Compressor Pressure Switch Is Leaking Air

What has happened to it when your air compressor pressure switch is leaking air?

Essentially, there are two reasons why this can occur.

But first, lets talk about what the pressure switch does for the air compressor.

A pressure switch reacts to pressure. In the case of your air compressor, the pressure switch is typically plumbed so that the air from the compressor air tank can flow to the switch. It is the air in the compressor tank that the pressure switch is sensing.

General Air air compressor pressure switch

Compressed air pressure pushes equally in all directions at the same time. So, if the tank gauge reads 120 PSI, then there is 120 lbs of force pushing on each square in of tank area, and through the line up to the pressure switch, 120 lbs. of force is pushing on each square inch of the diaphragm inside the pressure switch.

It is the tank pressure pushing on the diaphragm inside the pressure switch that causes the pressure switch to trip.

Why a compressor pressure switch is leaking air – reason one

Reason one why your compressor pressure switch is leaking air is that, over time, the diaphragm inside the switch has cracked or worn a hole, and air is blowing from inside the tank, through the hole in the diaphragm, and existing the switch housing through any convenient opening.

In the photo above, the electric wire ports would be logical places for air to exit the cover should the pressure switch diaphragm have become holed. If the wire strain-relief fittings fill the apertures in the switch, then it may be necessary to pull the cover off the switch to investigate for leaks. If you do this, ensure that the compressor has been unplugged from any power source.

In this photo, note also that the unloader valve for this pressure switch is located on the outside of the switch. If air is exiting the pressure switch cover, then it is almost certain that the diaphragm has failed. That may not necessarily be the case if the


If, when the air compressor has reached cutout pressure and stopped, you notice that air is blowing out any openings in the pressure switch cover, or if you remove the cover and feel air escaping, and particularly if the unloader valve is plumbed outside of the switch, then you either disassemble the switch and replace the diaphragm, or you replace the switch with one of the same pressure and voltage rating as the old model.

Getting parts for pressure switches may be difficult. Disassembling them and reassembling them is, too, quite complex, particularly when you may only do it once or twice in a lifetime.

If it were us, we’d simply purchase a new switch and replace the old. In this manner the removal and re-installation is straightforward, you get a new diaphragm in the switch, and you also get new points, which are another wear item in a typical compressor pressure switch.

Why a compressor pressure switch is leaking air – reason two

If you notice that the pressure switch on your compressor is leaking air, locate the unloader valve, and try to determine if  the air is leaking from the unloader valve or from the switch itself.

If air is leaking from the unloader valve when the air compressor is stopped, that points to a problem with the compressor tank check valve not seating properly, or its failure.


If the air is leaking from the unloader valve, then see the page under Fixing Compressor Problems about air continuously leaking from the unloader valve for more information.



  1. I have a 60 gallon air compressor belt drive,here is what it’s doing.. no start,new start capactor,new run capactor.. windings ok..voltage at motor,and switch… Has no ark when switch engaged…is the diaphragm bad in switch?

    • “Motor at voltage and switch” So, you’ve used a meter and see that power gets to the pressure switch, and with the tank empty, power is flowing across the pressure switch to the motor side, Thomas? “Has no arc when switch engaged” means what? You’ve watched the points connect inside the pressure switch, and you cannot see a spark? Doesn’t mean that the connection isn’t working. If, when the tank is empty, you’ve got power on the motor side, then the switch would appear to work. What makes you suspect that the diaphragm is bad then? What’s the make and model of the compressor?

  2. Chris Selander says:

    I have an older craftsman air compressor which is a 5 1/2 horsepower 26 gallon tank and the presume switch has gone bad. Can you steer me in a direction for a replacement part, the numbers are all worn off so I don’t have any model numbers. Thank you

    • I presume you mean the pressure switch, Chris? If so, please take a photo of the existing switch and post in here. Since you don’t have a compressor model number, there is no way I can be certain what switch you have without seeing it.

  3. Thanks for the Good article.

    I have a electric air compressor that wasn’t used for about 7 years, and when I got it, it leaked. So I took all the connections off on the entire machine. I cleaned them with a wire brush and put them back together with pipe tape. And it began to leak even faster to the tune of a 5 gallon tank gone in about 2 hours.

    You may be on to something here. Question, whats the best method for spotting an air leak? and 2nd what’s the best place to buy these parts such as a pressure switch?


    • Your first culprit may be the tank check valve, Victor. So do check that and make sure that it doesn’t leak. As to parts for your compressor, if you Google your compressor make and model number, you may find sources. We appreciate your kind words.

  4. I replaced the pressure switch on my air compressor and the new switch leaked. I return that switch and got another new one and this one is leaking too. I know it is not the unloading valve due to it is not located at the switch. Do you have any suggestions. could two new switch be bad?

    • Different pressure switches have different unloader valve configurations. If your new switch has an internal unloader valve, and air is bleeding out of the switch even when the compressor is off, that points to a leaking check valve for us, not a problem with the pressure switch. When you say that “I know it is not the unloading valve due to it is not located at the switch”, if the leak is not at the pressure switch, why are you changing it? We’re obviously missing something here. Maybe you could add a comment here with more details, and, if you want, upload a photo of where the compressor is leaking, along with what is it’s make and model number?

      • It is leaking at the pressure switch and this is the second new switch I have tried. Attached it a picture of where the new switch is leaking. It is an old Craftsman 6hp 60 gallon single stage.

        • Hey Louis. If the pressure switch is leaking, and it’s the second pressure switch you’ve tried on your old Craftsman air compressor, then it’s not likely the switch that’s the problem. Our suggestion is that you want to have a look at your tank check valve, and if you see that page on this site, you’ll have a better understanding how the tank check valve, and your pressure switch unloader valve work together. Simply put, we’d bet you’ve got a leaky tank check valve. Hope this helps, the boys at

          • Thank you for you help I will try that this weekend and let you know how it goes.

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