Definition
A capacitor is an electrical component that stores and releases energy to start and run the motors in air conditioners, heat pumps and furnace blowers. A run capacitor keeps the compressor and fan motors turning efficiently, a start capacitor adds a brief boost at compressor startup, and a dual run capacitor serves the compressor and condenser fan together.
Also called: Run capacitor, Start capacitor, Dual run capacitor
Why it matters to you.
A failed capacitor is one of the most common reasons an outdoor unit hums but will not start, and in Central Kentucky the failure often surfaces on the first hot, humid stretch of summer when the system meets a heavy load. A heat pump's capacitor also works through the heating season, so it can fail in winter too.
Practical guidance.
A capacitor can hold a dangerous charge even with the power off, so never open the unit to test or replace one yourself. A licensed technician can measure it against its rated microfarads, typically as part of a spring cooling tune-up.
About this definition
Written by the Feistritzer Heating & Air Conditioning team — family owned and operated in Danville since 1976, Kentucky HVAC license M02584. Definitions inform; a whole-system diagnosis in your home decides.