purpose of run capacitor

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Old 05-11-12, 01:36 PM
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purpose of run capacitor

I have an AC, the AC tech told me currently the capacitor is at 75% of full capacity. I am debating if I need to replace it to avoid issues to the compressor.

I was told if the run capacitor is not near full capacitance (like +/- 5%), it will be hard on the compressor and compressor will burn out faster.

I am puzzled by this statement. Once the capacitor helps the compressor to get started, why it is neede later?
the word run seems to inciated it's needed.

but can anyone explain to me how this works?
 
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Old 05-11-12, 03:36 PM
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There is always a run capacitor on a single phase compressor and you may or may not have a start capacitor and relay as well.
The run capacitor must be within it's designed operating specs, and as you mentioned 5%. As current flows through the run capacitor and the start winding, it causes a phase shift of the motorís current, thus improving the power factor of the motor. When the capacitor fails or is weak, this will cause the compressor motor to draw higher amperes, run hotter and eventually burn the motor or damage the start winding.
When a capacitor begins failing (usually due to heat), the MFD usually goes down reducing it's capacity- meaning it will most likely fail completely soon or worse, the compressor.
I highly suggest replacing the capacitor with the same one quickly.
Be sure the voltage rating is also the same or higher. A 370v can be replaced with either another 370v or a 440v one, but a 440v one must be replaced with only a 440v.
Capacitors are inexpensive compared to a compressor.

If you have a start capacitor and start relay, you may not know your run capacitor is bad until a failed compressor- since the start capacitor will allow the compressor to start, yet the compressor will over amp and run hot with a bad run cap until it fails.
 
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Old 05-11-12, 09:12 PM
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thanks for the explanation. I will order the capacitor and replace it soon.
 
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