My Rolair JC10 air compressor reaches the set pressure and goes into standby mode with no problems, but when in standby, the motor is humming instead of being powered off. When the tank pressure drops, the motor will resume running, but when it returns to standby the motor hums. Any ideas on how to troubleshoot and resolve this problem?
Air Compressor Problem: Motor Hums in Standby
- Thread starter kc27
- Start date
BillK
Well-known member
Are you absolutely sure it is the motor "humming" ???? The next time it does it unplug it and see if the noise stops.
Hum does stop when the compressor is unplugged. It seems like the sound comes from the motor, I will take a closer look.
The pressure switch powers off the compressor when the set pressure it reached. Are you saying check to see if it is the source of the hum?
If by "coil" you mean the black piece attached to the side of the compressor with the tube coming out of it, that is the air intake filter.
If the switch. Has fully OPENed (motor is off) then there should be no power getting to the motor. If the contacts are sticking the motor could be get some power, or the contacts could be the hum
No, I mean the coil:
micromind
Well-known member
If the coil is a seloniod valve, most likely to unload the head, and it is energized while stopped. They certainly can hum a bit.
My guess is the solenoid unloader valve is humming, not the motor. open up the pressure switch and disconnect the wires to the solenoid . plug it in & see if the hum is gone.
Thanks, I will try that.
The part PCustoms asked about is the solenoid valve. Excerpt from the owner's manual below:
SOLENOID VALVE Your JC10 air compressor is equipped with an electronic solenoid valve which dumps head pressure when your machine reaches top pressure or is unplugged. This type of unloading system provides a load-less restart when the motor overload trips or even if your machine is unplugged while still building tank pressure.
Since I may need one, I did a search for a replacement solenoid valve. It looks like the solenoid has been replaced with a pressure switch relief valve. Link below is for the instructions on replacing it.
https://production-pim-description-...naws.com/19910ddaedde76470f77e7459d641ff2.pdf
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yes, and your switch has a mechanical unloader on it that could be converted for use if your electric one fails . depending on the check valve to solenoid connection, it may need replacing
UPDATE: The compressor began operating correctly again. No more hum in standby mode. The motor would get hot after just seconds in the faulty standby mode. Now that the hum is gone, the motor no longer gets hot in standby. When it starts acting up again, I will resume troubleshooting.
OccupantRJ
Well-known member
I have an Asco unloader solenoid on the compressor I built from components, but the unloader solenoid I used is physically normally open at rest, so it is closed under power only when the compressor is actually running. At shutoff the power drops from the solenoid, it then goes open and dumps the head pressure. It would make no sense for a dump solenoid on an air compressor to be a normally closed type and electrically active when the compressor is not pumping.
Were you responding to The Cobbler's suggestion in post #7?
I am pretty sure the motor was the source of the hum, because it got pretty hot, even when the compressor cycled just one time to reach standby. If I didn't power down the compressor quickly after it started humming, it would not start again until it had cooled. When operating correctly, when the compressor goes into standby, the motor is cool to the touch.
American Locomotive
Well-known member
Your compressor wasn't going into standby/cycling off. It was likely on a bad circuit, and the motor was simply stalling as the pressure increased because it wasn't able to get enough power.