compressor on the blink

[123hotchef]

Just ordered a new nrv I tried to fix the old one but it didn't want to play. It looked original to be fair

 

[dobbslc]

That rubber bung looks knackered though.

 

[123hotchef]

That rubber bung looks knackered though.

it was actually a hard plastic bung it had a deep indent where it had been sitting thats why it was letting by i thought i could glue a rubber washer on to help seal but nah it didnt work the spring is probably tired too

 

[123hotchef]

this compressor still gives me grief sometimes! sometimes not.
lucky I have hooked up together so when the problem occurs the other unit does the hard work

 

[123hotchef]

Bloody thing is still messing me about. It must be the motor, it builds up pressure to about 80psi then just stalls it keeps trying to start but doesnt. Do I spring for a new motor or scrap the compressor and get a new one.

 

[Hopefuldave]

is it single-phase? If so, try a new run capacitor, they do dry out with age and when they go low-capacitance you don't get as much motor torque - much cheaper than a new motor (a few Local Currency Units) and a lot easier to swap. If it's a two-capacitor motor, change the start cap too!

 

[Dragnet]

The motor sounds fine, as it's running. A motor failure would be bearings (replaceable, and it would be make a horrid noise); windings (smoke, no movement and blown fuses); brushes; centrifugal switch if a two capacitor motor (start capacitor is retained in circuit rather than being switched out once the motor reaches a certain speed, thus wearing out the start capacitor); commutator wear, I guess...

It sounds as though its capacitors are at fault, if it is single phase as Hopefuldave says. Certainly the simplest to swap to check, if you haven't got a capacitor tester. Is there one capacitor or two? If two, can you hear a 'CLICK' as the motor speeds up, and again once it's turned off and slowing down? It's probably a lot more noticeable on slowing down as the background noise is lower. If no click, your centrifugal switch may be welded shut and you'll need to disassemble the motor and file the contacts clean. Or buy a new motor and post the old one to me...

You can get new rubber bungs (they're called 'pastilles') from pneumatic suppliers, which is cheaper than a new NRV. I discovered the NRV on the compressor I've been restoring had bizarrely lost its spring, so that wasn't very helpful. I was able to get a new spring from an air place on a local industrial estate.

Good luck!

 

[123hotchef]

Thanks for the replies and advice. It is a single phase compressor belt driven. I changed the capacitor last year actually there is only 1 cap. That did not make a difference. The nrv has also been changed.

 

[dave h 2]

Bloody thing is still messing me about. It must be the motor, it builds up pressure to about 80psi then just stalls it keeps trying to start but doesnt. Do I spring for a new motor or scrap the compressor and get a new one.

If it can't stagger passed 80psi then it's new motor time especially as the start coil seems to work but the main windings don't take over, not helped by the unloader only working when pressure switch operates.
An AC clamp meter will tell you if it's a bad connection to the coil . A 3hp comp should pull 10 to 12 amps, any lower is a broken wire any higher is a partial short

 

[123hotchef]

Funny thing it has been working fine the last 4 days spraying paint, weird. maybe becuase it is cooler too?