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When an air compressor will not stop it could signal a problem with how the air compressor is pumping air into the compressor air tank.
Or, when an air compressor will not stop, it could also signal a major safety concern, and should be addressed immediately, before using the compressor again.
Compressor pumps up past cut out
If an air compressor runs, pumps air into the air tank, the tank pressure reaches the normal cut out pressure setting level, and the compressor continues to run and the pressure continues to build, this is a real problem! Eventually the PRV will let go, and the tank pressure should vent. The compressor will still run at this point though, and if it isn’t being monitored, it could run itself to death.
PRV doesn’t let go
The safety backup for the air compressor pressure switch is the PRV, the pressure relief valve.
The air compressor can pump air pressure into the tank to a level higher than the compressor is supposed to. If that pressure gets too high, there could be a major failure of a part, and if that compressor part is the tank, well, the results wouldn’t be good.
The PRV is factory set to a pressure higher than the cut out pressure of the pressure switch. If the pressure switch does not shut the compressor down at the normal cut out pressure setting, when the tank pressure reaches the PRV set point, the PRV opens and vents the air. If the PRV fails, my friend, you have a real serious problem!
If the compressor pumps air pressure past the normal cut out pressure setting, my advice is to not use the compressor until this is fixed.
Your compressor pressure switch should shut the compressor off
A typical pressure switch on your air compressor might be the Condor brand, similar to the one in the photo.
It is the compressor pressure switch that is supposed to shut the air compressor off when the tank pressure reaches the cut out pressure level. That pressure cut out level may be in the 100 PSI through to 175 PSI level, depending on the brand and size of your air compressor.
The pressure switch reacts to the pressure in the tank and when that tank pressure reaches the cut out pressure setting the pressure switch trips to off, the power to the motor is cut, and the compressor stops. That is, if the pressure switch is working.
If the compressor continues to run past the cut out pressure setting then it is a pretty good bet that the pressure switch has failed. As far as I’m concerned, it is time for you to get a new compressor switch.
Replace the pressure switch
I know that finding after market parts for air compressors is hard, as so few of the stores that sell air compressors stock a comprehensive list of spares for the dozens of brands that they sell, and have sold, over the years.
When you are looking for a replacement pressure switch, as long as the replacement switch fits the mounting on your air compressor, if it connects properly to the existing unloader valve – or has an internal unloader valve – is the same voltage range as the existing and has the same cut in cut out pressure settings (or is adjustable) then you can use it.
It is not necessary to replace a pressure switch with exactly the same make and model. That is, unless your air compressor is under warranty. Using an off-brand part may void the warranty. But on the other hand, if the air compressor is under warranty, see the store where you bought it and give them the problem of replacing the switch. 🙂
That should take care of the case when an air compressor builds air pressure up past the cut out, and the compressor runs until the PRV lets go.
Air compressor will not stop – still
OK, there is another scenario where the air compressor will not stop and just keeps on running.
That is when the air compressor tank pressure will only pump up to a level that is below the pressure switch cut out setting.
That is to say, your air compressor starts OK – probably from an empty tank when you go to reuse it again, but instead of pumping up to the 100 – 175 PSI expected, the pressure in the tank only gets to 20 PSI, or 30 PSI or 80 PSI and levels out there. Even though the air compressor continues to run, the tank pressure refuses to increase.
Not correcting this problem can lead to self-destruction, or at the very least, overheating of your air compressor.
There are a number of reasons why this happens.
Failures on an air compressor that could cause this include:
- intake valve failing
- pressure valve failing
- blown gasket inside pump
- tank check valve is impeding flow
- compressor leaks somewhere at the same rate that air is pumping into the tank
… to name just a few.
All of these will be discussed as a separate page linked under the Fixing Compressor Problems link.
More pages on this subject include: