If your  compressor runs but never reaches stopping pressure that means it will never stop. That is, the compressor won’t stop until the motor gets hot enough because it never shuts down to either activate the thermal cut out and shut down, or actually burns itself out.

The why of a compressor that runs and never stops running is covered on a number of pages on this site, yet it appears as though the information isn’t being reached. Here are the top 4 reasons a compressor will run but never reach stopping pressure.

Porter Cable C2002 oil free air compressor
Porter Cable C2002 oil free air compressor

I’ll try to clarify further and hopes this helps. Here are the typical reasons a compressor will run and run but never reach the stopping pressure.

Compressor runs but never reaches stopping pressure – reason 1:

There is an air outlet on the air compressor that is open, or leaking, and air escaping from the compressor has reached the point where it is bleeding off at about the same speed that the pump is putting air into the tank.

Not all air leaks occur immediately. It is possible that the air leak starts when the tank pressure reaches a certain pressure level and the back pressure from the filling tank makes the compressor work harder, and that along with the higher pressure forces the leak open.

Make sure there are no leaks. Use a liquid dish soap to water solution (1 part soap – 10 parts water) brushed on all fittings, unloader valve, and tank drain to try to located and then rectify any leaks.

Some companies offer leak detection equipment that will react to the sound of air leaking to register on the device. While suitable for larger plants, this typically isn’t practical for a small compressor, unless you know someone who knows someone and that person can borrow the detector your your use.

Compressor runs but never reaches stopping pressure – reason 2:

The compressor operator is using an extension cord that is under-rated for the motor draw or the length of the cord for that load.

This simply means that if – for example – your compressor had a gasoline engine instead of an electric motor, and it needed 1 gallon of fuel an hour to run under load, and the fuel line became clogged and only 1/2 gallon per hour of fuel was getting through, the motor would still likely run, but it couldn’t run fast enough to keep up with the load as it increased due to air consumption or back pressure from the tank.

Yes, I know gasoline driven compressors have a different control system than do electrically driven compressors, but the point I’m trying to make is if your “fuel line”, the extension cord is too small for the motor’s draw, then the motor will run, but will not be able to build enough force to drive air into the tank past a certain pressure, the motor will be damaged and will certainly overheat.

What Size Extension Cord For An Air Compressor.html
What Size Extension Cord For An Air Compressor.html

The take away for this section is, if you are using an extension cord to power your compressor and are having the issue of “Compressor runs but never reaches stopping pressure” then try plugging it directly into a wall socket and see if that makes any difference. That will help determine if it is a power supply issue causing this compressor problem.

Compressor runs but never reaches stopping pressure – reason 3:

Compressor motors often have capacitors mounted on or near them. These are devices (sometimes 1 – sometimes 2 – sometimes none) that help the compressor get started and to run more efficiently by providing an electrical boost to the motor.

If the capacitor(s) is failing, that may result in insufficient energy for the compressor motor to overcome increasing pressure from the tank as it fills, and that can lead to a motor running too long and overheating.

The way to determine if a compressor motor capacitor is at issue is to test it, and here is how.

Compressor runs but never reaches stopping pressure – reason 4:

Well now, if we’ve reached this point and the compressor still has the stopping problem, that usually means that there is a problem with the compressor pump itself.

These problems include:

  • an intake or pressure valve is cracked or broken
  • the gasket in the pump head that separates the low pressure from the high breaches at a pressure level and air just circulates back and forth and not into the tank
  • The cylinder barrel is scored allowing air to bypass the piston
  • The piston seals are worn allow air to bypass the piston
  • A remote possibility that the tank check valve is compromised at a certain pressure stopping further air from getting into the tank.

Except for the last of these, a pump tear down and inspection / repair is the next step.

If it is the tank check valve, with the tank empty and compressor off, removing it and checking it / cleaning it / replacing it are your options.

The above are the typical reasons a compressor will run until the tank pressure reaches a certain level and then stops rising, and the compressor runs on an on. If tackling these doesn’t solve this issue with your compressor, please add a comment along with a photo of the compressor, including make and model.

Good luck.