut off! What on earth is the problem? There are a number of scenarios that come to mind that might cause this compressor problem and they are explained fully below.
1. Issues With The Cut Out Pressure Level
The cut out pressure level is the pressure level above which the compressor will stop producing compressed air. The cut out pressure is basically used to indicate when the tank is full and ready to use. Once the pressure in the tank reaches the cut out pressure setting level, this indicates that the tank is pretty much full and ready to use.
Once there is a decrease in the pressure level, the compressor will start pumping air back into the tank. In some instances, however, there may be issues. Sometimes, the air compressor continues filling the tank after the cut off level is passed.
Let’s talk about these issues in more detail:
Tank Pressure Does Not Reach Cut Off: One of the issues, when an air compressor will not shut off, is that the tank pressure (displayed on the tank pressure gauge) never reaches the cut out setting to allow the pressure switch to trip to off which normally results in the pressure switch cutting power to the compressor motor and the air compressor shuts off.
Tank Pressure Stops Building: On other compressors, the tank pressure might reach a certain pressure level – also displayed on the tank gauge – and then the pressure in the tank stops building. The result? Again, the tank pressure never reaches the air compressor cut out pressure setting and the compressor cannot shut off.
Pressure Exceeds Cut Off: A third scenario is when the compressor runs, the tank pressure rises, then passes the normal cut out setting, and the compressor continues to run until the pressure relief valve (PVR) cracks open to vent the pressure. Normally, the PVR should balance the pressure inside the tank by releasing some of the pressure to the atmosphere. However, in some cases, the pressure is too much for the PVR to handle. Otherwise, it still doesn’t solve the problem if the PVR is working and balancing the pressure while the compressor is just increasing the pressure exponentially.
Here are some other issues normally involved when an air compressor will not shut off.
2. Issues With The Pressure Relief Valve
As we stated above, the pressure relief valve (PVR) is used to maintain just enough pressure inside the compressor tank. It does this by balancing the pressure inside the tank. In other words, it acts as an equalizer. This is why many people call it the safety back up of the air compressor.
Because of this, if there is ever a case where the PVR is activated and the pressure in the tank exceeds the cut out pressure, the PVR should let off excess pressure by opening a safety relief valve or vent called the pressure relief valve.
Of course, this only happens when the cut out pressure setting level fails to stop the compressor from working. If the PVR fails as well, you could have a serious issue.
If this ever happens, it’s important that you do not use the unit until you get a replacement and repair the device. PRVs are easy to find. This Control Devices ST Series Brass ASME Safety Valve, 125 psi Set Pressure, 1/4″ Male NPT is a good example.
Pressure Relief Valves Available On Amazon
1/4″ ASME Brass Safety Relief POP Off Valve, American Made, COMPRESSORS, Tanks (160 PSI)
Control Devices ST Series Brass ASME Safety Valve, 150 psi Set Pressure, 1/4″ Male NPT
3. Issues With The Pressure Switch
The pressure switch is very important because it turns off the air compressor whenever the tank pressure is high and reaches the cut out pressure setting level.
Because of this, you should try to be familiar with the PSI of your compressor. For example, the most common range is between 100 to 175 PSI. Once you know your PSI setting, you will know when it is exceeded as the pressure increases in the tank.
If you ever find that the pressure switch is not working, it’s important that you replace it. If your unit is still under warranty, then you should surely get it fixed by the manufacturer.
Otherwise,e you will need to source it yourself. If you cant find one that fits at your local store, you may be lucky enough to find one on Amazon. The Secbolt 90-120PSI Air Compressor Pressure Control Switch with Pressure Regulator Gauges Safety Valve Fittings Set is a quick example for those looking for switches within the 90 to 120 PSI range.
Pressure Release Switches Available On Amazon
New H/D Pressure switch for air compressor 95-125 w/Unloader
Heavy Duty Pressure Switch for Air Compressor 135-175 psi 26 Amp Single 1 Port
4. Air Compressor Will Not Shut Off – Is Gauge Broken?
The next thing to do is watch the tank pressure gauge as the compressor is running.
So, the gauge should rise steadily to the normal cut out pressure setting of the particular compressor. So how do you fix this air compressor not shutting off problem when the gauge is causing it?
If the tank gauge does not rise at all, that may be a symptom of a failed gauge, though this is unlikely. Still, if the regulator gauge works, swap it with the tank gauge, with the tank empty and the power off to the compressor.
After swapping, start the compressor again. If once again the tank gauge doesn’t move at all, then it’s likely not the gauge that is the problem, it is that the pump is not delivering air to the tank, and the tank pressure level cannot increase to cut out as a result. If however, you find that you have a guage problem, you can get a cheap one on Amazon, for example, this one is good value.
