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Why does a motor or compressor need a capacitor to run properly? What actually does a capacitor do?

worn out capacitors

Question: Why does a motor or compressor need a capacitor to run properly? What actually does a capacitor do?

Thanks for your interest in our website! Great question! You can get into a more complex answer for this question, but my heating and air conditioning teacher in vocational school explained it in a simple and in the following way: On alternating current (AC) the current alternates on the voltage from zero to 110 or from zero to 220 volts 60 cycles per second. The run capacitor throws a stored charge in there when the voltage reaches the zero point and keeps the voltage steady instead of all the up and down voltage drops. This makes the motor or compressor run smoothly and more efficiently. This is easily seen on an old oscilloscope where you can see the AC current going up and down. 60 cycles per second are pretty durn fast! It is amazing! Capacitor failure is a major problem for air conditioning and heat pump systems. We recommend keeping an extra capacitor on hand in case your capacitor goes out on a hot summer day or cold winter night. We suggest having a spare capacitor for the air conditioner and a spare capacitor for the fan blower motor. We sell capacitors on the following page:  Please click here to see the capacitors that we sell.  We would be happy to look it up and see what capacitor that your unit uses in one of our parts programs. Please send us your unit’s model number if you would like to find out what capacitor that the manufacturer recommends. Our email is We have a really good YouTube video below made by David Jones that explains why we need capacitors in HVAC systems. Thanks so very much to David Jones for making this excellent video! I hope this answers your question.  We hope you have a great and blessed day! We Would Love to Help You Out and Earn Your Business! 
Sincerely, Steve Arnold

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