Are you having trouble with your air compressor not shutting off when it reaches cut-off pressure? You’re not alone, it’s one of the top troubleshooting questions we get on this website.
I’ve pulled together some of the most common reasons why your air compressor may not be shutting off, along with a series of top reader questions and responses giving help to troubleshoot compressors that just won’t stop!
Table of Contents
- Air Compressors Shutting Off
- Why Air Compressor Won’t Shut Off – Most Common Reasons
- FAQs (Frequently Asked Questions)
- Reader Questions and Responses
Air Compressors Shutting Off
Air compressors generally need time to cool after they work hard, hence why most are given a duty cycle rating. The duty cycle rating indicates the amount of rest time the compressor needs during its cycle time. For example, a compressor with a 75% duty cycle would need 15 minutes of rest in every 1-hour working cycle. To learn more, visit our air compressor duty cycle guide!
Air compressors should automatically shut off at the maximum cut-out pressure, let’s say 140 PSI, where the pressure switch would trip and the compressor turns off to prevent overpressurization. If this doesn’t happen, then there is something wrong with your compressor, and you may risk exceeding the duty cycle.
This means that if your compressor won’t shut off, it may need more than just a quick fix; you might have to wait for the machine’s internal parts to cool down before being able to try again. This is especially true if you use an oil-free compressor because these machines require less cooling time than other compressors. However, if waiting doesn’t work- something more serious may be wrong.
Why Air Compressor Won’t Shut Off – Most Common Reasons
- Air leaks
- Pressure switch problems
- Pressure relief valve failure
- Underpowered extension cord
- Motor problems
- Dirty filters
- Broken air gauges
Above, are some of the most common reasons why your air compressor may not be shutting off. Let’s take a look at these in more detail!
Air Leaks Causing Air Compressor Not Shutting Off
Air compressors have a cut-out pressure setting as already explained. The cut-out level is the pressure that an air compressor is supposed to stop producing additional compressed air. It works so that your air compressor knows when the tank is full only when the cut-out pressure has been reached.
Under normal operation, when the air pressure reaches a set level the pressure regulator bleeds some of the air off, which causes a decrease in pressure. Then, the air compressor will turn on again and resume pumping air back into the tank until it is full again.
Sometimes, an air compressor will continue to fill the tank after the cut-off level has been reached due to the potential that there is an air leak in the system. You must confirm whether or not there is a leak by listening for hissing sounds around the whole system or looking for holes in the side of the tank. It may be possible to fix leaks with special equipment.
However, another cause of the compressor not shutting off after reaching cut-out leaves your motor running which makes it so your air compressor won’t turn off. This causes the tank pressure to rise beyond the normal cut-out setting.
Pressure Switch Problems Causing Air Compressor Not Shutting Off
The pressure switch is a very important component of an air compressor. The pressure switch is a mechanical device that uses air pressure and electricity to control the operation of an air compressor. It’s a relatively simple mechanism that closes a circuit to power the motor if the system is below its set pressure level.
They allow you to set the cut-in and cut-out pressures of the compressed air system. If for some reason your compressor will not shut off, it could be that you have a faulty pressure switch that is not switching when the cut-out pressure is reached.
It is best to learn how to replace your pressure switch, as they’re typically inexpensive, as long as you purchase the right one. We have a number of pressure switch-related articles available on our site that might help you with this problem:
- Air Compressor Pressure Switch Troubleshooting & Buying Guide
- How to Replace An Air Compressor Pressure Switch
- How to Adjust Air Compressor Pressure Switch Control Valve
Pressure Relief Valve Failure Causing Air Compressor Not Shutting Off
Every air compressor has a PRV (Pressure Relief Valve) that will open to vent the pressure. During normal operation, the PRV is designed to balance the pressure inside the tank by releasing some of the pressure into the atmosphere.
In some instances, unfortunately, the PRV does not work as intended. If it gets stuck closed and the compressor motor keeps running, worst case the tank could eventually explode. The PRV could also become stuck open, which will prevent the tank from being able to reach its cut-out pressure, causing an air compressor to not turn off.
The pressure relief valve is used to maintain pressure balance inside the compressor tank and it could be worn out, damaged, or stuck. The valve is responsible for balancing the pressure inside the tank, if it is unable to do so then your air compressor may not shut off. You should inspect your pressure relief valve to see if it is stuck open, allowing gas to flow out when it shouldn’t.
For more information on this, visit our PRVs keep leaking – Air Compressor Pressure Relief Valve Leaking guide!