Air Compressor Gauges Available On Amazon
Control Devices ST Series Brass ASME Safety Valve, 150 psi Set Pressure, 1/4″ Male NPT
Secbolt 90-120PSI Air Compressor Pressure Control Switch with Pressure Regulator Gauges Safety Valve Fittings Set
5. Next, Check To See If Compressor Pump Is Actually Pumping
If the tank gauge is not moving at all, and the compressor motor is running, can you tell if the pump is pumping?
If the compressor hasn’t been running long enough for the pump to get too hot, or if it has, turn the compressor off and wait for it to cool, and then, resting a hand lightly on the top of the pump while the compressor motor is running should indicate if the pump is running and it’s not just the compressor motor running ineffectively.
If the pump isn’t running, then check any belts that connect the motor to the pump, or, if the compressor is direct drive, ensure that the coupling to the pump drive is still secure. If not, tighten it or tighten the belt if belt driven. Test again. If the pump still will not run it is likely that it has undergone a serious mechanical failure, and it’s time to take it apart to see what’s what.
More on this farther along. If you choose to replace it, there are several cheap portable options on Amazon,
More on this farther along. If you choose to replace it, there are several cheap portable options on Amazon, like this one;
EPAuto 12V DC Portable Air Compressor Pump, Digital Tire Inflator
NEW SCHULZ SINGLE STAGE CAST IRON AIR COMPRESSOR PUMP 2, 3 OR 5 HP + FREE FILTER
6. Tank Pressure Rises And Stops Before Cut Out Pressure Level
If the tank pressure rises and stops before it reaches the normal cut out pressure setting, yet the compressor motor and pump keeps running, that is a strong indicator that the pump itself may have a problem.
Pull the pump air intake filter and be sure that air is being pulled into the intake, and that air is not blowing back out. If air is escaping there, you’ll need to open the pump up and replace the intake valve.
Pull the line that runs from the pump to the tank and try, with a gloved finger, to try and stop the air flow out of the pump while it is running. If you can do this, odds are good that it’s the high-pressure valve that has a problem. Again, it will be necessary to take the pump apart to check.
If the compressor is oil lubed, and a lot of air is blowing out of the oil fill tube, that points to badly worn piston seals, and yes, you will need to disassemble the pump to effect repairs.
7. Compressor Does Not Stop And PRV Opens
If the pressure in the tank reaches the normal cut out setting and the compressor motor does not stop, then the pressure in the tank will continue to rise until the pressure relief valve lets go, venting the over pressure, and defusing a dangerous situation.
If this is happening with your air compressor, you should not use it again until the problem is corrected.
The fix is, typically, a replacement pressure switch. The pressure switch is supposed to cut power to the compressor motor when the cut out pressure setting is reached. That the air compressor will not shut off then, yet continues to run and the pressure in the tank continues to rise, indicates that the pressure switch has not tripped to off.
There is a diaphragm in the switch that may have failed, or, perhaps the points in the switch have fused, the latter often being caused by a short in the compressor wiring.
Regardless, if the compressor reaches a pressure level that blows the PRV, get the pressure switch looked at, fast. Preferably before you use the compressor again.
Is It Dangerous If My Air Compressor Will Not Shut Off?
If your compressor won’t shut off, you are flirting with a very dangerous situation. The compressor will keep compressing air into the tank until:
a) It can’t compress any more because there’s more pressure in the tank than the compressor head can overcome
b) The pressure relief valve opens to safely vent tank overpressure
c) Neither of the two above happens, and your compressor tank undergoes catastrophic failure, with significant risk to all and sundry around
We hope that the PRV works.
Regardless, if the compressor won’t shut off, you need a new pressure switch RIGHT NOW. Don’t delay. Your compressor is in trouble, and so could you be if you don’t replace the switch.
Conclusion On Why Your Air Compressor Will Not Shut Off
As discussed, there are several, but two main scenarios that should come to mind as to why an air compressor will not shut off.
One is that the pressure switch has failed, the air pressure in the compressor tank bypasses the normal cut out point of the compressor, the pressure continues to build, and eventually, (we hope) the PRV lets go to prevent over pressurization. This points to the pressure switch as the problem, and it should be replaced soonest!
The other scenario when the air compressor will not shut off is that the pressure in the tank reaches a pressure level below the normal cut out pressure level, and the pressure in the tank will go no further. Since the pressure in the tank stops rising, it never reaches the cut out pressure setting, and the pressure switch cannot react to the set point and shut the compressor off.
