# air compressor



## cammack (Mar 20, 2021)

I bought a Schultz 7.5 hp 220 v two stage air compressor with a horizontal 80 gal tank for my son about 3 yrs ago. It ran fine for 31/2 yrs. Then it started to act sluggish when you started it up and sometimes it would trip the breaker. then sometime it starts like it should. Things I have done,. changed out both start capacitors and run capacitor. Kept same mfd and voltage. Check the centrifical switch and it was not binding. Cleaned the contacts on switch. Changed the low pressure valve switch.or unloader switch. Spun the pully and it was not binding at all, spun freely. Compressor cuts in at 135 psi and out at 175 psi like it should. Oil looks ok.I don't see any burned spot on wiring or on terminals. What do you think it is?

John


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## motormonkey (Jul 10, 2016)

See this thread.


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## cammack (Mar 20, 2021)

motormonkey said:


> See this thread.


motormonkey,
Thanks for the reply.
I have already installed a new unloader valve. We have already let air out of tank and started compressor. It builds up air pressure to 175 psi. when using air it reaches 135 psi it comes back on. Sometimes it works ok and other times it doesn't work like it should.. It seems as though it is fighting against air pressure on pistons., sluggish. Sometime it goes ahead and over comes this but other times it trips breaker or reset button. We are thinking maybe we have a loose wire coming from the new unloader. we haven't had a chance to check out where the unloader valve wires go to check the terminals. My next check is the check valve on tank, it might be leaking air from tank to unloader valve.

John cammack


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## iowagold (Jan 22, 2020)

check a couple of things.
they have a one way valve from the compressor to the tank...
it could be leaking internal on the check valve.
to test for this have the tank up to full pressure.
loosen the nut at the head of the compressor output line.
it may hiss for a moment..
but then it should stop and the tank must remain full of compressed air..
if those valves fail they leave full tank pressure when the unload-er is supposed to lower the pressure at that point.
and the compressor is dead headed with high pressure and will not start right. or just lock up.

the second thing is the unloader valve.
that relieves the pressure on the main compressor hard line to the check valve.
you can hear the action when the compressor kicks out with a Hiiiisssssss.
and if that hiss continues for more than one minute... then replace the tank check valve it should be the last fitting before the tank and main compressor feed line...

dirty air or high humidity is hard on the tank check valve they get gummed up... or corrode and erode for leaks.
so make sure the air cleaner assy is over sized and has fine high flow filtration.


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## stevon (Mar 5, 2019)

cammack,

I recommend checking amps on motor with an ammeter at startup and at peak air pressure. I should be within the FLA listed on the compressor. Initial startup amps from 0 rpm will be more because of RLA or "locked rotor amps" for up to a second.

Stephen


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