How to Size Capacitors for a Compressor

By Lora Mortier

An air conditioner that is not working on a hot summer day is very annoying and even potentially dangerous. If you are able to determine that the compressor can be repaired by replacing the capacitor, it is a simple process to fix it. However, you need to make sure that you have the correct capacitor size. If you choose one that is far too big or small, the capacitor will burn out and can spray the liquid inside of it on the other components of the air conditioner. Fortunately, there are three ways to determine the capacitor size for your compressor.

Choose the correct capacitor size to repair your air conditioner.

Step 1

Consult the owner's manual for your air conditioner to see if it lists the capacitor size it requires. If it does not, call the manufacturer and ask what size it requires.

Step 2

Multiply the full load amps by 2,650. Divide this number by the supply voltage. The full load amps and the supply voltage can be found in the owner's manual. The resulting number is the MicroFarad of the capacitor you need. An MFD is a unit of electrical capacitance and will be written on the capacitor or its packaging. You can round up or down 10 percent to match the number to a capacitor size that is available. (This is a general estimate, not an exact figure.)

Step 3

Multiply the working power of the motor (it should be listed in kilowatts in your owner's manual) by the power factor in table 1 included in the Resource below. This will give you the exact size of the capacitor you need.