Air compressor problem

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I have a 60gallon kobalt aircompressor oil type. Not many hours on it. The problem is it runs fine until it gets to say 65psi , then the motor slows and lugs, at times it almost slips the belt. I let it cool down to see if it was heat related. Completely cold with 65psi in the tank, it immediately lugs when turned on. It previously pumped to about 150-155psi.

Ideas? Has proper oil level.
 
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Can you hook an amp meter up to the power line to see what the motor is drawing? Since this is belt drive can you turn the power off then remove the belt and spin the flywheel by hand once it gets to 65psi or when it starts to slow? With an almost slipping belt, it seems like the pump is acting up causing the motor to really work drawing a lot of amps or maybe even tripping a breaker.
 
Originally Posted By: chemman
Have you tried changing the oil in case it had become too thick?


After break-in i changed it with amsoil synthetic compressor oil. It really has seen little use since then , maybe 10 or 12 fills.
 
I'd suspect that one of the valves is sticking closed (broken valve spring or valve mechanism), and the poor compressor is pumping against a block. I'd call Kobalt and get their input before doing any dissembling.
 
It is usually the valve. Sometimes, squirting some lubricant on it can help.

You just have to figure out where is the valve.
 
When the run capacitor went bad on my 5 horse, it ran really rough with no power, and started kicking the circuit breaker.
 
Does it have trouble starting, or is it having trouble running? Trouble starting if the tank is pressurized could be your unloader valve is not working. Trouble running sounds like a bad motor capacitor.
 
As stated, run capacitor if it has one. There may be two capacitor bulges on the case, or it may have a separate run capacitor.
If it has a 2 stage compressor, and the second stage valve fails, then the big first stage cylinder does all the work, and this will bog the motor.
Valve in head stuck on compressor.
Loose belt may lead you to wrong conclusion, that there is something more wrong.
 
You may be able to find a local guy who does electrical motors if you can't figure it out yourself. I use a local guy to rebuild window motors, alternators, etc.
 
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It starts and runs fine, normal until it hits 65psi, then it lugs and slips the belt so i don't think its the capacitor/motor. Its something in the compressor.
 
The more expensive HF DVM can test capacitance and I found it handy when testing a capacitor in my generator.

You can also use an ohm meter and watch the ohm meter charge the capacitator.
 
Originally Posted By: spasm3
It starts and runs fine, normal until it hits 65psi, then it lugs and slips the belt so i don't think its the capacitor/motor. Its something in the compressor.


Sticky valves in the head. Sometimes the result of running the wrong oil, but Kobalt's are known of valve problems- I bought mine used, it was rebuilt for that issue.
 
Originally Posted By: HangFire
Originally Posted By: spasm3
It starts and runs fine, normal until it hits 65psi, then it lugs and slips the belt so i don't think its the capacitor/motor. Its something in the compressor.


Sticky valves in the head. Sometimes the result of running the wrong oil, but Kobalt's are known of valve problems- I bought mine used, it was rebuilt for that issue.


Good to know. I have one of their compressors, is there anything to do to prevent sticking valves? I have RP synthetic compressor oil in it, and no problems at the moment. Thanks...
 
It's the 2 cylinder side-by-side that had the problems, many are getting on a decade old, rebuilding them with OEM parts seems to fix it just fine, they improved the parts quality some it seems.

This is just my opinion based on a.) my compressor's history and b.) reading every thread available on Kobalt 60 gallon compressors.
 
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