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Old 02-16-2009, 07:51 AM   #1
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Smile Need help with capacitor rating

I have a 70 27' overlander with original AC that quit running late last year. The unit quits after a short time probably when the over temp swith in the compressor trips. After reset it tries to start again and a few seconds later quits again. I feel confident that the capacitor is probably bad and would like to order one today since I have to order one for a well pump motor that went bad.
My question is does anyone know the specification Cap/volt and if there is any constraints as to the physical size? It sure would be nice not to have to get on top and check it out in this cold.

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Old 02-16-2009, 08:53 AM   #2
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Well, if I hadn't thrown out the guts of the last one I replaced...

Let us know if that really is the problem. It seems to me that if the motor gets up to speed before it quits, then the cap isn't the problem. Isn't the cap only necessary to start the motor rotating?


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Old 02-16-2009, 01:01 PM   #3
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Yes you are right if it was starting. The fan is starting but not the compressor. the thermal bi metal swith opens after maybe 10 seconds and then after cooling it resets and attempts to start again if my memory is not failing me again.
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Old 02-16-2009, 01:28 PM   #4
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As I recall from H.S. electrical shop class: The capacitor is used in many motors to compensate for a phase shift between voltage and current when starting the motor. There is a power factor due to the voltage and the current getting out of phase with each other. That means they are not in sync because the motor’s coils creates a current lag and the capacitor is added to create a compensating voltage lag.

Also since the motor starts and then stops, plus the AC unit appears to be old and could have many hours on it. Therefore I doubt the problem is with the capacitor. I would check the motor itself to see if the shaft or rotor, or bearing are worn out or it is vibrating which might cause heat build-up which might in turn activate the heat sensor which shout down the motor. You may need a new motor assembly.
I may be wrong, so let us know when you determine the cause of the problem. Good Luck
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Old 02-16-2009, 02:04 PM   #5
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Sounds like an inadequate extension cord, or a problem with the source of power.

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