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Postby kingfisher45 » Sun Jul 24, 2011 1:01 pm

I just put a 45/5 microfarad capacitor to replace one that was 45/7.5 and the system works. Does that mean the previous capacitor, which itself was a replacement, was the wrong one? i
If not why is the 45/5, the 5uf being for the fan, capable of operating the fan? Can this substitution cause a problem?
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Postby 4ftBanger » Tue Jul 26, 2011 8:00 am

Single phase electric motors need a capacitor to energize a second-phase winding. If the wrong run capacitor is installed, the motor will not have an even magnetic field, and this will cause the rotor to hesitate at those spots that are uneven. This hesitation can cause the motor to become noisy, increase energy consumption, cause performance to drop, and cause the motor to overheat and fail. Additionally, the motor may not run at the correct speed or have the proper horsepower to move the right quantity of air through the coils. The capacitor itself can become overheated and prematurely fail.

The motor should have a rating tag on the housing indicating horsepower and capacitor requirement.
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Postby heatseeker » Tue Jul 26, 2011 8:31 am

in other words it will appear to run normally but it isn't causing internal damage.
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Postby nomadpeo » Thu Jul 28, 2011 6:32 am

ten percent tolerance is a good rule of thumb. if the motor is rated for a 7.5 mfd, anything under 6.75 too small. you can disconnect the 5 side going to the motor and connect that wire to a single 7.5 mfd cap. the other terminal on the new 7.5 mfd should be connected to the 'c' terminal on the 45/5 you installed. in this way, you are deleting the 5 and replacing it with the 7.5. as 4ftbanger said, look at the name plate on the motor itself for the correct size. if you can't make it out and it is the original motor, you can call the supply house that distributes the brand of ac you have and give them the model number of the condensing unit and they should be able to tell you.
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