air compressor faulty

ritchiehulse · Jan 22, 2012

hi just wondering if anyone can help me

i have a air compressor, the type used for spray guns, air tools etc that is no longer working.

I opened the case as I could smell burning and found the capacitor was all melted and blown, it was a 25mf so I changed that and the compressor fired up again worked for about ten minutes then stopped again.

If i now turn it on with the new capacitor it will do nothing but hum unless i spin the fan on the motor myself then it will spin but very slowly, if i disconnect the new capacitor it will continue to make the same noise. If i was to put the old cap back on the motor will spin but very slowly.

It is a single phase 230v compressor

I have tried to test the new capacitor to see if it is working correct but please correct me if i have tested it incorrectly, i only have a megger multi meter with digital display and not the bar.
I put the the capacitor on voltage test which was 0v this indicates short circuit, I then turned to ohms where i would hear the click to indicate continuity but would not get a reading, turn back to voltage test where i would get 4v and would slowly discharge until the reading was back to 0v

any help would be very much appreciated, thanks richi

Marvo · Jan 23, 2012

The first thing I would do is fit another replacement cap and check the start and run current of the motor using an ammeter and the on-line votage using your favorite voltmeter. Compare the results with the currents/voltage stamped on the motor info plate.

There could be lots of reasons a motor capacitor would prematurely fail. They would include;

Low supply voltage
High supply voltage
Air dump valve failure causing starting under head pressure
Poor wiring termination causing arcing
Pressure switch faulty causing contactor chatter
General motor short cycling for whatever reason
Belts overtightened
Bearing lubrication failure and overheating
Compressor head assembly mechanical problems.

I haven't had time to check out your exact model so some of these might not be applicable.Bottom line is this is the kind of problem that will only be found by getting hands on with a tester whilst the machine is running. There are mechanical and electrical hazards involved, even when the power is off (especially with capacitors), if you're not comfortable with working on live machinery I would suggest you get a service technician in to help. .