Air Conditioning
What Is Capacitor & Contactor?
Definition
The capacitor stores and releases the extra jolt of electricity an AC compressor and fan motor need to start spinning; the contactor is the electrically-controlled switch that turns the outdoor unit's power on and off each time the thermostat calls for cooling. Both are common failure points because they cycle every single time the system runs.
Why it matters for your home
A failed capacitor or contactor is one of the most common reasons an AC "hums but won't start" or won't turn on at all — and it's usually a same-visit, inexpensive repair rather than a sign the whole system is failing.
What to do about it
If your AC suddenly stops working with no warning, mention any humming sound (capacitor) or clicking-but-nothing-happens (contactor) to the technician when you call — it helps them bring the right part on the first visit.
Related terms
This definition is pending licensed-trade technical review. It's sourced from our own published service and guide content, not invented — but hasn't yet been signed off by a licensed HVAC reviewer.
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