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, and usually a quick 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. You get the flat-rate price on site, before any work starts, and the visit is the $79 dispatch and diagnostic fee.
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
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