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 the Portland metro the failure often shows up when the system meets its first heavy load of a summer heat wave. Running on a weak capacitor makes the compressor strain at every start.
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 tune-up.
About this definition
Written by the Home Energy Group team — a family-owned HVAC company celebrating 25 years of comfort & care across SW Washington and the Portland metro, licensed in Washington (WA LIC# HOMEEGI003J7) and Oregon (OR CCB# 184255). Definitions inform; an on-site diagnosis decides.
