This question is fairly common, in one form or another. Does my compressor need a new pressure switch?
In order to determine this we need to understand what the problem with your air compressor is. Use the comment form at the bottom of the page to ask a question about this, or comment on the content or other posts.
Compressor stops before reaching cut out pressure
If, for example, your air compressor normally cuts out at 120 PSI, and now it shuts off consistently at 95 PSI, that would certainly point to the pressure switch having a problem.
Check the switch by using a multi-meter to determine if, when the air compressor has shut off at 95 PSI, that power is not still passing the pressure switch to the motor circuit.
One side of the switch will be the power supply side, and the other will be the load or motor side. You need to know, when the compressor has cut off, if the power is still flowing from the power supply side to the motor side.
If the power is not flowing, meaning the pressure switch has tripped to off at 95 PSI, and since it’s supposed to trip of at 120 PSI (on our fictional compressor) then the switch has a problem.
What other compressor problems would suggest that it’s the pressure switch at fault?
Compressor Will Not Start At All
In this scenario, your compressor has run up tank pressure to cut out, and the compressor has stopped. Or, you drained down the compressor tank the last time you used the compressor and now that you’ve plugged it back in and switch it on, if yours has an On/Off switch, nothing happens.
The compressor problem may not have anything to do with the pressure switch. However, if the tank pressure has reached the lower cut in setting, or better yet, if the tank is empty, then it is prudent to check the pressure switch.
You do this the same way as outlined above. With the compressor on and the tank pressure well below the normal cut in, use the multi-meter to see if power is crossing the pressure switch.
If you find that power is crossing the pressure switch to the motor circuit, that suggests that the pressure switch has tripped to on, power is moving across the pressure switch terminals to the motor circuit side, and the pressure switch is working properly. It is another issue preventing your compressor from starting, and many of these are covered on other pages on this site.
Compressor goes on and off
You have used air from the tank, the tank pressure has dropped to the normal cut in pressure, your air compressor starts, but then, after filling the tank a bit, the compressor stops for a while, then starts, and repeats the cycle.
In order to determine if this is a compressor pressure switch problem, you will, again, need to check to see if, when the compressor stops building pressure before the tank has reached the normal cut out pressure setting, if the switch has actually turned off and stopped power flow to the motor circuit.
If your multi-meter shows that power is still flowing across the switch and the compressor has still stopped, then it’s not the pressure switch at fault.
If the pressure switch is not passing power to the motor circuit, and the tank pressure is still below cut out, then it is quite likely the pressure switch that’s at fault.
My pressure switch is different
There are dozens of models of smaller air compressors on the market now and many of these have a switch that might look like the following.
Or, yours may be a very small switch than even this one is.
A pressure switch is a pressure switch. In order for them to work, the sensor part of the switch (a diaphragm in the top one – a tube in this one – and a smaller diaphragm in an even smaller switch ) must be acted upon by pressure from the compressor tank. When the cut in pressure is reached the switch trips to passing power, and the motor circuit has power. When the cut out pressure setting is reached, the switch trips to off, and power no longer flows across the switch.
So, regardless of the type of switch you have on your compressor, if power is not passing across the switch when it is supposed to, and you have a good power supply to the compressor pressure switch, then it is most likely that the pressure switch has failed, and it’s time for a new one.
A new pressure switch
We refer to getting a new switch rather than trying to repair them.
Many of the lower cost pressure switches do not have user replaceable parts or, since they are cheap to begin with, there is no incentive on the part of the supplier to stock parts for a low cost device.
Some manufacturers of pressure switches (typically European or North American) have a parts supply network. Yet, if you have never disassembled a pressure switch, it is no easy task. Once the spring(s) let go, getting the switch back together again is an exercise in frustration.
Sometimes the only thing to do is chuck the old one, and get a new pressure switch. Less aggravation, for sure.
Brand new I. R. TS4N5 after 2 months of minimal use pressure switch won’t turn on at low point. I can tap the contactor and then it works and shuts off at the right high point. Unloader works just fine and all electrical is good.
I have a dewalt D55146 4.5 gal 225lb compressor. It is 1 week and 1 yr old. 1 week past the warranty. of course. The problem im having is it will only build pressure from an empty tank to about 6olbs, then it shuts off. Im thinking a bad switch?? motor runs compressor runs, it just wont build to the top pressure. any advice or thoughts?? thank you.
my Dewalt compressor is burning up pressure switches at least once a week in a light manufacturing setting. Measuring 213V going into the pressure switch and 5V out when in manual ON.
