How To Wire Up A Start Capacitor

By Robert Sylvus Mar 2, 2011 9:01 pm EST

Large electric motors with a high starting torque, like an air conditioner's compressor motor, often use a start capacitor kit. A start capacitor kit contains a start capacitor, relay and wires. The start capacitor gives the motor's windings an electric boost during the start-up phase. The relay disconnects the start capacitor from the motor's electrical circuit once the motor has reached operational speed. The wires on a start capacitor kit use color-coded insulation and connect to the motor's run capacitor and a contactor — the relay supplying power to the motor.

Step 1

Turn off the electricity to the unit the motor operates. Unplug the unit if it connects to a wall receptacle. Turn off the unit's circuit breaker if the unit wires directly to the circuit breaker.

Step 2

Inspect the start capacitor's wiring diagram. The diagram identifies the capacitor and relay's wire color and the wire's function. Often a stamp on the side of the relay shows the wiring diagram.

Step 3

Push the wire terminal on the start capacitor relay's "Common" wire, usually the black wire, to the common terminal on the load side of the unit's contactor. The wires connected to the motor's common terminal, marked "C" or "COM" on the motor's wiring chart, also connect to this contactor terminal.

Step 4

Push the wire terminal on the start-capacitor relay's "Run" wire onto the run capacitor's "HERM" terminal. The wire connected to the motor's start terminal, marked "S" on the motor's wiring chart, also connects to this run capacitor terminal.

Step 5

Push one of the wire terminals on each of the short wires in the start-capacitor kit onto the start capacitor's terminals. One wire goes on each start capacitor terminal.

Step 6

Push the terminal on one of the start capacitor's wires onto the start capacitor relay's "Start" terminal.

Step 7

Push the wire terminal on the start capacitor's second wire onto the run capacitor's common terminal, often labeled "C," "COM." The wire connected to the motor's run terminal, marked as "R" on the motor's wiring chart, and the wire going to the hot terminal on the load side of the contactor also connects to this run capacitor terminal.