Underpowered Extension Cord Causing Air Compressor Not Shutting Off
It should be common knowledge that extension cords are unable to provide sufficient power for air compressors. If you need to work further from the wall socket, it is generally recommended to increase the length of the air hose rather than using an extension cord.
It’s possible that the use of an extension cord is hampering your air compressor’s performance, blocking it from being able to reach the cut-out pressure and thus causing the air compressor to not shut off. The simple solution here is to stop using the extension cord.
Motor Problems Causing Air Compressor Not Shutting Off
If the pressure inside your tank rises but then stops before it reaches the set cut-out pressure, but your compressor motor continues to run, then it is more than likely that you have compressor motor problems or a problem with the pump itself.
The next step is to remove the air inlet filter and confirm that no air is coming out of it if this is the case. If there is air coming out of your air compressor’s air intake, you will need to replace the air intake valve. Check this by removing the line that runs from the pump to the tank and using your hand to prevent the airflow out of the pump while it is running.
If you are able to do that, then your air compressor’s high-pressure valve is the air compressor’s problem. Visit our air compressor blowing air out intake guide. If you have an oil-lubricated air compressor and you notice air blowing out of the oil fill tube, that indicates your piston seals are worn out.
Dirty Filters Causing Air Compressor Not Shutting Off
It’s possible that your compressed air system’s filters are becoming clogged, affecting airflow and leading to your air compressor not shutting down. For this reason, you should inspect all filters and change any that need it due to dirt/debris buildup.
Broken Air Gauges Causing Air Compressor Not Shutting Off
A broken air gauge is another common problem that could cause an air compressor to not turn off. When it’s working, the pressure gauge will steadily rise until it reaches the compressor’s cut-out setting.
If the tank air gauge doesn’t rise, or it rises a little and then stops even when the compressor is still running, then it’s likely that you have a bad gauge. You should try turning the compressor off and listening for any air that may be leaking from the gauge or one of its connections.
FAQs (Frequently Asked Questions)
Yes, air compressors that are rated with a 100% duty cycle and for continuous use, are capable of running at constant pressure and flow. It’s dangerous to run your air compressor continuously if it is not rated for it, as it can lead to premature wear and tear.
An air compressor should shut off once the pressure within the tank reaches the set cut-out pressure on the pressure switch. When the compressor reaches its set cut-out pressure, the air compressor turns off to prevent overpressurization. If this doesn’t happen, then there is something wrong with your air compressor!
To turn off your air compressor, you can either flick a switch on the compressor’s pressure switch or remove the compressor from its power source. After doing so, it is important to drain all air from the system to ensure that no condensation is allowed to build up.
If your Craftsman air compressor won’t shut off, it is likely you have a faulty pressure switch that needs replacing, or the pressure relief valve is stuck in an open position, releasing air into the atmosphere and blocking your Craftsman compressor from reaching its cut-out pressure.
Reader Questions and Responses
My Air Compressor Won’t Stop Running
My compressor will not stop running. It builds up the pressure but keeps on running. I think that it needs a new regulator but I am not sure.
What you don’t say is if the pressure in the tank reaches and bypasses the cut-out pressure point.
If the compressor keeps running, and the pressure in the tank passes the cut-out point, then eventually your PRV is going to operate to vent pressure inside the tank before it reaches a dangerous level.
If the PRV is sized correctly, then it will vent air faster than the compressor can compress it, so ultimately all of the air in the tank will vent safely.
Your compressor, however, will continue to run since it would appear as though your pressure switch has failed, and since the unit can’t ever reach cut-out, it will eventually self-destruct.
If it’s the above scenario, then in my opinion your compressor has a serious situation with your compressor, and you should stop using it until you get it fixed. If the PRV fails too, there could be a dangerous over-pressure issue.
For the above, I suspect that the pressure switch may be at fault.
If, on the other hand, your compressor reaches a pressure point BELOW the normal cut-out pressure point, and the compressor keeps running but the air pressure doesn’t pass this point (say 70 PSI for example), then it’s not the pressure switch. That typically points to a valve or cylinder problem then.
Either way, your compressor will do itself serious damage if it runs past its duty cycle or over-pressurizes.
Hope this helps…
Compressor Won’t Shut Off and Pressure Won’t Build – Compressor Keeps Running
I have a sears air compressor that builds pressure up to 60 psi and keeps running but builds no more pressure. It used to build pressure up to 120 psi and then shut off until the pressure would drop.
