Air compressor not shutting off [Relocated thread]

This is a little off topic. I have an old Montgomery Wards air compressor. A little 20 gallon on wheels 110 volt motor. I just had to replace the regulator due to cracking in the threads. Now, after replacing the regulator, the auto shut off does not work. Regulator is set to 120 psi same as it was before. It used to shut down @120 and kick on again @90. Now when it hits 120, it just keeps going & going & going. I have to manually shut it off.

 

It could be the points in the regulator are sticking, or the plunger that pushes them open is stuck. It can also be the 120 on the regulator isn't matching the 120 in the tank and the compressor can't build enough pressure to kick the regulator off.

You might try setting the regulator lower to about 90 psi and see if it kicks off. If no setting will get you a kickoff, the problem is in the regulator for sure.

 

A regulator is a pressure reducing device to be able to deliver lower pressure than what is in the storage tank and the pressure switch is what turns the motor on and off in response to pressure in the tank.

I assume you replaced the pressure switch.

Did you wire it correctly?
Most pressure switches are two pole and it is easy to get mixed up on the connections.
Also, does the pressure build up beyond 120 psi when it continues to run?

 

Did not replace the switch as that was working just fine. Only replaced the regualtor due to a big crack hed developed.

 

It must be the compressor isn't building enough pressure to kick it off, Indy. Try a lower setting on the kickoff switch.

 

The pressure regulator has no effect on what pressure the switch turns off the compressor.
One thing that could have happened is if you did something with where the pressure switch connects to the tank.
The switch must sense tank pressure at all times and must not be upstream of the check valve and not downstream of the pressure regulator.

You did not say if the pressure continued to build as it kept running.
If you somehow mixed up the connections and are sensing pressures downstream of the pressure regulator it would give the symptoms you have.
Won't shut off 'cause the regulator is not set high enough and the gauge will not be reading the tank pressure 'cause the regulator will also be doing its job.
If this is a possibility you would be relying on the pressure relief to protect you from flying metal.

Something to check out.