Craftsman compressor won't start!

by Chuck
(Langley AFB, VA)

I have a Craftsman compressor, 1.5 HP 3gal model 921.153101. It is about 2 years old and it has been hardly used. The air filter and oil are good. I went to start it today and it makes a humming noise but doesn't run. The back of the motor gets warm and the fan on the front moves a little but it won't pump up. I turned the blades and they rotate easily. The switch looks good and I can seen the contacts touch. Any ideas?





Bill answers...

Howdy Chuck. Welcome to you and all your wingers at Langley AFB.

While I'm no electrician, I'm thinking that the "humming motor" tells the tale.

The motor is trying to start, but can't. That it freewheels suggests that it isn't bearings, but as far as I'm concerned, you've got a motor problem.

Don't forget the motor-starter / capacitor on your motor. That holds a reserve of power that is used by the motor when it starts, as it draws most amps on inrush when the motor is trying to start.The capacitor adds amperage on start-up helping the motor get going.

I'm guessing it's your capacitor or the motor itself.

Now, all that holds true if it's the motor that's humming.

If it's the pressure switch that's humming or buzzing, you've got point issues and it's time to replace the pressure switch.

I'm going with the motor capacitor.

Cheers,

Bill




Comments for
Craftsman compressor won't start!

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Sep 26, 2010
 Craftsman compressor won't start!
by: DA

Craftsman compressor, 1.5 HP 3gal model 921.153101 will not start.
- Hums when turned on then clicks off.
- Wire insulation to motor capacitor appears to have a burn mark.
- Electric motor shaft will not turn even when wrenched.
- Motor shaft gets hot if multiple start attempts are tried.
- Pulled the pump cylinder head and outlet tube to the check valve, but pump was not loaded

From what I have read, this sounds like an electric motor failure because the motor shaft does not turn.

Any other ideas?
Sep 03, 2009
 Craftsman Compressor Woes
by: SS

I have the same compressor and the same problem of not starting except that the blades won't move on the motor. I also get the humming sound of the starter switch and an occasional clicking sound but no starting of the motor, hence no build up of pressure. The pressure valves work to release what air used to be in the tank. Is there a way to tell if the starting motor capacitor is shot without actually replacing it? Is there a way to tell if the motor is seized up without disassembling it? I have looked over the reviews of this unit by other buyers and there are many unhappy people whose units have done the same thing as mine/yours. Any help is appreciated before this becomes a doorstop.





Bill likes doorstops!

Howdy SS. Thanks for visiting and commenting.

Doorstop hmmmm? Might be a plan. The problem (aside that most are made in a foreign land out of recycled pop cans etc.) with the lower cost compressors is that they are that, low cost.

Taking one to a repair depot means that you're being charged what... $30 - $40 an hour for a technician to examine, diagnose, and fix a compressor that may have only cost $150 to start.

I'm guessing capacitor still, but it may be that the motor is gone.

Check with your local garage (if you can find one that still fixes cars) and ask if they can check a capacitor for you. Or, check out your local motor rebuild shops and take the unit to them to check that and the motor.

Regardless of what they find, it's going to cost you some money.

So, maybe it's better to spray paint it a pretty color, and park it in front of the door! :-)

Cheers,

Bill
Aug 31, 2009
 Same deal here. Probably a compressor motor
by: Anonymous

I have 4hp 25 gallon craftsman 120v Air compressor. i got 2 issues first off it DID say don't use ext. cords but since it wasn't my air compressor and was borrowed i didn't read that.

was missing gauges and some filter for the intake to the oil-less compressor. i used it with extension cord for 4 months would pump up the air till pump slowed and would cut it off via the switch. one day it got slow using a diff outlet and i kept it on till it didn't push air then i also thought i could put pb blaster oil in the hole to compressor to free the oil-less piston up but it didn't work and saw do not use long ext cords trying to see what was wrong with it.

so i then plug it in without ext cord and oil dripped down i think into the motor and it started running really fast then started to smoke.

so i shut it off then waited then ran it some more later hoping the oil would run out and it didn't and smoked more. well now it doesn't turn and hums when i turn it on. i would replace the motor but don't know where to get a compressor motor.

its not my air compressor and i don't have 300 bucks to buy a new one. Couldn't i just buy another air compressor and still use the tank..is there a difference between 1.5 hp and 4hp or is this easier just to fix this one.





Bill comments...

Thanks for adding your comments to this post.

I'm not quite sure what it is you did, but it sounds like you put oil into an oil-less compressor? Is this right?

And now, when you turn the compressor on, the motor shaft won't rotate, and the motor sits there and hums. Eventually it would go off on thermal overload, I would think.

First off, try to disconnect the shaft from the compressor pump and see if the motor runs without a load. This is, it starts and runs without a hum. If so, it's possible that adding the oil to the oil-less compressor has caused the compressor pump to change load characteristics, and you've overloaded the motor as a result.

Yes, there is quite a difference between a 1.5 HP and a 4 HP compressor in output. Remember, one HP of motor equals about 4 CFM of air at 90 PSI.

Yes, you can just buy a new pump and use the motor (if it works), the tank, and the accessories from the old compressor to try and save some money.

Keep us posted as to your developments, will you?

Thanks,

Bill
Aug 15, 2009
 Don't use an extension cord if possible . . .
by: Paris

I have the Sears 921.153101. It began starting "funny," like at half speed and shaking etc.. Sometimes it would then go to normal running, often not. I initially thought it was the capacitors. It wouldn't do it every time, but often enough. Took it in the basement to work on and it worked fine. But outside in the garage it would do the stumbling startup thing. Then I figured out the difference between the basement and the garage.

In the garage I had an extension cord in the circuit. Removed the extension cord and no problem. The extension cord wasn't a thin household type either. But apparently the gauge wasn't heavy enough. I'm pretty sure it's a simple amperage flow issue and if the gauge is too light, not enough amperage can flow to run the motor smoothly. It's been 100% since eliminating the extension cord. The manual also says not use extension cords . . . duh.

___________________

Most excellent advice. Amps is power, and it's like gas to an engine. If the gas line is too small, not enough gas can get to the engine to run it right.

If the electrical extension cord is too small (say an 18 gage versus a 12 gage wire), your electrical motor doesn't get enough amperage (gas) to run right.

Thanks,

Bill

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