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.