My compressor pressure switch wires burned up. Any reason why this would happen all of a sudden.
My guess would be a short in the switch, Mike. That is, of course, that there wasn’t a change in the electrical supply to the switch or a short in the motor windings, though that should have blows a fuse.
My Campbell Hausfeld compressor was working fine, I turned it off, and bled the air out of the tank. After which it would not start. I checked the run capacitors and they were within tolerance but I replaced them anyways due to a crack on one of them. Still doesn’t start. Could my pressure switch have died and needs replacement or would there be another culprit.?
Thank you
Frank, can you check the power, both from the plug to the pressure switch, and from the pressure switch to the cap? Please advise.
i have a 8 gallon mastercraft air compressor with 1.5 motor. ive replace the pressure switch (9828-589316-29) and the pressure relief valves still goes off and the motor never shuts off . ive switched the wires around and it still does it . any help would be appreciated
Dump the air and let it run pressure up again.Please watch the tank gauge. At what pressure does the PRV let go?
130 lbs
If the PRV is letting go at 130 PSI, and this compressor is rated for 135 PSI according to their site, then it’s the PRV that’s failing or is contaminated with something that is allowing it to crack open too soon. Try dumping the air, pulling the PRV, throw it in boiling water or rinse in thinner, let it dry, and put it back on the machine. Let the pressure build to 100 PSI, and manually crack open and close the PRV a few times. Then, let it run up to cut out on it’s own. If the pressure builds to 145 PSI or so, then the PRV may be working OK. I don’t know the normal cracking pressure of that PRV but you shouldn’t worry until the tank pressure gets 15-20 PSI over the normal cut out. If it does, shut it down, drain the air, and get a new PRV.
If the PRV lets go at 130 PSI again, replace it.
If the compressor won’t go past 130 PSI, and the PRV is staying closed, please add a comment here.
I’ve just received a non-working Husky 30-gallon compressor (C303H) – the compressor will not start. The motor and flywheel turn easily and I’ve checked the ON-OFF switch with a multi-meter to be sure it’s working. Am I correct in assuming that if there is essentially no resistance between the terminals of the pressure switch (E108524), that the pressure switch is not the cause of the compressor not starting? If so, then what’s the next most likely thing that is preventing the compressor from starting?
Garry. With the tank empty of air and the plug in the power supply socket, use the multi-meter to follow the power flow. Is it getting to the supply side of the pressure switch? Is the power then getting to the motor side? The pressure switch should have tripped to passing power if the tank is empty. If it is not letting power across the switch, then it’s likely the switch that’s the issue.
Please advise what you found.
The incoming voltage was 115 volts, but the voltage at the pressure switch was only 66 volts.
After disconnecting the power cord, I made several resistance measurements:
I assumed the discrepancy in resistance values between the wiring/brushes and directly through the commutator bars was caused by the brushes NOT being in contact with the commutator. Sure enough – the brushes, which were originally two inches long, only had about 3/8 of an inch of carbon left on them. I also noticed that the commutator seemed to be excessively worn and may not have a consistent diameter (see attached photo).
Obviously, a set of new brushes are needed. The question really is whether or not the $35 investment in new brushes is worth it given the wear on the motor’s commutator. Is the commutator’s excessive wear unusual and is the tremendous amount of carbon dust prevalent over the motor/pump assembly indicative of hard use and further problems?
Certainly long use, perhaps marginal commercial use.
My Husky air compressor is exceeding the max air pressure causing the safety valve to pop off. Could this be the pressure switch?
If the pressure is rising past the normal pressure cut off, and the compressor keeps running until the PRV cracks open, then for sure, it’s the pressure switch that needs replacing. Good luck.
ive just bought a new pressure switch(rated to 175psi). Ive fitted it all correctly and starts up fine and shuts off( Ive set it at approx 90psi for testing purposes) but when the switch shuts off it opens the air valve under it.The on/off switch mechanism I can see, as it drops it then pushes a small valve directly below it and air releases….drops below pressure and compressor starts up again.
Im puzzled as I cannot see anyway of adjusting it.
You don’t adjust that. Ask yourself, when the compressor stops, where is the air that’s leaking out the unloader coming from? What’s supposed to keep the air in the tank? It’s the tank check valve. It sure sounds as though the one on your compressor is leaking.
