Does My Compressor Need A New Pressure Switch

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.

Inside the pressure switch - fix-my-compressor.comIf 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.

Pressure switch for a small compressor - fix-my-compressor.comOr, 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.

 

Comments

  1. 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?

  2. Jeff Whitworth says:

    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.

  3. 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.

  4. 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!

  5. 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.

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