Air compressor motor quit

[Cadillac STS]

I have a 20 gallon air compressor bought new but I have had it for years. It has always been reliable.

Today I went to start it but the motor didn’t turn and it dimmed the lights in the shop like there was a short so I turned it off quick. I did leave it longer one time and it tripped a breaker.

I removed the cover and took the belt off the motor. Like that the motor runs fine and would start several times no problem.

The pump pulley moves freely and I can turn it easily by hand and could feel the compression.

I put the belt back on and turned on the motor but this time gave the pulley a good pull to help the motor. It ran like that. But after that it did not start on its own again.

What is the problem? Does the motor need to be replaced?

 

[Truckmannorth]

Sounds to me like the start Capacitor or the start switch in the motor. Should be an easy fix.

 

[cathead]

A lot of compressors have an unloader valve. If that malfunctions, the motor will struggle to get up to speed
and draw a lot of current in the process.


I just reread the post and I see the motor wouldn't start with no load my itself so I have to agree with mkjs
on the failing electrolytic capacitor.

 

[mksj]

Most likely start capacitor, typically it may just hum and if you spin the shaft will start or might turn with no load because the capacitor is not completely blown. Easy and relatively inexpensive replacement capacitor would be my first suggestion. You may want to get a capacitor with a higher voltage rating, often AC types are a bit more robust. The start capacitor is an electrolytic, they have a finite life span and frequent start stops or a faulty centrifugal switch will result in their quick failure.

 

[Cadillac STS]

I’ll pull the capacitor and change it out.

 

[matthewsx]

I’ll pull the capacitor and change it out.

Standard repair, let us know how it works out.

John

 

[Cadillac STS]

I am a big proponent of follow ups. For now and forever with people searching for help

It was just corrosion!

I opened it up to replace after ordering the part and one terminal was corroded off. It was in half when I pulled it off.

I cleaned it out and crimped on a new terminal and it worked as before!

Is that a signal the capacitor is going bad? I plan to use it until happens again.

 

[Janderso]

A lot of compressors have an unloader valve

This fixed my similar problem.

 

[Janderso]

Is that a signal the capacitor is going bad? I plan to use it until happens again.

I would just jump and buy a new one. I always appreciate you frugal guys. I wish I was more like you.

 

[pontiac428]

The cap is leaking electrolyte that has attacked the copper parts. Mallory makes good stuff. Probably just time to replace them.