compressor wont turn on - buzzing sound

by steve
(kirkville ny)

my 12 gal. comp wont turn on. when i flick the switch,it buzzes like it wants to turn on but dosent

Bill says...

Steve, first, shut off, dump all the air from the tank, plug it in and turn it back on.

Any change?

If so, it may be your unloader valve.

If no change, visit the Troubleshooting page, and click the link to Will Not Start for more tips.



Comments for compressor wont turn on - buzzing sound

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Jul 06, 2017
Microfarad etc.
by: Bill

Unless you have a burning urgency to understand the terms, don't bother. If you do, Google define microfarad for lots of info.

As it says on the page I referred you to, make sure the ratings are the same on the new cap versus the old, regardless of the physical size of the cap. That includes the microfarad rating.

Sure, if you've installed a cap with different ratings it typically will not work.

Jul 05, 2017
by: David

Ok. The pictured one is the same CBBB60 bu the microfarad rating is 120uf. Could this mean the microfarad rating effects the output of power to the motor? I'm still assuming I put one in that was too small (even though physical size was correct) and it burned out.

Jul 05, 2017
Capacitor sizing
by: Bill

David, please see:

Jul 05, 2017
Humming and Capacitor
by: David

I had same issue as others with humming noise. Replaced capacitor with something similar. It started and I thought I fixed the problem. Second time it hummed again and a smell of burnt wiring was noticed. I can turn the mechanism by hand so I eliminated the idea it was seized. I'm about ready to order another capacitor rated for more power to the motor. Any ideas?

The the original capacitor had a rating of 60uf....whatever that means...the replacement one had a rating of 40uf so I am thinking it burned out.

Jan 15, 2017
Try this first
by: Anonymous

I took off the black covering and turned the flywheel several times by hand and plugged it back in. Came right back to life and still works. So try this BEFORE you take off the motor housing and draining the oil.

Jan 17, 2015
air compressor mortor has humming noise wont start
by: junior

Hi bill my air compressor motor have a humming noise wont turm on

if i give it a lil turn it ill go for 3, 4 sec slowing n turn off

i direct wire the outlet wire to the motor wire n does the same humming noise n everything

i can turn the pump n motor freely by hand ,if i turn the pump wheel by hand it pumps air

get dont know if its a bad overload switch or capaciter what does L1 n L2 mean on the motor wiring diagram from low to high voltage it a weg motor 7 wires 115 to 240 volts please help

Jul 31, 2013
Fixed this problem
by: Talavar

I just fixed this problem bud. just take the gear casing off (where you fill it with oil) Put a wrench against the gear inside and hit the wrench with a hammer (sideways) to free it up. this problem usually comes from running with too little (or no) oil. Might take a bit to free it (took me 5 minutes) but once it breaks loose, put oil on it, and turn the crank to work it down in to it. After that , just put it back together, and it works like a charm again.

Dec 21, 2011
connecting rod
by: steve

I took the pump apart and found the connecting rod is fused to the motor shaft.I took the cylinder off and it slid right off easily.The shaft does move,so I think the motor is OK.How do I get the rod off the the way,thanks for all your input

Dec 20, 2011
by: Buster

The way I understand your comments, you remove the belt from the compressor and you cannot turn the motor shaft by hand, that is a good indication that the bearings are frozen or something inside the motor has come apart and has the rotor in a bind, sounds like a trip to the motor shop. You could disassemble the motor and see if there are any foreign objects stuck in the air passages, another story.

Dec 20, 2011
by: Anonymous

I dont know what uncoupled means,when i try to turn the fan, it wont turn.The motor only has 30hrs or less on it


Sorry. If you don't disconnect the motor shaft from the pump, just because you cannot turn the shaft doesn't make it a motor frozen problem, it could be the pump is seized and that is stopping the motor shaft from turning.

Dec 17, 2011
wont turn
by: steve

should i be able to turn the motor? it does not it froze up?


If the motor shaft is uncoupled, and you turn the shaft by hand, and it won't turn, and it's a well used motor, then yes, you would have a motor issue I would say. I can turn any working motor shaft I have by hand.

Nov 26, 2011
Motor buzzzing
by: Buster

I'd put my money on the capacitor

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919.167310 Motor running - blows breaker

by Robert

Craftsman 919.167310 Motor running (But sounds different), Piston moving, but no compression and blows breaker

I have a Craftsman 6hp 30 gallon Air compressor. I have had it for 8 years. Never any problems till now. I plugged it in and started the compressor. It ran like normal for 1 minute then blew breaker. When restarted, the motor was very quiet and will flip breaker after 15 seconds of running. I took the cover off and replaced the compression ring with a new one, then reassembled. Same issue. The tank has 0 pressure, and I even tried starting with the drain valve open for kicks, but no good. Motor seems to spin fine, moving piston as it should but no pressure and substantially quieter. Help!


Robert, when you replaced the piston ring, did you examine the valve plates and the gaskets?

A blown gasket would make a change in sound, as would a valve failing.

The popping the breaker is electrically related, of course, and that may or not be connected to the noise change.

An overload motor will pop the breaker, and that could be the result of back pressure, mechanical issues, intake filter being plugged, check valve not operating properly, capacitor weakening, or the motor itself failing, among others.



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