Air Compressor
       Blowing Circuit

The Question: Air compressor blowing circuit

"My air compressor will, at start, do fine. After use, when it tries to re-start the motor to refill the tank it breaks the circuit on start up?"

Here is what I think is happening when an air compressor is blowing the circuit on startup.

When your compressor tank pressure drops to the cut in pressure level, your pressure switch trips to allow power to flow through it and that power tries to start the motor. If the compressor motor is successfully started the compressor pump generates more air, the tank fills, the high pressure cut out is reached, and the pressure switch cuts the power to the motor. The compressor stops compressing air.

In your case, when the compressor pressure drops, the pressure switch tries to turn on your compressor motor, then your circuit breaker, or your fuse, blows.

circuit breaker and fuse panels

The problem could be a poor power supply to the compressor, a failed pressure switch, a motor capacitor failing, the compressor motor itself, or the unloader valve may not be working.

All of these issues, individually or working together, can create a scenario where your air compressor tries to start and in so doing it blows the circuit breaker.

Steps To Correct Air Compressor Blowing Circuit

Drain the compressor tank to zero PSI. Try to start the compressor. If the compressor starts OK monitor the operation carefully, particularly when the tank pressure is approaching the cut out pressure setting. Make sure that when the compressor reaches cut out, that the unloader valve works as it should.

A failure of the unloader valve will trap air over the compressor piston when the compressor stops. Then, on restart, the compressor motor has to struggle against the increased load caused by that locked in air pressure.

When this happens a typical result is that the motor pulls more amps when trying to start against this trapped-air load. The motor draw quickly exceeds the capacity of the circuit, and pops the circuit breaker or burns a fuse.

Please have a look at the Unloader Valve page linked from the site map page if you need more information on the unloader valve and how it works.

As noted there are a number of other reasons why an air compressor is blowing electrical circuits. By eliminating this one common cause you will help narrow the field subantially and likely solve your compressor problem.

Other causes and resolutions for when an air compressor is blowing circuits are covered on the pages of this site. Or, if you have a question, visit the forum linked below.