What is the common cause of capacitor failure?

The single most common cause of premature residential HVAC capacitor failure is extreme operating heat combined with electrical grid stress. Capacitors are housed inside outdoor condensing units or indoor air handlers where ambient summer temperatures can become excessively high, causing internal dielectric fluids to boil, expand, and break down over time. Furthermore, lightning strikes, grid power fluctuations, and brownouts create intense voltage spikes that puncture the delicate internal aluminum foil and dielectric film layers. Another frequent 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 component health by checking microfarad ratings annually with a multimeter.