I have a 2 hp 110 v air compressor that has a few problems. When it achieved pressure -150- it would shut down but the unload-valve would let all the air escape until I released some pressure by pulling the relief valve. Then it wouldn’t start again until the pressure went down to below 15 lbs. It would try but trip the internal circuit breaker. I bought a new valve- Lefoo- it’s exactly the same as the old one, and nothing’s changed. I didn’t change the relief valve.
First step, check the tank check valve, it sounds like it’s leaking. Then if that’s not one of the issues, please let us know.
My switch looks exactly like the photo above. When I was repairing the unit that wouldn’t start at all, I adjusted the torx screw. Tightening it moved the stop pressure higher. Loosening moved the stop lower.
My compressor switch is operated by a red colored plastic lever pushing against a black plastic lever that closes the metal contacts. The black plastic has worn down over the years and wasn’t moving enough with the red lever to close the contacts. I added a few drops of liquid printer resin to the black plastic surface, cured it with a black light, and in a few minutes it had hardened to a smooth surface.
This procedure rebuilt the surface and returned the switch to normal operation.
I have a 6hp 220v and im getting power across the switch and to the motor but my compressor will not turn on? Ive had the motor checked and it works. So would my switch be bad?
If you are getting full power to the motor when the switch trips to on, and power flows, then I doubt it’s the switch. You say the motor was checked. Were the capacitors checked too?
Yes the motor was checked by a professional. I even bought a new pressure switch and my motor still wont start?
I have a Campbell compressor upright compressor 24 volts it does not start I put a I put a new pressure switch and you will not start I need help 206 pressure
You checked to make sure power is flowing through the complete start circuit? That is, from cord, across switch (with tank empty) and to the motor? Is there a start capacitor on that motor? It think we’ve had this conversation before on this site, Jerry. You need to add a comment with details so we can help. Thank you.
Can you please confirm that they checked the current and voltage from power supply to the capacitors, and, did they pull the start capacitor and actually check it?
I am working on an old air compressor with a square d 9013-hhg-12 pressure switch. I’ve had the pressure switch assembly apart and the unloader valve cleaned and working properly. When I turn the air compressor on, the pressure switch kicks out at the set max pressure and triggers the unloader valve until the pressure reaches the kick in pressure and starts the cycle over again. I’m thinking that the pressure switch needs to be replaced.
Any suggestions?
Cody, the pressure switch is normally supposed to open the unloader when it cuts the power. The idea is to let the air over the piston escape before the compressor tries to restart on low pressure.
It certainly sounds as though the tank check valve is leaking, and that’s why the pressure drops as air bleeds out via the unloader that is supposed to do just that. Best check your tank check valve.
I have a 220v 45gal kolbalt it runs fine until it reaches 25psi then runs really slow til it shuts off and i have to push the reset on the electric motor. Would this be the pressure switch?
I don’t think that the pressure switch is on the top of the list here, Joel. If there has NOT been any change in the power supply, and this condition is relatively new, I would suspect that it could be caused by a weakening capacitor. See the page linked from troubleshooting on this site for how to check them, and be careful if you aren’t comfortable working electricity, as 220 V can certainly hurt you very badly.
Which one is the run capacitor? I changed the silver one and it still runs fast and slow to 25 psi until it slows to a stop. Any other suggestions?
Ok so the black one is the start capacitor and it that is fine and I put in a new run capacitor and it ran the same. What else am I missing?
Assuming that there is no mechanical issue binding up the pump (you’ll need to look at the valves in the pump head to be sure), and that the new capacitor has the same rating as the old, then the only other thing it might be is the motor itself.
Having to hit the motor reset to get the motor running again is telling you that the motor is overheating and going off on thermal cut out. Motors overheat due to increasing mechanical load that the motor can no longer overcome, getting insufficient power due to poor power supply or a capacitor not doing it’s job, or the motor itself.
The page about testing capacitors on this site will help that process, rather than just changing them, perhaps? You say which one. I take it you have two. One is a start capacitor, and the other is a run capacitor. Test them both if you would.
My compressor keeps running. Want shutdown. Even pass 120
Hi Steve… if you read the page, it would seem, if you’ve done the checks, that your compressor needs a new pressure switch. However, we can’t be sure as you don’t indicate the make or model, or tell us what you’ve checked yet. Thanks.
I have a 20 gal oil free compressor that pumps up very slow? Slow to achieve max pressor?
