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The A/C unit is just humming could it be the capacitor

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Take a look at the capacitor. If it is swollen, rusty, puffed up on top, or leaking it is bad. Sometimes you cannot tell by looking at it so you can test it. Using a suicide cord attach the aligator clips to the capacitor, Place the cap where if it explodes it's remains won't get on you.
TIP: (check to see if the leads are shorted to avoid any minor explosions.) Plug the cord into a 120 volt outlet for 3 seconds. This charges the cap. Tap the cap on an iron surface to discharge it. If it makes a popping sound it is good. If it does not hold a charge it is bad. Another way is to check it with an analog meter. Set the meter on the most sensitive setting. Touch the leads to the discharged cap. The needle on the meter should hop; reverse the leads and retry it should hop again. That is an indication of a cap that will hold a charge. If the needle never moves of course that is a sign the cap is bad. Also if the needle goes all the way over and stays, that is an indication the cap is shorted and therefore bad. The cap is designed to boost the power to the motor to get it going with multiple windings being powered up at once. As soon as the motor reaches running speed the cap drops out of the circuit and it takes half the power for the motor to continue running at optimum speed. This saves energy.
FYI: The old style shaded pole motors had no capacitor and so they used twice the power to do the same job.

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Posted on Jun 30, 2009


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