When a compressor is running it’s pumping air into the tank, and when the pressure in that tank reaches the cut-out pressure setting, the pressure switch trips and the compressor stops.
In your case, as I understand it, the compressor cuts in at the low-pressure point, and pressure starts to build in the tank until it hits around 60 PSI, and then, even though the compressor keeps running, the pressure won’t build further.
First off, eliminate any leaks. It’s hard to hear a leak when a compressor is running, and it may be a small leak that the compressor can overcome until it hits that 60 PSI range, and then the leak intensifies and the compressor can’t get past that pressure.
If you’ve got no leaks, then it would seem reasonable that the air seals are worn to the point that the pressure can’t get past the 60 PSI point due to a blowback between the piston and cylinder wall.
Compressor Motor Won’t Turn Off Keeps Trying To Run When Full of Air
The motor won’t turn off keeps trying to run when full of air
If the compressor motor is still running after the air pressure in the tank reaches the normal cut-out air pressure level, then look to your pressure switch first as the source of the compressor problem.
If the air pressure in the tank doesn’t reach the normal cut-out pressure level, and since then the air compressor can’t shut off as the pressure never reaches the cut-out pressure level, then look to the intake valve or internal gasket leak as the possible source of the problem.
If the air pressure is bypassing the normal cut-out, I recommend that you get the pressure switch looked at or replaced before using the compressor again.
Compressor Won’t Shut Off Automatically? Air Compressor Keeps Running
With Switch set on automatic no matter what pressure I have the regulator set on the Campbell Hausfeld air compressor never cuts off until I manually turn it to the off position…..The compressor is a 20-gallon tank, 5.0 HP, 135 max. p.s.i.
Mike, I am having a bit of trouble understanding your terminology.
The switch that’s on “automatic” is the pressure switch setting, yes?
Is the regulator you refer to the one with which you adjust the downstream pressure to the airline and air tools? If so, that regulator has nothing to do with whether or not the air compressor cuts in or out.
That function, compressor ON and OFF is the job of the pressure switch, and if that switch is set to automatic, and the compressor runs until the tank pressure bypasses the normal shut-off pressure setting, then it’s a good bet that the pressure switch has an issue. You may need to replace it.
Air Compressor Cut Off Not Working
The compressor cuts on and builds pressure and does not cut off.
Changed pressure switch and the problem still exists?
What is the next thing to check?
The first thing is what’s the make a model of the compressor, please? Any chance you can upload a photo or two as well?
What pressure does the tank gauge get to before it doesn’t build any further and you shut down the compressor?
Does this happen every time you turn on the compressor?
If you drain the tank to zero and start the compressor again, does it do the same thing?
Can you feel around the air intake filter (assuming your compressor has one) and tell me if there is air puffing back out as the compressor is running?
Please provide the additional information, and identify the compressor.
Bostitch CAP 60 Will Not Shut Off?
I have a Bostitch cap60p-of that will keep building pressure after 135 psi and won’t shut off.
I have to shut it off manually. What part do I need to order for it?
The pressure switch is the device that turns the air compressor on at the cut-in pressure level and is supposed to shut your air compressor off at the cut-out pressure level.
If the air compressor tank pressure exceeds the normal cut-out setting of that pressure switch, then that suggests strongly that your pressure switch has failed and you need a new switch right away.
If, however, the air pressure in the tank never gets to the normal cut-out pressure setting of your pressure switch, that’s another issue.
Rather than retype all the info here, please see the troubleshooting page and the links to the page about why air compressors run on but do not build air pressure.
Bostitch Will Not Turn Off?
My Bostitch 150 psi oil-free air compressor will not turn off it kicks the on switch back on.
When it builds up pressure my Bostitch 150 psi oil-free air compressor will not allow me to shut off the compressor without plugging it out.
Worse than this the knob which allows me to control the amount of pressure released to sink nails deeper, will not stay it seems as if it is stripped.
What can I do to resolve these problems?
Hi Jeff. Are you saying that your air compressor starts, builds pressure in the tank, the air pressure in the tank passes the normal cut-out pressure, and the compressor keeps running?
If that is the case, does the compressor blow off the PRV?
When you set the downstream air pressure level with the regulator, are you saying that, if for example, you had set the pressure at 80 PSI for the nailer, the pressure gauge on the regulator shows a higher pressure?
Please provide a bit more info in a comment here so I can follow the thread.
