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Posted on Mar 22, 2009
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Air compressor fills, but slows down as the pressure builds

After i changed starting capacitor air compressor begins to fill runs good for couple of times.and now air starting fills with air, but slows down as the pressure builds up in the tank about 60psi. It is an oil lubricated twin cylinder. The motor is a Doerr Emerson Electric 15 amp. I tried replaced running capacitor but same result.
what is problem?

  • Anonymous Mar 23, 2014

    Compressor lubricant

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1 Answer

Joe Garcia

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  • Posted on Mar 23, 2009
Joe Garcia
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Sounds like you need a new check valve which should be somewhere between the compressor outlet piping,tubing,etc and the tank which prevents the air in tank to back feed to the compressor which would cause hard starting and could damage the motor easy way to check is when you shut off the compressor with some air in the tank if the check valve is bad it would continue to bleed air out out the unloader valve .the unloader valve on your unit is most likely part of the pressure switch when the unit shuts of it should only bleed down the pressure in the pump so it would make it easy to start when needed hope i didn't confuse you

  • rezero101 Nov 03, 2010

    I bought the 60 gallon compressor brand new at Lowes. 2 months in the set screw for the big pulley fell out and started rattleing around. 6 months in the belt started to burn and stink. 6 months after that the compressor slows down tremendously at 60 psi and takes forever to build up enough pressure that by the way is now around 142psi opposed to 135psi which is where it use to stop. in the last several days i have changed both capacitors and the check vavle. had a certified person come and take a look and he says the cylinders look brand new and all gaskets are great. his only advice is a new motor. The motor is only a year old. obviously i am not happy with Campbell Hausfield and would never reccomend it to anyone unless i can get some excellent customer support

  • markusunread Dec 04, 2010

    The check-valve tip is great - but there is another failure that can cause the same symptoms. If your compressor motor has a "run capacitor" along with it's "start capacitor", it can be a bad "run capacitor. I have a compressor like that, with two "lumps" on the motor. One is the start capacitor and the other the run capacitor. The run capacitor failed shorted and the motor would struggle for a few seconds until it popped the breaker. To check the capacitors, disconnect them from the motor, short the terminals and use an ohm-meter to check for a short. If the resistance starts low and goes up, the capacitor is good. If the resistance stays the same and low (less than 100 ohms) it's shorted. If the capacitor, after shorting the terminals, immediately shows a very high resistance ( greater than 1 megohm) then it has probably failed "open".
    I found an unexpected source for motor run capacitors - pool/spa parts suppliers!

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