What is the purpose of a “start capacitor”?

A start capacitor is essential in single-phase electric motors, particularly those found in HVAC systems, as it provides the necessary initial surge of energy to start the motor. When the motor begins to run, it requires a high amount of starting torque, which the run winding alone may not be able to provide. The start capacitor temporarily increases the electrical flow to create a stronger magnetic field, enabling the motor to overcome inertia and start spinning.

Once the motor reaches a specific speed, the centrifugal switch or another mechanism typically disconnects the start capacitor from the circuit. This is crucial because, after startup, the motor operates more efficiently using just the run winding. Therefore, the role of the start capacitor is primarily focused on initiating motor operation rather than maintaining steady power, reducing noise, or preventing overheating, which are tasks associated with other components or different operational phases.