Hi Bill the pressure builds to 120 psi and then stops. While it is filling if I try to push them off the switch the compressor kicks it back on.
The knob that controls the pressure I can fire a nail at seems to be stripped.
So, the cut-out pressure is 120 PSI, and the compressor will stop at that pressure? If you turn the switch off before the pressure reaches that 120 PSI and the switch pops back on, I suspect the switch is pooched. However, to ease the maintenance issue, let the compressor reach 120 PSI and stop automatically, or pull the plug when you’ve had enough. Either that or get the switch checked out.
You didn’t answer me about the reading on the regulator gauge. If the knob is stripped from the inside (this is possible) it’s time for a new regulator. Try pushing the knob in or pulling it out and see if it connects that way. Some regulators are built so that the knob can be disconnected internally by pulling or pushing the knob. If that doesn’t do anything, and you cannot adjust the downstream pressure, time for a new regulator.
Bostitch Will Not Go Past 100 PSI and Never Gets to Cut Off Pressure
I just replace the valve head with a newer style head from the CAP60PB-OF (mine is the CAP60P-OF) due to a broken valve flap.
Now it gets to about 128lbs and stops building pressure but keeps running.
The piston ring appeared to not have excessive wear.
Sounds as though you might have a gasket issue, Shawn.
Did you replace the gaskets when you replaced the valve plate?
If not, you likely need to. If so, you may have a crimp or weakened area that lets go when the pressure gets to the 128 PSI, and then the air just cycles back and forth in the head.
Craftsman 106.153784 Squeaks and Shuts Off
Model # 106.153784 sears compressor oil-driven will power on for about a minute pressure only reaches 30psi compressor rated at 150psi.
After a minute I hear a loud squeaking sound coming from the flywheel/pump area then it just stops while squeaking.
Daniel… check the belt tension and alignment first, please. That may not be the problem, but let’s eliminate that as the source.
What I surmise from your post is that as the pressure in the tank builds, the pump has to work harder to get air into the tank. As a result, the motor has to work harder too.
If the pump bogs down to the point where the motor cannot cycle it, the motor will overheat and go off on safety.
With the tank empty, remove, inspect/and clean the tank check valve. Again, this may not be the cause of the issue, but let’s get it out of the way.
Assuming that it is not the motor that is squeaking, suggesting that the motor itself is the problem, I am guessing that you may have a valve problem in the pump, that’s back-loading the pump and overloading the motor.
If you run the compressor with the line from the pump head off, I suspect it will run with no issues, right?
After you put the line back on, pull the pump intake filter and feel if the air is being pulled in strongly as the compressor runs.
If so, that would suggest that the issue is the high-pressure valve, and that means a pump tear down and valve replacement.
It ended being the belt tension. I unbolted the motor and slid it as far to the side as possible, making the belt tighter.
Thanks for taking the time to help me. God bless.
Bostitch CAP1512 Air Compressor Will Not Shut Off
I have a Bostitch CAP1512 air compressor. It will not shut off at 150 lbs and the safety valve keeps popping, says Mike Mercier.
If my memory serves… and that’s debatable for sure, I think I’ve read or seen this issue pop up before, Mike.
Good that the PRV is working and protecting you from catastrophic overpressure, but I sure wouldn’t rely on that as my only option.
So, since the symptom certainly points to the pressure switch as having failed, and since the pressure switch for the Bostitch CAP1512 is readily available, it was me, I’d be changing out the pressure switch before I used the compressor again.
It’s not a difficult repair since there are only two wires on the switch. Get a new switch, thread out the old, thread in the new, and attach the same wires to the two terminals. If the new switch isn’t part of a bad batch, your compressor should be back in business.
Give us a heads up about how that worked out for you, will you? Thanks.
Campbell Hausfeld Compressor Won’t Shut Off On Automatic?
With Switch set on automatic, no matter what pressure I have the regulator set on the Campbell Hausfeld air compressor never cuts off until I manually turn it to the off position… The compressor is a 20-gallon tank, 5.0 HP, 135 max. p.s.i.
The pressure switch turns the compressor on and off. The regulator adjusts the air pressure flowing down the airline. The two are not connected in terms of compressor operation.
If the switch, on automatic, is not turning the compressor off, and the tank pressure reaches the normal cut-out pressure for that compressor, then I’d be looking at getting a new compressor pressure switch.
