What is AC Capacitor?
Plain-English explanation from a licensed Utah HVAC, plumbing, and electrical contractor.
An AC capacitor is a cylindrical electrical component that stores a charge to help start the compressor and fan motors of your air conditioner — when one fails the unit hums but won't start, or shuts off after a few minutes.
Full Definition
Air conditioner capacitors are passive electrical components rated in microfarads (μF) that store and release electrical energy in pulses. A start capacitor delivers a high-current kick to get the compressor motor spinning; a run capacitor provides a steady boost to keep the motor turning efficiently. Most residential AC condensers use a single dual-capacitor (e.g., 45/5 μF, 45/7.5 μF) that handles both the compressor and outdoor fan. Capacitors are sensitive to Utah's summer heat and typically last 8–12 years.
Failed capacitors are the #1 most common AC repair on the Wasatch Front — typical $189–$289 fix. Symptoms include: unit hums but won't start, fan runs but compressor doesn't, compressor starts then trips, or AC works for 10 minutes then quits. A swollen or leaking capacitor is dangerous and should be replaced same-day.
Common Questions
How do I know if my AC capacitor is bad?
Common signs: AC hums but won't start, fan spins but compressor doesn't engage, AC takes longer to start than normal, AC trips the breaker, or you see a swollen/leaking cylinder inside the condenser disconnect box. A multimeter capacitance test confirms it.
Can I replace an AC capacitor myself?
We don't recommend it — capacitors store dangerous high-voltage charge even after power is off. Improper handling causes serious shock or fire. The repair is fast for a licensed tech and includes safe discharge, correct μF matching, and testing the rest of the start circuit.
Related Terms
Contactor
An HVAC contactor is an electrically-controlled switch inside your outdoor AC unit — when the thermostat calls for cooling, low-voltage signal closes the contactor and sends 240V to the compressor and fan.
AC Compressor
The compressor is the heart of your air conditioner or heat pump — it's the pump that circulates refrigerant through the system, and replacement is by far the most expensive HVAC repair.
Refrigerant
Refrigerant is the working fluid inside an AC or heat pump — it absorbs heat indoors and releases it outdoors as it cycles between liquid and gas states.
Recent HVAC work in Utah
A few installs and service calls from the AYSP crew.
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