Compressor Capacitors

Start and Run Capacitors for Compressor Motors

Single-phase compressor motors may use one or more capacitors to create starting torque and maintain efficient operation. The correct capacitor must match the original motor specification and must not be selected from motor power alone.

Choose the Correct Capacitor

Start Capacitors and Run Capacitors Explained

Run Capacitors

A run capacitor remains connected while the motor operates. It helps maintain the phase relationship required for smooth running, efficient current draw and suitable motor performance.

Start Capacitors

A start capacitor provides a higher capacitance for a short period while the motor accelerates. It is normally disconnected by a centrifugal switch, relay or electronic starting device once the motor reaches operating speed.

Common Signs of Capacitor Failure

• The motor hums but does not start.
• The motor starts slowly or struggles under pressure.
• The overload trips repeatedly during starting.
• The capacitor casing is swollen, split or leaking.
• The motor starts only when manually assisted.
• The capacitor fails an appropriate capacitance test.

Installation and Safety Guidance

• Isolate the compressor from the electrical supply before inspection.
• Capacitors can retain a dangerous charge after power is removed.
• Record the original wiring before disconnecting terminals.
• Fit the correct start or run type with the specified µF and voltage rating.
• Secure the replacement so vibration cannot damage the case or terminals.
• Electrical testing and replacement should be completed by a competent person.