Finally On Air Compressors Which Keep Going
Sometimes, especially old compressors will need some extra force to the switch to turn it off. However, in some cases, there is an actual problem with the pumping g of air to the compressor tank or a similar issue that should clause a serious alarm. This problem should be addressed as quickly as possible using the methods outlined above.
It’s important to remember that even if you have a working air compressor, improper handling, age, and improper maintenance can cause serious issues like this.
So, over to you. These are the main scenarios why air compressors will not shut off. If these don’t help, feel free to leave a question below.
Thank you for lots of great information.
I have a 3 Gallon 135psi compress which I bought of Facebook marketplace. It was brand new with the plastic still on the gauges and not a single scratch. I didn’t test it before paying the dude… my fault.
Anyway, the compressor would run fine and the needles on the gauges kept climbing, then it started to get close to the red and all it the sudden, the PRV tripped. Scared the crap out of me but lucky it worked. I replaced the pressure switch and it is still doing the same thing. I am hoping that they didn’t send me a dud. Is there something else I can look at?
Hi Patrick, The pressure relief valve can lift if the pressure switch fails to shutoff the compressor at the cutout pressure setting. Your PRV seems OK as the needle increases. For this problem you can check the cut out pressure setting isin the normal working range. It should be less than the set value for PRV valve to lift.
You can also check for any restrictions in air flow that is causing the pressure to build up in the piping or hose connection, check the filters and drains too.
I have an air compressor it is having problem that not shutting at cut off pressure and pressure is not rising above 90 as I continue to use after few minutes it starts making noise as air is leaking and it also start getting hot.
What could be the reason?
Hi Sana, sometimes if the compressors efficiency is reduced it cannot reach above a certain level of pressure. If the pressure switch is working properly try changing the cut-out pressure setting. I hope this will resolve the problem.
Is my compressor too small for the work I’m doing? I use it to drive a very fine ‘drill’ held in a dental technicians hand piece for piercing and cutting thin wood. The compressor reaches the pressure , the motor cuts out, I start to drill and after a few minutes, five maximum, the motor cuts back in to refill the tank. Am I expecting too much of it or is there something else causing it to happen. Is there something I can adjust to increase the amount of time between cut out?
It’s a Bambi HT15.
I’ve attached an image of the type of work I do as I guess you’re already familiar with compressors!
Hi Vance, Try turning the screw in a clockwise direction at the pressure regulator. This will increase the cut-out setting however don’t increase the setting above the capacity of the tank otherwise PRV (pressure relief valve) will lift to drain the excess pressure. I hope that will resolve your problem for the compressor to meet the required capacity.
I have a Husky Whisper 68. It will not shut off. I have replaced everything electrical, ( on off switch, circuit board, pressure switch). I dont know what else it could be. Any suggestions would be great. Thanks
Chris, a bit more information is needed before nailing down the Husky compressor issue. It won’t shut off. I get that. But does the pressure in the tank grow so high that the PRV lets go, and still the compressor runs? Or, does the pressure in the tank never get to the normal pressure setting where the pressure switch shuts it off?
If it’s the first one, you’ve likely got a problem with the pressure switch not tripping off at the right setting. Could be the pressure switch isn’t set right, it hasn’t got the out of the box correct settings, or it’s wired so that even if the switch trips, power still flows.
The second issue points to a possible pump problem whereby everything is running, but the pump is not pumping sufficient air into the tank and the pressure never gets to the shut off level. Could be a gasket in the pump lets go at a certain pressure, a valve is stuck open or shut or broken, or the piston seals are so badly worn that all the air is blowing down into the oil sump (if it has one) and out the vent hole.
So, what is it?
I have a 80 gallon proair compressed put a new pressures switch on it still doesn’t shut off at the 175 cutoff any suggestions
Just to be sure, John, the compressor runs OK, builds pressure OK, tank pressure reaches and bypassed the pressure setting on the pressure switch, and the compressor keeps running until the PRV cracks open, and still runs? Are you 100% sure that the cut out on the switch is 175 PSI? Any change it might be higher since you bought a new one? Unfortunately, if the cut out is right, and the power to the motor still passes through the pressure switch after the tank pressure bypasses the switch cut out, then it has to be the switch that is not working. Please power off the compressor, dump the air to below cut in, pull the top off the switch, double check the wiring, make sure that the switch is rated for 240 volts, and power up the compressor. It should start, and at cut out pressure you should see and hear the contacts in the switch trip. If they do not, then it has to be the switch that is the issue.
