Run capacitors provide the necessary phase shift to create starting torque and maintain running efficiency in single-phase PSC motor windings. Over time, the dielectric fluid inside the capacitor degrades due to voltage spikes and high ambient heat. A capacitor is considered failed if its measured capacitance drops below 10% of its rated value (e.g., a 45 µF capacitor measuring below 40.5 µF must be replaced). Operating a compressor with a degraded capacitor increases current draw, elevates winding temperatures, and trips the internal thermal overload protector.

Contactors act as the heavy-duty electrical switch delivering line voltage to the compressor and condenser fan motors. Each time the contactor closes, a small electrical arc occurs across the silver-plated copper contacts. Over time, this arching causes 'pitting' or carbon buildup, increasing electrical resistance across the contacts. In severe cases, the contacts can weld together, causing the compressor to run continuously even when the thermostat is satisfied. Technicians must inspect contacts for pitting, measure voltage drop across closed contacts (should be less than 0.1V AC), and test the contactor's low-voltage coil resistance to ensure reliable pull-in.

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