Which of the following components is crucial for starting an AC compressor?

The starting capacitor is crucial for starting an AC compressor because it provides the necessary extra electrical boost to create a strong initial magnetic field. This is especially important for single-phase induction motors, which are commonly used in residential AC compressors. When the compressor is powered on, the starting capacitor momentarily increases the voltage and current, allowing the motor to start effectively. Once the motor reaches a certain speed, a centrifugal switch or a relay may disconnect the capacitor from the circuit to avoid any potential damage from overheating during normal operation.

In contrast, while contactors, pressure switches, and expansion valves play important roles in the overall operation and safety of the AC system, they do not provide the specific function of helping the compressor start. Contactors are responsible for controlling the power to the compressor when commanded to do so; pressure switches ensure that the system operates within safe pressure limits; and expansion valves regulate the flow of refrigerant into the evaporator. Each of these components is essential for the broader functionality of the cooling system, but the starting capacitor is specifically the component that enables the compressor to initiate operation successfully.