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Old 07-29-2012, 03:41 PM   #1
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Compressor fan motor or cap?


I noticed yesterday morning around 10am that the house seemed humid. Went outside to find a compressor just humming. No freezing on the lines or anything. Took a stick to the fan and while I could spin it, it never spun on its own. I powered off inside, pulled the breaker fuse, and removed the fan shroud. At this point I put everything back together and tried it again..and it worked great. I'm sure this was just the system being down, or me jiggling something.

Same thing this morning around the same time (I realize the shutdown might be happening much earlier and I'm just noticing it when I notice it). Powered off for 30 minutes or so which didn't help. Pulled the service panel, removed the capacitor which didn't have any signs of stress. No other symptoms of wiring issues so I put everything back together. Powered up and it worked like a champ.

So it seems to me that something is overheating. And the way it starts working for me is not because I'm wiggling the fan at the shroud or disconnecting/reconnecting the cap. Its because a certain amount of time has passed and whatever has overheated (fan motor?) has now cooled down. I'm inclined to go buy a capacitor but I think this is just me being cheap and wishful thinking.

fyi this is a 13 year old unit, coil replaced around 7 years ago, new condenser fan and cap replaced 2 years ago. Temps have been 100+ with plenty of humidity. It a carrier system.. air handler in the attic, condenser outside.
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Old 07-29-2012, 03:51 PM   #2
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Compressor fan motor or cap?


If you have an ohmmeter and a volt meter, you can test the capacitors yourself like in this video: http://youtu.be/2N_t6d0fSbw
If it is not the capacitor, I would say it has to be the fan motor. If the compressor was having problems, the fan would keep running. But if the fan has problems, and stops, then the compressor will go into bypass and overheat and shut down also.
Good luck!
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Old 07-30-2012, 09:37 PM   #3
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Compressor fan motor or cap?


So I think the thing on the left is a two terminal run capacitor. The thing on the right is a three terminal dual run cap. They are 7.5 and 40+5 mfd respectively.

I haven't followed the wires into the housing or wherever they go yet. I did notice there is no wire on the 'fan' terminal of the big cap. If neither of these is a start capacitor, do you expect that I'm probably going to find that they are wired together somehow?
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Old 07-30-2012, 10:08 PM   #4
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Compressor fan motor or cap?


The fan motor must have been replaced at one time, or the dual cap went bad for the fan side. The smaller cap should be for the fan.
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Old 07-31-2012, 06:46 AM   #5
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Compressor fan motor or cap?


While visual signs (bluging, leaking, etc) indicate a bad cap, there's no way to tell if your cap is otherwise bad without testing.

Given how cheap a 7.5 cap is, however, just pick one up at the local HVAC supply house and replace it. If that doesn't work, you'll probably have to replace the motor+cap again, but that's hard to say.
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