How to Check Capacitors With a Multimeter in A/C

Turn the A/C unit off along, and unplug it from, the wall to prevent any power surge to the unit when handling the internal devices. Locate the capacitor inside the unit. Capacitors will come in varying shapes; some will look like either a round or oval cylinder with two or three power terminals on the top. Air conditioners can have two capacitors -- one for the condenser fan and one for the compressor -- and are called dual-run or dual-rated capacitors.

Place the probes on the terminals for a run capacitor with two terminals. If the capacitor is a dual-run capacitor with three probes, connect one probe to the herm terminal and the other to the common terminal. You can check the capacitance of the fan for a dual-run capacitor by connecting the probes to the fan and common terminal.

Turn on the multimeter and read the display screen. You will see two readings, one for the condenser fan and the other for the compressor. Readings will be in micro farads and seen as the letters "mfd" or "uf."

Replace a capacitor if the reading is below manufacturer standards. You can find the required micro farad for the capacitor either marked on the device or in the air conditioner's installation manual. Refrain from testing any capacitor if it is leaking, has corroded terminals or the capacitor unit bulges. Replace it immediately.