How to Diagnose a Weak Air Conditioner Capacitor

Turn on the air conditioner. Go outside and stand next to the compressor. Listen for a humming noise, which signifies that your capacitor may no longer be working at full capacity.

Compare recent power bills to older power bills. If you notice an increase in your power usage yet your habits have not changed, this could be a sign that your capacitor is failing. As a capacitor weakens, it puts greater stress on the motor, causing the system to consume more electricity to function.

Turn off the power to the air conditioner. Open the electrical access panel on the side of the condenser. Examine the capacitor. The top and bottom of the capacitor should be flat. If either is bulging, the capacitor is either dying or already dead.

Lay a screwdriver across the capacitor terminals to discharge any stored power. Even if your capacitor is weak, it can still store electricity and shock you if you do not discharge the remaining power in the unit. Hook a multimeter up to the capacitor terminals. Set your multimeter to "capacitance" and take a reading.

Detach the three wires connected to the top of the capacitor. Hook a multimeter up to the capacitor terminals. Set your multimeter to "capacitance" and take a reading.

Compare the capacitance rating, which should be shown on the multimeter's screen in microfarads, with the microfarad output listed on the capacitor itself. A significant difference in the microfarads that a capacitor puts out and the microfarads that are listed on the unit signify a problem.

Set your multimeter to "voltage" if it does not have a setting specifically for capacitors. Test the voltage of the capacitor and compare the voltage to that listed on the capacitor itself. A weakening capacitor will display a lower voltage reading than that listed on the unit.