Don’t think this is the pressure switch as if it was, the compressor would run or not run, but this wouldn’t have any effect on the slow pressure building. Visit this page for some things to look for.
So my compressor switch (furnace style) has power from wall socket but no power to motor. Verified by multi meter. Will power up if I press the little black tab at the top of the switch but only when and as long as black tab is depressed. Replaced switch with a brand new one. Same results. Did I get a bad switch or is there some other issue going on with my compressor? Checked the fuses and relays already. When wiring motor directly to current, bypassing switch it runs.
Cody, any air in the compressor tank? If so, drain it all, and fire up the compressor again. Your diagnosis of the problem switch was a good one I think. It sounds like the switch was pooched. As to the new switch, sometimes they switch the terminals on different models, so double check to make sure that the power cord wires are both attached to the supply / line side of the terminals, and the motor / load wires are on the their side, will you? Did you for sure replace the ground / earth wire? Please double check all and if they are all right and you have power to the switch, empty tank, no power on the motor / load side then it definitely is the switch that’s the issue, unless… and that’s a big unless, there is a blockage in the line from the tank to the base of the switch and the switch can’t “see” the tank pressure. Please advise.
Thanks. Tank was empty from the get go. I always drain to minimize corrosion, but I did not know that if the tank or cylinder has pressure in/on it then it just won’t fly. Good lesson! Turns out the first switch was a dud. My fiancee ordered the exact same one before I could research them. Was skeptical but just finished installing an IEE Sunny and now my compressor runs like brand new outta the box! Also learned from a few of you pros out there that pipe dope works much, much better than Teflon tape. Thanks again brother, you are a lifesaver!
Good karma sent your way.
Cody
La Grange, Texas
My brute compressor turns on , fills up then shuts off and wont come back on
Well it might be a new pressure switch is called for IF the present switch has an unloader valve as part of the assembly, and that unloader valve is not emptying air over the piston when the compressor stops. Any other symptoms?
My air compressor ran before but had leaks at the old pressure switch. I installed a new, LEFOO LF10-1H, and my air compressor wont start. The air pressure is zero, the pressure switch is on and I read 120 volts where the line in connects but I read zero volts for the motor circuit. The power does not cross the switch to the motor. Do i have a bad switch or am I overlooking something?
Thanks
If the air pressure in the tank is below the normal cut in pressure of the switch, the switch should trip to ON, which means it’s passing power across the switch to the motor circuit. If it is not doing that, either the wiring of the switch is suspect, or, as you point out, it could be a bad switch.
My Porter Cable 2002 compressor runs and pumps pressure into tank but doesn’t shut off and the tank pressure gauge does’t read any pressure in the tank. But when I pull the pressure relief valve I have an abundance of air pressure in the tank There is no air pressure coming out of the tool hose side. Thanks for your help.
The problem with pulling the PRV as a pressure check is that it does not take much pressure in the tank to sound like a lot of air pressure when it escapes the PRV. Consider swapping the two gauges to eliminate a broken gauge as the problem. While a regulator gauge can read zero PSI if there is air pressure in the tank, the tank gauge should reliably show the tank pressure, regardless of the regulator setting. Please let me know as a comment here what you found when you swapped the gauges.
I own a 20gal mastercraft (Canadian tire) with a lefoo lf10-4h pressure switch. Compressor motor turns the pump slowly as if something is restricting it, motor turns slowly, but humms, eventually blows the breaker. If I remove the intake line from the switch, motor runs smoothly, and pump produces air. Help please!
OK Dug, that sounds a bit like there is a power problem. Have a look at this page for some things to check: http://fix-my-compressor.com/air-compressor-just-hums/ .
Have a Kobalt 5 gallon compressor. Doesn’t shut off. Runs until It blows fuse. Pressure build past 120 lb shut off& then blows air out of what I am assuming a safety valve.
Well Jim, that sure sounds like the pressure switch has failed. Once the tank pressure reaches cut out, the power to the motor should stop. If the power continues to flow through the switch, and the tank pressure is higher than the normal cut out, I`d be replacing the pressure switch.
Yeah I actually figured it out. Came back here to post findings….. Check valve…. Once I started really investigating it and a bit more research and understanding (YouTube 😉) the light bulb came on… The check valve. Stripped it down and had a look… The seal in it wasn’t sitting correctly… Why.. Don’t really know buts working spot on now and I know for in future now too