To start electric motor start and run capacitors on a single phase motor, turn the switch fully clockwise and then release the switch. While both capacitors engage at start-up, the start capacitor runs only momentarily. The run capacitor operates continuously, adjusting current and windings to maximize motor efficiency.
The start capacitor gets a motor started by giving it a push in the form of a high-torque, rotating electrical field. When the motor reaches a certain speed, usually about 75 percent of its full load speed, the start capacitor disconnects. The start capacitor connects back to the motor's electrical circuit if the motor drops below the required speed. The run capacitor is designed to work continuously. Always connected to the motor's electrical circuit, it ensures the motor runs at full power by varying the voltage based on the motor's load.
Problems with either type of capacitor can cause the motor to stop running. When the motor clearly has a power source, but does nothing, the run capacitor is most likely burned out. A burned out start capacitor may develop a cracked casing or look misshapen. Both start and run capacitors store energy. To remove the charge when working on one of these components, use an insulated wire or plastic-handled screwdriver to short the two leads.