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Question: What to look for when a capacitor is bad

Question: What do I look for if I think a capacitor might be bad?

Here are some things that you can look for if your capacitor is bad. The Air conditioner outdoor unit will not come on. Either the outdoor fan does not run, the compressor does not run, or both the fan and the compressor do not run. You checked and reset your breaker and the outdoor unit still does not come on. You can here a little humming sound inside the unit which is the low voltage contactor humming. You pull the disconnect and disconnect the power to your outdoor air conditioning unit. Please make sure your electrical power is off before working on any air conditioning equipment. You take the door or cover off your outdoor unit’s control box and find a bad, swollen run capacitor. EPA stopped allowing manufacturers to produce capacitors with cancer causing PCB’s. Since they stopped allowing the use of PCB’s the capacitors now have a shelf life. Many times I see capacitor problems that will not allow the compressor or the fan to come on. Many times you can clearly see that the capacitor is bad because it is swollen or even blown apart with capacitor oil everywhere! Sometimes you need a special meter to test the microfarad (MFD) or UF rating. A capacitor testerPlease click here if you are interested in the capacitor testing meter we sell. “MFD” and “UF” mean the same thing, “Microfarad”. Many times you will see an “UF” rating on the capacitor instead of “MFD.” Yes, these two abbreviations mean the same. Most of the time you can tell that a capacitor is bad because it will be swollen up. Please see the picture below for the comparison between a good and bad dual run capacitor. We call them dual capacitors because the capacitor helps run both the fan and the compressor.
*Tip: When identifying the capacitor that you have, you might see the rating stated in “MFD” or “UF.” “MFD” and “UF” mean microfarad rating and mean the same. We sell many different capacitors on the following page: Please click here to see the capacitors we sell. Please email us anytime if you would like for us to look it up and see which capacitor your unit uses. Our email address is: We would Love to have Your Business!!


Bad round dual capacitor on the left. Bad oval capacitor on the left.
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