What are the most common causes of AC capacitor failure?

Residential air conditioning capacitor failure is most frequently caused by extreme operating heat, electrical power surges, and continuous mechanical stress. Capacitors are housed inside outdoor condensing units or indoor air handlers where ambient summer temperatures can become excessively high, causing internal dielectric materials to break down and leak. Furthermore, lightning strikes, grid power fluctuations, and brownouts create intense voltage spikes that stress the internal foil layers of the capacitor. Another common contributor is an aging compressor or motor drawing excessive electrical current due to worn bearings or dirty coils, which forces the capacitor to work harder than normal. You can prevent premature failure by keeping outdoor condenser coils clean. You can verify capacitor health by checking microfarad ratings annually with a multimeter.