A run capacitor is an electrical component that stores and releases energy to keep the compressor and fan motors in an air conditioner or heat pump running efficiently. It is rated in microfarads (µF), and many outdoor units use one dual run capacitor serving both motors. A separate start capacitor, when fitted, gives the compressor a brief startup boost.
Why it matters to you
A weak capacitor is one of the most common reasons an air conditioner stops cooling on a hot afternoon, and it strains the compressor before it fails completely.
Practical guidance
A capacitor can hold a dangerous charge even with the power off, so testing and replacement belong to a pro. A bulging or leaking top is a visible warning sign, and a meter reading against the rated microfarads confirms it.