A capacitor is a small cylindrical device that stores an electrical charge to provide the "jumpstart" needed to get motors and compressors running. Most residential systems use a "dual run" capacitor, which supports both the compressor and the outdoor fan motor simultaneously. Over time, heat and electrical surges can cause a capacitor to fail, which is one of the most common reasons a Mobile Home AC Condensers will stop cooling. If you hear a humming sound from your outdoor unit but the fan isn't spinning, the capacitor is likely the culprit. You can find high-quality replacement electrical components in our Parts collection. It is measured in microfarads (µF), and using the incorrect rating can lead to permanent motor damage. Because they store electricity even when the power is off, they must be handled with extreme caution by a professional. Keeping a spare on hand is a smart move for homeowners with Packaged Units.