WL-6701 Won’t Shut Off – Air Compressor Keeps Running
1. Air compressor won’t shut off. When I turn it on it builds up the air, but it won’t kick off or stop running.
2. The knob on the tank drain broke off. How can I go about getting a new knob and changing it out, or something?
The WL-6701 compressor has been discontinued. You might download the manual – WL6700 Series manual here and see if the contact info there brings any benefit.
As to the tank drain, expect to have to remove the whole thing and replace it with another. If you google compressor tank drain, you will find many. Pick one that suits you.
Campbell Hausfeld Model WL651500AJ Not Shutting Off – Why Does My Air Compressor Keep Running?
The compressor gets up to 175psi and the air release valve will push loose and let the air out causing the compressor to keep running.
How much psi is regular for the compressor to stop at? And what can I do? Why does my compressor keep running?
I believe the cut-out is 150 PSI. If the compressor continues to build pressure past that point, it’s time to replace the pressure switch.
WL610001AJ Campbell Hausfeld Air Compressor Won’t Shut Off
WL610001AJ Campbell Hausfeld Air Compressor won’t shut off. I used to turn the regulator adjustment knob as it reached 100psi and then it would shut down ( I think it is called a regulator adjustment knob), and the unit would turn off and turn back on as I used my tools.
Now it just keeps running. it builds pressure fine, but no matter which way I turn the regulator knob, it just keeps running. I only allow it to get to 110 psi as it states it is 125 psi maximum.
The other thing I notice is that after it gets to say 11psi and I pull the plug, release some air pressure (say down to 80psi), and then go to plug it in again, instead of running, it sounds like to motor is bound up and just hums and the lights in the garage on the same circuit dim as though the breaker is about to trip.
I noticed that there seems to be a release valve that connects from the pressure switch to the tank, and if I manually push the switch it releases a little air, and then if I plug it in, it starts right up again.
Do I have two separate issues??
Any help is appreciated.
Yeah, Mike, it sounds like you’ve got a few things going on with your Campbell Hausfeld Air Compressor.
First off, read the page on this site about pressure switches. These are the devices that control the on/off of your air compressor, not the air regulator. Adjusting the air regulator will do nothing for the turn on or turn off of any air compressor.
Please read the page on air regulators too to get a better understanding of how they work. This will give you a good grounding on this important piece of compressor equipment.
As to the lugging on startup, that’s probably covered by the information on the unloader valve page, so have a look at that. If the unloader isn’t working there’s an additional load on the motor, and it may not be able to overcome that to start or run properly.
If the unloader is OK, and nothing is new in the power supply to the compressor, it’s time to check the motor capacitor(s). There’s a page on this site to explain how to do that.
Then, if you’re still not sure, the troubleshooting page on why air compressors won’t start will give you some more things to check.
When you’re done, post a comment here telling us what you found, please.
Air Is Forced Out of Prv on My Husky Air Compressor
It all started with air leaking from the unloader, at the pressure switch. I purchased a new pressure switch. A new unloader assembly was included. I replaced the old switch & installed the new unloader.
I started the compressor & let the tank fill. When the tank was full, the pressure switch would not trip (shut off) as it was supposed to. Instead, the PVR opened. However, no leak was detected at any point in the unloader assembly.
I disassembled the check valve assembly & found a bad check valve.
So, I replaced the compressor’s check valve. Again, after filling the tank, the PVR opened again. And no leak was detected.
I’m about ready to pull my hair out. Can anyone shed some light on this?
Sorry, you had to buy a new pressure switch.
Compressed air blowing out the unloader valve when the compressor is running usually means the unloader valve has failed. If air is blowing out the unloader valve when the air compressor has stopped, then it is most often a failed tank check valve that is the cause of this.
Air blowing out of the PRV at a lower pressure than the normal cut-off pressure of the compressor typically means the PRV has failed and needs replacement.
If the PRV is OK, then as to your new pressure switch, I suspect either the switch is installed incorrectly and isn’t cutting power when it should, or it has a too high cut-out pressure setting, or it has failed.
There isn’t enough information about the pressures in the tank when the problem occurs to be specific.
Thank you for posting my dilemma.
Well, it turns out that after replacing the pressure switch, the check valve, & the unloader valve, I found that the PRV was bad. (Actually, all of the parts needed replacing.) So, I found a place that carries that part, spent another $12.00, and wah-lah! Success!
I forgot to mention that the tank max pressure is rated at 175 psi. If you looked at the picture, you’ll see two gauges. The gauge on the left (the “out” pressure) was set too high. I adjusted it down to about 75 psi. I turned it on, and it ran like a champ, shutting off by itself like it’s supposed to.
