AC Capacitor: Essential Guide for Replacement and Testing

An AC capacitor is a crucial component in many electrical devices, particularly in HVAC systems, air conditioners, and motors. It stores and releases electrical energy to help start and run motors efficiently. Over time, capacitors can fail due to wear, overheating, or power surges, leading to system malfunctions.

AC Capacitor for Air Conditioner Replacement

If your air conditioner is struggling to start, making humming noises, or shutting off unexpectedly, a faulty AC capacitor could be the culprit. Replacing it is a common repair that can restore your system’s efficiency.

Signs of a Bad AC Capacitor
Hard starting (motor struggles to turn on)
Humming sound but no cooling
Frequent system shutdowns
Visible bulging or leaking from the capacitor

Steps to Replace an AC Capacitor
Turn off power – Shut off the breaker to avoid electrical hazards.
Discharge the capacitor – Use an insulated screwdriver to short the terminals.
Take a photo of wiring – Ensures correct reconnection.
Remove the old capacitor – Note its microfarad (µF) rating and voltage.
Install the new capacitor – Match the terminals (C, HERM, FAN).
Restore power and test – Check if the AC starts smoothly.

Safety Tip: If unsure, consult an HVAC technician to avoid risks.

CBB60 water pump capacitor

How to Test an AC Capacitor with a Multimeter

A multimeter can help determine if your capacitor is working or needs replacement. Follow these steps:

Tools Needed
Digital multimeter (with capacitance setting)
Insulated screwdriver (for discharging)

Testing Steps
Disconnect & Discharge – Turn off power and discharge the capacitor.
Set Multimeter to Capacitance Mode (usually marked "CAP" or "–|(–").

Touch Probes to Terminals
For dual-run capacitors, test between C & HERM (compressor) and C & FAN.

Check the Reading
Good capacitor: Value should be within ±10% of the rated µF.
Bad capacitor: Significantly lower or no reading.

Example: If the capacitor is rated 35 µF, a reading between 31.5–38.5 µF is acceptable.

Alternative Method (Resistance Test)
If your multimeter lacks capacitance mode:

Set to Ohms (Ω).
Touch probes to terminals – A good capacitor will briefly show low resistance, then climb to infinity.