Air Compressor trips Breaker

[skipatroller]

Any Ideas?

I borrowed my dad's air compressor and when I plug it in the garage it will try to start and trip the breaker (20A breaker and it seems fine as I can run an number of other things on it without tripping). It sputs and sputters to try to get going, until it trips the breaker. However if I bleed the air off in the tank, it will start up fine and run until it hits the high pressure shut off.

I am thinking that the starting capacitor on the motor is getting weak and this is showing when starting against the pressure in the tank. I would think that the "run" capacitor is fine as it runs fine once it starts. I think I will stop by Grainger's to see if they have a new starter capacitor on the way home.

What are other's thoughts. Am I chasing the wrong thing?

[mdshunk]

While it could be the start cap, I'd rather suspect the more common check valve or unloader valve.

[xkvator]

also check the nipple from tank to pres. sw./unloader. moisture causes them to rust/clog up.

[skipatroller]

Quick update.

I changed the starting Cap. and the thing still spits and sputters and finally trips the breaker. (now I think it is because it is starting against a Load) '

Next step is to tear the check valve out and see if I can see any problems. I tripped the unloader valve (on the side of the pressure switch) with my finger and it seems to let the pressure off.

Thanks for the suggestions.

Bob

[homebild]

How far from the outlet do you have the compressor plugged in?

If it's on an extension cord over 50 feet long you can get these symptoms.

[skipatroller]

It's just the 5-6 foot cord on the compressor itself plugged directly into the outlet (and I tried several outlets).

Thanks for the suggestion though.

Bob

[bcreely]

your problem is the unloader valve if the compressor will start and run with no pressure in the tank. starting under load draws high current that will kick the breaker. when unloaded, the flywheel gets up to speed quickly and keeps everything rolling. i'm guessing your running current is very close to your breaker size.

[ggratecc]

See this link: http://www.epinions.com/content_160758861444

The bottom line is this: Craftsman compressors are known for
bad capacitor centrifugal switches, which trip C/B's.

[skipatroller]

OK the compressor is still tripping the 20 A breaker (actually it will trip any of several breakers - so it is not just a weak breaker)

I cleaned the air intake filters and still had the problem.
I tried changing the starting Capacitor and still had the problem.
I have checked the operation of the unloader and check valves and they seem to be working fine.
I changed the oil in the Compressor pump crankcase to a synthetic oil and I still have the problem.

A little bit more info on the compressor. It is a PUMA brand compressor (model PK-3022, 3 HP, 21 gallon tank, 9.3 cfm) that was bought in 1992. It has a 2 cylinder belt driven compressor pump. The motor has both a Start Capacitor and a Run Capacitor. (like I said I tried changing the start capacitor with no luck). The symptoms seem somewhat temperature related - that is it shows up when the compressor is cold (haven't had any "warm" temperatures in North Idaho the past several months to see if it goes away when it is warm) . Once I get it started (ususally by bleeding all the air in the tank) and it runs enough to get "warmed-up", the compressor will run fine (switching on when the pressure in the tank drops and shutting off at the upper limit), unless it sets for too long with out running and then it will trip the breaker again.

The problem seems to be related to the switching between the "Start Mode" and the "Run Mode" on the motor. The motor starts and trys to switch modes and then it ends up switching back to the start mode. This goes on until it ends up tripping the breaker. While it is doing this "coughing" of trying to get up to speed I can see some arcing if I get down and look in the vents of the motor. "ggratec" posted to a link for a similar sort of problem for a direct drive craftsman compressor. I think I will try to have a look at the motor and see if it has a similar problem.

Like I said the thing seems to run fine once it gets "warmed-up". If it didn't run so good when it was warmed-up I would think about changing the motor that drives the belt.

Any other ideas or suggestions.

Thanks

[ggratecc]

I don't claim to be a compressor expert (mechanical end of it),
however, it still sounds like you need to replace/repair the
capacitor switch. Sounds like the switch is stuck in the "run"
postion.

[skipatroller]

Since the last update, I pulled the "RUN" capacitor and took it to Grainger's -- they tested it and it was fine (measured 31 microfarads vs its rating of 30 uF)

Also pulled the "switch" off the end of the motor and checked it out. Everything seems fine (it doesn't have the problem that ggratec pointed me to -- the disc is tight against a snap-ring on the shaft)

When I try to run the motor, it starts fine. Starts coming up to speed and then trys to 'switch' from start mode to run mode. It is like it isn't running quite fast enough or the 'Run' mode doesn't have quite enough power. At his point the speed drops just enough that it switches back to 'Start' mode, which brings it up to a speed,where it tries again to switch to 'Run' mode. This 'hunting' continues for about 5-10 seconds at which time the breaker trips.

Any suggestions or ideas?

The only thing that I can think of is to pull the motor off and take it to a motor rebuilder to see if they can test it.

Like I said before, If I drain all the air out of the tank it seems to start up and run fine. Once it fills the tank it seems as though it has gotten "warmed-up", and the compressor will run fine (switching on when the pressure in the tank drops and shutting off at the upper limit), unless it sets for too long with out running and then it will start the 'hunting between Start and Run modes and eventually trip the breaker.