Hopefully, this posting can save someone the trouble of having to figure out the solution to the same problem I was having.
Harbor Freight Compressor Will Not Shut Off? Why Does My Compressor Keep Running?
I have a central pneumatic oil-less compressor (3gal oil-less) compressor that builds to 40PS but won’t shut off also at what psi is it supposed to shut off?
If yours is the “3 gal. 1/3 HP 100 PSI Oilless Pancake Air Compressor ” then the normal cut-out will be 100 PSI.
Not knowing the model of the compressor makes this a bit more complicated.
Howe about looking on the troubleshooting page and reading the pages about HF compressors, and other brands, that don’t build pressure?
When you’ve done that, pop back here with a comment about what model you’ve got and what you found when you did the checks.
Harbor Freight 21 Gallon Compressor Runs Constantly
I have a harbor freight 21-gallon compressor and I accidentally popped off the pressure switch.
I thought I got it back together correctly but now the compressor lever to turn it from AUTO to OFF does nothing and the compressor runs no matter what the lever is on.
The pressure switch brand is Lefoo.
Lefoo is a common brand of pressure switches.
If, as I understand it, you somehow disassembled the pressure switch and you cannot reassemble it (no shame there, I couldn’t either), you can get an exact replacement for many places online.
When the compressor is running, does the tank pressure continue to rise to the point that the PRV releases? That being the case, get the pressure switch changed sooner rather than later, as your air compressor is in a dangerous configuration.
Yes, you are correct. I accidentally disassembled it and apparently, I didn’t get it back together right. I let it run until about 140psi then shut it off because it is supposed to shut off at 125psi. Thanks for the help.
You are welcome. For safety’s sake, get a new switch on the compressor sooner rather than later, will you?
Or, if you want a challenge, check out the page on putting a switchback together linked from the troubleshooting page on this site.
Kobalt 8 Gallon Compressor Won’t Power Off?
Kobalt 8-gallon compressor won’t power off when it reaches 150 psi.
When the tank pressure reaches 150 psi, the unit is supposed to power off. It does not.
Instead, the pressure release valve releases the pressure, and the unit stays on. This happens over and over.
I replaced the pressure switch, but nothing changed.
Try removing one and then the other wire from the pressure switch. Make sure the wire can’t touch anything. Plug it in, and turn it “on”. Does it run?
Please let us know.
My compressor does the exact same thing. I replaced the switch and same problem. I unplugged one of the wires, and yes it powers off.
Please let me know ASAP. Thank you.
If you’ve already replaced the pressure switch, and it still doesn’t turn off, then either they are sending the wrong part, or the PRV is bad and letting go too soon, before the tank pressure reaches the proper cut-out setting.
Are there markings on the switch? Is the pressure actually going over 150, like 160 or so, before the PRV lets go?
If the pressure is going high, then all I can tell you is to complain to the part source. What you are getting is either the wrong part or a defective one.
Porter Cable C2002 Compressor Will Not Shut Off – Why Does My Air Compressor Keep Running?
I have a C2002 porter cable compressor that continues running, I have replaced the check valve, installed a regulator kit, and replaced the pressure switch.
If I set the regulator at 80lbs it continues to run past 120 lbs never to shut off.
I always have pressure and it will hold its pressure forever.
When I use it I shut the compressor on and off manually.
Does it run until it blows off the PRV Jim?
You asked me if the PRV blows off. No, because I haven’t let it run that long for fear that the compressor could blow up and do damage or injury.
if you pull on the PRV and air comes out, and you push it back in to stop the airflow, it’s a pretty good bet that the PRV will open itself and dump air when the pressure gets to its cracking point. That’s its purpose.
When you say “If I set the regulator at 80lbs it continues to run past 120 lbs never to shut off.” the air regulator has no control over the On/Off of the compressor motor. It’s the pressure switch that does that.
If your air compressor runs and the tank pressure bypasses the cut-out setting of the pressure switch, it’s typically a pressure switch failure or improper wiring that’s causing that.
You say you’ve replaced the pressure switch. If it was working, when the tank pressure reached the cut-out setting, the switch should trip off. If it’s not the switch itself is likely the problem as long as the tank air pressure reaches and bypasses the pressure switch cut-out setting. What is that for your switch, Jim?
If you have any questions regarding air compressors not shutting off, please leave a comment below, with a photo if applicable, so that someone can help you!