I have a late 80’s Sears/craftsman 80 gallon 220. Just replaced the pressure switch with a new square d, factory shut off and cut ins. 95-125. The compressor still doesn’t shut off, builds pressure past the cut out and then the prv kicks in.
I’ve seen this question a few times, from a number of persons, Jed. Regardless of the age of the compressor, a new pressure switch should work. If it is still passing power to the motor when the tank pressure exceeds the pressure switch cut off point by 5 PSI or so, since general purpose compressor gauges aren’t that accurate) then either the pressure switch is not wired correctly, or the pressure switch has failed.
I have a napa air compressor that’s running constantly 80psi never shuts off. No leaks and I can shut it off manually. It did get hot the other day it was 100 outside. Compressor is mac 82-4278-vat I would appreciate any suggestions.
Hey Cheyenne. That your air compressor from NAPA is a MAC 82-4278-vat doesn’t have a specific bearing on this compressor issue, yet it’s always good to know the make and model, and for that I thank you. OK. So what’s what?
The normal stopping pressure of your air compressor is what… 125 PSI, maybe higher? So, if the tank pressure never gets to that pressure level, the compressor cannot shut off. Eventually it will shut down on thermal overload, or just fry and quit. Why is this happening? I am guessing that when it reaches 80 PSI and goes no higher, that isn’t because you are using air faster than it can make it? Rather, even if you aren’t using air, that’s the upper level the compressor gets too? If I’m right, then what I think is happening is this.
A small compressor typically has a a gasket of some sort in the pump head. This is all that separates the air that’s incoming from the air that’s heading to the tank after being compressed. Over time, and often due to high heat from running a compressor long periods, this gasket deteriorates… becomes less strong. When that happens the air coming out of the pump and heading for the tank, which is higher pressure than the air on the intake side of the gasket, can open a flow path through the gasket and into the intake air.
So, rather than having all the air heading down into the tank to increase pressure, air is blowing across the gasket hole, and back into the intake.
In your compressor, that hole in the gasket opens around 80 PSI. I’ve heard of others that leak between high and low pressure at varying pressures. If the pressure in your compressor is below that 80 PSI area, the gasket is still strong enough to separate the air streams.
So, I think you need a new gasket, and you can either try to find one as an OEM part on line, or, buy a high-heat sheet of gasket material and make your own. That’s what I think, anyway. Good luck with it, and maybe comment with what you found when you pulled the pump apart, as that’s what you’ll have to do to fix the problem.
One more thing. If there is a gasket and valve replacement kit available for this compressor, then I suggest you use all of it, and replace the gasket(s) and valve(s) plate rather than taking a chance just on the gasket being the sole problem.
Hi Compressor Man ‘
Can I ask a question regarding an electric compressor twin cylinder
which I have had 8 years trouble free until the diaphragm gave way on the pressure switch
* The old switch was 12 bar 175 PSI – I ordered a new one rated 10 bar 145-175
but now the engine wont shut down it keeps running then safety valve triggers letting the air out.
I live remote here in Western Australia & I need it running ‘ and no one out here does air compressor
work. My Switch has the Red Button on top of the black box ‘
Should I order again the 12 bar switch which I asked for but they sent me the 10 Bar Item
I am sure it only has 1 adjustment But I am Sure that adjustment doesn’t reset the cut off switch
Cheers in advance if you reply Trevor West Australia
If the pressure in the tank reaches the normal cut out pressure of the compressor, and the compressor doesn’t stop, that has to point to the fact that power is still flowing to, through, and on to the motor circuit. Why? If the compressor tank pressure switch reaches cut out pressure, the switch should trip off. What the pressure settings of the new switch versus the old are is really immaterial to the compressor running, as long as the cut out pressure is within the compressor pressure design parameters. So, either the new switch is bad, or the new switch has been wired so that power flows through it regardless of the pressure setting. I’d double check to be sure that the wiring to the switch and from the switch to the motor are correct.
Thanks I have been busy doing other jobs & will be trying again soon to find a cure
The wiring was very easy to install the new switch ,I followed the same colour code positions
Maybe it would be my luck I received a faulty part ‘so I will check into it
So thanks again for your reply .Trevor West Aust
My air compressor pumps up to the cut-out level of 135 and it cuts out, but immediately cuts-in, then cuts-out, then cuts-in. In summary it cycles between out and in until I turn it off. My pressure switch is new and is set at cut-in of 105 and cut-out of 135. I have a Baldor L1450 motor, a Brunner A212 compressor, a Powermate (Condor) – 034-0226RP pressure switch and a Cutler-Hammer – Model No. 6-200 on/off switch. I have it wired for 220. Any help would be appreciated!!!
