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Old 04-17-2013, 10:05 AM   #1
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Capacitor question


Can a capacitor change out effect the way a running unit sounds upon startup?

In other words, is it just my imagination but we just turned on the downstairs AC for the first time after the winter months and after doing a preventative strike of replacing the capacitor, it sounds quieter. 4 ton Rheem unit and the funny thing is I have 2 identical units, saw them unboxed when they were installed and they both had different caps in them from the manufacture.

Is this possible, sound operation and noise change? replaced cap was about 10 years old.

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Old 04-17-2013, 12:14 PM   #2
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Capacitor question


The capacitors are used to "start" the motors both for the fan and the compressor. "If" the replaced capacitor is an exact replacement for size and rating then it's possible the old one was getting weak.

The other possibility is that the one you replaced was an "Optional" hard start version for whatever reason. This could change how the unit runs.

Then of course there is the Murphy Law factor that comes into play that says that just because you touched it things decided to change on their own.

Also...... depending on the load on the two units, meaning the temperatures and humidity indoors and the temperatures outside, it could just be that one is working a little harder than the other.

There are a whole list of things that can make two identical units in the same home work and even sound different.

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Old 04-17-2013, 01:39 PM   #3
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Capacitor question


good idea to replace the cap as they fail on the hottest day. same units but they may be different if the serial #s are different. may have slightly different compressors depending on the production run.

what you really should do is remove the condensor fan and backwash water thru the condensor coil with a garden hose/sprayer as that is the only way to clean that unit properly.
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Old 04-17-2013, 04:06 PM   #4
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Capacitor question


Quote:
Originally Posted by yuri View Post
good idea to replace the cap as they fail on the hottest day. same units but they may be different if the serial #s are different. may have slightly different compressors depending on the production run.

what you really should do is remove the condensor fan and backwash water thru the condensor coil with a garden hose/sprayer as that is the only way to clean that unit properly.

Have done that also, thanks!
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Old 04-17-2013, 09:58 PM   #5
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Capacitor question


these are run caps, not start caps. they start and run the motors. start caps are huge mfd, usually in the hundreds of mfd's.

run your own test. check your refrigerant pressures with your normal cap. then run it with one 10 or 15 mfd higher or lower and check your pressures again. the compressor will run at a speed correlating to the cap, thus your pressures will change all because of the run cap in use.

lower the run cap and compressor stands a chance of over amping.

"Start caps are actually electrolytics which are designed for operation on ac. These have a limited number of starts, and are only allowed to be in the circuit for a few seconds.

Run caps are actually oil-filled caps. These have a virtually unlimited lifetime, and are allowed to be in the circuit continuously.

Start caps have a very high capacitance to volume ratio.

Run caps have a low capacitance to volume ratio."

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