Sudden drop in motor speed on 919.165080

by Big Al
(Berkshire County, MA USA)

Sudden drop in motor speed while running, electrical cutout


I've had a Model 919.165080 compressor for about 15 years, never much of a problem. The other day, I turned it on, and while it was running, suddenly the engine speed dropped, as if the motor had just taken on more of a load (the pitch reduced as well), and then seconds later, the motor stopped running, it turns out because of an electrical circuit breaker.

I reset the breaker once or twice, and the motor still turns over, but seems to struggle doing so, and I believe is drawing heavy load at these times.

I took off the plastic cover over the electrical motor, and found that the plastic flywheel and piston turn over easily. There doesn't appear to be any resistance there. There are a pair of capacitors in front of the motor. One of them is somewhat browned, the other is (Painted?) black.

Any tips on what might be causing this problem, and what is needed to fix it, would be most appreciated. Thank you.

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Jun 02, 2015
You are welcome
by: Bill

It always gives me a charge when folks thank me for work they've done themselves!

What little help I was, you are sure welcome. Good for you in figuring out that it was the capacitor connections that were at fault, and that's a story I've heard more than one.

Have a good once.

B.

Jun 02, 2015
I got it running!
by: Big Al

After my testing effort with the capacitors, I concluded that there is really no such thing as negative resistance, that resistance, ohms, is always a positive value, ranging from zero (continuity) to infinity (disconnect) and anywhere in between. The behavior of the capacitors during testing seemed to be consistent with how I understand them to work. Further, it may be the case that the capacitor testing instructions were intended to suggest that when measuring VOLTAGE across the terminals after a slight charge, when switching the leads, that one might see a negative voltage during the discharge of the capacitor.

Anyway, upon the hypothesis that the capacitors were working OK, I spent time cleaning each of the terminals with a wire brush attachment on my Dremel tool, and painting each of the terminals and connectors with "DeOxit". One connector looked especially bad, and it wasn't even on the capacitor. It was at the front top of the motor behind a plastic tab, and from memory the wire was orange. The connector here was severely corroded, rusty, and I brushed this up and used DeOxit here as well. There are two capacitors one black and one white. The connectors on the white capacitor looked OK. The connectors on the black capacitor were caked up a bit with oxidation, and I cleaned these connectors as well. Finally, I found in the plastic capacitor housing a set of what look like automotive ignition points, and I used a point file to clean the contacts up a bit.

Upon re-assembly, it fired right up. In fact, there were for about 1/2 second a small shower of sparks at the rear side of the motor. I don't know what that was caused by, but all seems to be well now.

Thanks for the help.

Al

Jun 02, 2015
Capacitor checking
by: Bill

Not an expert in capacitors or multi-meters, Big Al. Sorry.

Happy to add this post in the hope someone with more experience in that can help.

No, I don't sell things, but my advertisers sure do.

Jun 02, 2015
Capacitor test results
by: Big Al

I found the helpful page explaining how to test the capacitors. I was not able to get a negative value on either capacitor (there appear to be 2, one for run and one for start?)

When I applied the digital ohmmeter leads to the terminals of the capacitor, the resistance seemed to increase gradually over the course of a couple of seconds to infinity. When I switched the leads of the ohmmeter around, it seems the resistance then fell gradually to zero and then back up to infinity, again over the course of a couple of seconds. I didn't see a negative value at all. I'm wondering if my ohmmeter is not capable of reading negative ohms.

Do you sell replacement capacitors?

Jun 01, 2015
919.165080 motor speed
by: Bill

First thing I'd check Big Al would be the motor capacitors, in particular because a discolored one usually indicates it's frying!

See the page on the this site about how to check the caps if you are not sure how and let us know how it turns out, if you would.

Bill

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