How do I test a capacitor?

Testing a residential HVAC capacitor requires a digital multimeter that features a microfarad (uF) measurement setting, along with strict adherence to electrical safety protocols. First, turn off all electrical power to the HVAC system at your main circuit breaker panel and outdoor disconnect box. Second, remove the service access panel and safely discharge the stored electrical energy inside the capacitor by placing an insulated screwdriver across the terminals to prevent severe shock. Third, disconnect all wires attached to the capacitor terminals. Fourth, set your digital multimeter to the microfarad scale and touch the meter probes across the appropriate terminals (such as Common to Fan and Common to Herm). You can verify the capacitor's condition by comparing the multimeter reading against the microfarad rating printed on the capacitor label; if the measured value is more than ten percent below the rated spec, the capacitor is bad.