If the new pressure switch has an issue, that might cause the symptoms, since the problem occurs, as you say, just at the cut out of the switch. Even if the air pressure in the tank just barely reached the cut out, once the switch trips to off, then the switch should not trip back on until the pressure drops to the cut in pressure setting. However, based on what you’ve written, I would check certainly the entire power circuit from switch to capacitor to motor and look for a loose connection, since the vibration just when the compressor reaches cut out might be enough to open a loose connection momentarily. If you do check it out, and have time, could you please let us know what you found?
Cannot adjust top end pressure without it sputtering. Fined tuned differential without success. Very frustrating. Have put new regulator on it. Seems like there is not enough pressure to lift the cutoff.
Dave, it seems to me that you are writing about a gasoline powered air compressor, rather than an electrically driven one? If so, then what I am thinking is that your motor unloader / throttle control is not functioning well, or is maladjusted. Is this an older compressor? If it was working well before, is the linkage for the throttle clean and easily moved? More information, including the make and model would help.
I got a used ingersoll rand air compressor. Its the 5hp 80 gallon. Had an electrician wire it for me. Had to replace the copper tube from the compressor to the tank.
Now the issue is it constantly runs and the pressure switch wont shut it off.
I replaced the switch with a brand new one from IR and it still does the same thing. Builds air to 150psi before the relief valve pops.
Daniel, I don’t believe the copper tube from the compressor to the tank is part of the issue. What you need to know is the at what pressure is the compressor supposed to come on, at what pressure is it supposed to go off, and if the new switch is the same as the old. It is possible that the new switch has a higher cut off pressure?
And, if not, you need to use a multi-meter to check the motor side of the pressure switch when the pressure in the tank moves by the cut out pressure by at least 5 PSI. If the switch is still sending power to the motor when the tank pressure is higher than the cut off of the switch, then the switch has to be the problem.
Either the cut off pressure is higher than the pressure relief valve setting, or the switch has a wiring issue when it was installed, or the switch has failed, as far as I’m concerned.
My compressor pressure switch is not turning off the compressor when pressure is achieved.
It compresses until the relief valve opens.
I have changed the pressure switch.
I have made sure lines are not plugged
What else can I do or check to isolate this issue?
Sorry, but if the air compressor tank pressure rises past the normal shut off pressure setting for the compressor, and the pressure switch doesn’t switch to off, cutting the power to the compressor motor, then it’s 99% sure that it’s the pressure switch at fault. For power to flow through the pressure switch to the motor, and the tank pressure rises to the stop power setting on the switch, it should trip to off, cutting power to the motor. If power is still flowing through the switch when pressure bypasses the normal shut off setting of the switch, then 1) the switch isn’t “seeing” the tank pressure, 2) somehow power is bypassing the switch and flowing directly to the motor (very unlikely) 3) the switch is wired incorrectly. I suspect it’s number 3 that’s the problem. Check where the power and motor wires connect to the terminals inside the switch and make sure they care connected correctly.
Hi There, The normal cut off as per pressure switch is 125 PSI. I noted that the tank reservoir gauge has been stopped at 110 PSI and it’s not reaching to the 125 PSI. There is not any leaks of air. It’s 5 gallon Power build HOT ROD compressor. It start to build the pressure with completely empty tank and stop increasing more than 110 PSI therefore it’s not reaching to the cut off point. Any suggestions please!
Yup. You’ll likely need a pump rebuild kit. I think your brand of compressor is Power Built like the image I uploaded, as opposed to Power Build?
If so, Google parts for Power Built compressor, include the model number, and since I found parts, I expect you will too. Good luck.
My compressor is not shutting off in auto mode unless I’m not turned off manually form pressure switch. Both gauges stops at 135 psi and not moving on to red zone and compressor stays ON but not shutting OFF. If I turned the switch ON in auto then it’s not turning ON unless I’m not decreasing some pressure from the tank. It turns ON again but not turning OFF automatically with pressure switch. I replaced the pressure switch but problem remains the same.
What is the normal cut out pressure of this compressor? Is it 135 PSI or higher? If the normal cut out pressure setting is higher than 135 PSI, and the tank pressure never reaches there, then it’s likely a valve plate, gasket or piston seal that is the problem and the compressor cannot reach the cut out to shut down normally.
If the compressor isn’t easily restarting, from what you have written, I suspect the unloader valve is not working properly.
That both gauges, tank and regulator, have the same reading suggests you are not lowering the pressure feed to your air tools. In some cases 135 PSI may be to much pressure!