My compressor makes a low humming sound when I turn power from off to auto. What could it be?

It is not ideal having a power strip due to the amps it draws, but the fact it hums, leads my to believe that the start/run capacitor on the motor might be failing.

Please realize I'm not a professional compressor repairman.

Your description "comes on for a few second, makes a slight humming sound, then goes silent" leaves me guessing. When you say "comes on" does that mean it "makes the pumping sound of a compressor" or it "Clicks"? Allow my musings.

On a plugged in and turned on compressor the compressor's pressure switch turns on the pump motor when the pressure falls below it's set low pressure threshold (usually ~ 90 psi). The pumps pushes air into the pressure tank until the pressure reaches its high pressure threshold (usually ~ 120 psi). If the compressor is not plugged in or turned on you can hear a click when the pressure switch turns on.

Aside: Leaks, of any sort, make the pumping more frequent or longer. Bad leaks can make it pump continuous because the high pressure threshold is never reached. The leaks can be in the switch, at line connections or in the pump (valves or piston rings) itself.

I once had a low-volume ultra-quiet compressor that made little more noise than a hum when compressing. If yours is not an ultra-quiet (clicks on, hums, and quits) than I'd have to guess that the pump might be binding instead of pumping. If it is binding then the motor would over-heats and shuts off.

Some compressors are oil cooled. If an oil cooled compressor was extremely low on oil would it bind? I suspect so.

If you suspect binding I'd find a parts list for your model to work from and disassemble the pump to investigate. (see link below)

That's my best guess on limited information. Good luck.

Campbell Hausfeld Air Compressor Parts

The best guess is that you have a bad thermostat. When the compressor shuts off it has to stay off for a long enough period of time for the low pressure high pressure to equalize. If it turns the compressor off and back on immediately it can't start against the heavy load created by these unequal pressures. If it will start every time after sitting for 10 minutes the thermostat is making it short cycle.

Could be a couple of things, first, a cord, It might be a 20 amp breaker but if it goes through a cord, it loses amperage and will not start. It needs about 16 amps to start and then about 13 to run. Will it start by being plugged into the wall? Second, let the air out and see if it will go, too much back pressure, not enough power. third, make sure it is warm, We used to heat a bathroom on the job just for the compressors in the winter, of course we all went in there to at break time, only warm spot in the house. And last, If the capacitor is bad, it will lose it's power, but I would check the rest first. Hope this helps.

sounds like it has ran low on oil and has siezed,sorry man it's probaly toast.

sounds like you experienced an ice over. this can destroy the compressor. if contactor is humming the call for cooling is present but the breaker poping is cause for concern. possibly needs new compressor.

"Pop" My friend, you already know the answer. "POP" relay, relay, relay..........You have a good sense of humor..

It is definitely with the compressor. It should more like you may have a weak winding in the compressor, you can a hard start capacitor (sp5 ) that will help the compressor on restart. Note that this is a last chance solution for a compressor.

Ifs its a small humming sound,then its the contactor pulling in. But if it a loud humming sound then its the compressor kicking in. and the fans not, try to take something long and turn the blades on the fan, if it takes off and run then your capacitor is shot or swollen at the top,which was cause by power surge. Take-off and replace with the same mfd. writings ,on the outside of can. Also check for blown fuses or tripped breaker . the fuses should be in the disconnect box on the wall, or the breaker in the breaker box.. Older house has fuses instead of a breaker box!

It is probably either the Compressor and or the capacitor that has failed. The compressor will hum and pull a lot of amps when it has seized up. Sounds like it is time for a new unit.