Compressor Motor Help

Gaffer

Gaffer

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A few years ago, I replaced the bearings in the compressor motor. It's been running fine. When I fired it up today, the motor only hummed and threw the breaker. The motor shaft spins freely by hand. All the wiring looks fine. Connections are all tight, and there is no evidence of heat. I haven't put my meter on the start and run caps yet but they look fine. I'm hoping it's just a cap, but I fear I lost one of the windings. Any thoughts or recommendations before I pull it off the compressor? It's a big'n and a pita to remove.
 
The start cap and the internal start switch are the two most likely suspects- easiest thing is to replace the cap first.
 
Gaffer said:
Yes. I have them exposed. Will check them tomorrow.
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Mind that I had situations when a motor cap measured fine with an RLC meter and still was bad at high voltage. I found the best way to check the cap is to buy a new one and try the motor with it...
 
Are you sure the compressor isn't seized or is just too stiff for the motor to turn it. If the tank is still holding pressure, you might also have a bad unloader valve. I'm not sure where you live in California, but if it's cold in your area the oil in the compressor could also be a problem. My older Kellogg compressor uses 30W oil. It doesn't like to start when the garage door is left open, and temperatures get below freezing.
 
projectnut said:
Are you sure the compressor isn't seized or is just too stiff for the motor to turn it. If the tank is still holding pressure, you might also have a bad unloader valve. I'm not sure where you live in California, but if it's cold in your area the oil in the compressor could also be a problem. My older Kellogg compressor uses 30W oil. It doesn't like to start when the garage door is left open, and temperatures get below freezing.
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It's not cold here. Nothing was seized, and my initial fear was the pump had. The first thing I did was remove the cage. I grabbed the belt and pulled and it easily turned the motor shaft and pump. There was no pressure in the tank as I keep the unit off until I use it. I have a small leak in my plumbing that I haven't tracked down, and it tends to come on in the middle of the night. I don't want to anger my neighbors as it stands outside on the side of my garage in a well-ventilated closet I built for it. It's a Husky Pro model with a 2-stage 7.5 hp motor with an 80 gal tank. I change the fluids at regular intervals.

As @markba633csi and @Flynth recommended, I'm going to order replacement caps today and hopefully, it will fix the problem.
 
+1 for changing the cap first, they don't last forever and are inexpensive enough that even if it's ultimately not the problem, it won't be a waste of money.
 
Another very likely problem is a stuck centrifugal switch. I have repaired quite a few motors with bad switches and they exhibit the same symptoms as yours. Sometimes the "repair" can be as simple as blowing it out with compressed air. On an open motor they tend to get pretty dirty. Just food for thought.
Ted
 
Have you checked the contactor points? Have run into that problem several times. Mike
 
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