921.153640 motor runs then sparks fly

by Dennis Keeler
(Kingston Ma.)

Craftsman air compressor model 921.153640,1hp,7gal, little or no use since new.


921.153640 motor runs then sparks fly behind the fan then circuit trips.

Started the unit today and engine would try to turn, did this over and over then finally kicked and ran filling the tank to capacity. I repeated this a few times then it sparked in front of the fan and tripped the circuit.

Attempting to start again and we are back to not turning over, wants to but will not. I notice a yellow circuit board where sparking occurred, it looks like there are points, it looks a bit black and sooty in that area. Any thoughts. Thanks Den

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Jan 02, 2017
921.153640
by: Doug in s.d.ca

Den,

As Bill said, we really appreciated the updates.

It's frustrating when people come in and we try to help, but get no feedback.

Thanks,

Doug

Jan 02, 2017
Site & Doug
by: Bill

Den, the site is the vehicle, Doug's done all the help.

Regardless, thanks for visiting, for taking the time to work back and forth, and for your kind comments about the site.

Jan 02, 2017
motor runs then sparks fly
by: Den

Took the fan and centrifugal switch off and found that the contact plate had become welded together. I used a hacksaw and carefully separated the section ,cleaned and reinstalled and the compressor starts every time. I have ordered a new contact plate and that should be the long term fix. Thanks to Bill for your terrific support site and Doug for all the great advise. Den

Jan 01, 2017
motor runs then sparks fly
by: Den

Hello Doug, Had some time today and took apart the switch and that is 99% of the problem. The points on the contact plate are welded together and as you suggested the motor only starts after warming up by tripping several times. Now on searcdh for a new contact plate,its not listed in any of the Craftsman diagrahms. Thanks Den

Dec 31, 2016
motor runs then sparks fly
by: Den

Thanks for staying with me on this problem Doug, and I believe you are right on with the switch caps. This is the area that will spark once in a while and it is a bit scorched looking. The caps are definetly apart.On the diagrahm /parts list it is not shown that this part can be purchased.How would you suggest I go about solving this,should I try to gently persuade the caps closer together or can you think of another solution? I had the compressor up and running today,it took about 5 or 6 trips but then it started up and ran well, pump and engine run really strong. Sometimes after the psi drops the motor will start right in, other times it trips,
frustrating. Thanks again Den

Dec 30, 2016
sparks fly
by: Doug in s.d.ca

Yeah, this is unusual.

Now, though, I'm thinking maybe the centrifugal switch is the problem. That would be where the sparks are from, so maybe a close look at that may reveal a problem.

Normally, the contacts are closed, and disconnect the start cap after the motor gets going.

This sounds like the contacts aren't closing, so there's "no" start cap at that point.
Then after it trips once, and there's been some action at the contacts, they close, and *then* it stars OK.

Dec 30, 2016
motor runs then sparks fly
by: Den

Just picked up a new start capacitor, replaced the original and still same no start and tripped breaker, put the old one back in and started right up. Can always get it back going after a couple of breaker trips, crazy.

Dec 30, 2016
motor runs then sparks fly
by: Den

You could be right about the breaker being weak, i also have a 5hp air compressor that starts right up on that same circuit w/o issue. I checked both start and run capacitor with meter and they both appear to be sound and functioning properly but i am going to pick up a new start cap as you suggested. It seems that each time that the compressor trips the circuit and i reset, the compessor starts right up,so maybe its the breaker Thanks again for your assistance.

Dec 29, 2016
sparks, trips, capacitors
by: Doug in s.d.ca

It's entirely possible that 20A isn't enough to start it, and/or the circuit breaker is weak, or, more likely, the start cap is going bad.

If you haven't already, I strongly advise checking them, especially the start cap.

Dec 28, 2016
motor runs then sparks fly
by: Den

Thanks for your input Doug. Actually got the compressor running and filled tank to capacity.After dumping the air the next time i would start it would trip the 20 amp breaker,this would keep going on and every other time i would get motor running and the tank filled and working the next time it would trip again. Runs great when running just cant get it to stop tripping at start up. Is it possible that the 20 amp is not enough to start the engine? doesnt seem right with only a 1 hp motor. Thanks for any help Den

Dec 27, 2016
921.153640
by: Doug in s.d.ca

(The 921.153640 manual has the worst troubleshooting section on motor won't start that I've ever seen)

First thought was this was a brush motor - but it's got capacitors, and the points are probably the centrifugal switch for the capacitor.

I think if you check the caps, you'll find one or both are bad.

http://www.about-air-compressors.com/testing-capacitors.html

Good luck

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wiring motor and switches

by Wayne
(Canada)

Rewiring my Craftsman

Rewiring my Craftsman

Took my compressor apart to fix it, now I don't know where the wires go from the brushes, motor, pressure and shut off switches.
The ground wire is the only thing attached from the plug coming in, because it is not a spade connector.

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Aug 06, 2016
sorry, no pics
by: Wayne

Fuse and cap are integral to motor, which by the way is identical to the one which came out of my Porter-Cable oil less pancake style of compressor.
Unfortunately it is also in pieces and wires disconnected.
It should be very simple as there is only 3 wires in, and one yellow short length still attached to one of the brushes. I assume it goes to a terminal on the cut out switch.
Another shorter black wire goes from the cut out switch to the power switch.
Again I assume that the black line in goes to the power switch and the white in goes to the other brush. Simple....., Yes?
Real tight quarters to even clip on spades during reassembly, so I just wanted to be sure that I won't fry anything and have to take it apart again.
Thanks for all the help. I will try to take a picture and post it over the weekend, and once I've figured it out..., this should serve as a reference to all us people with old-timers disease that have trouble remembering to mark things down, let alone trying to figure out where all those spare parts came from and where they go.

Aug 05, 2016
Bummer
by: Doug in s.d.ca

Does it have a model number?

Failing that, can you get pictures?

Does it have external caps? or are they integral to motor?

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