Heat pumps contain a run capacitor, which provides constant voltage to fans and other components, and start capacitors, which provide a boost of power when the compressor turns on. Start capacitors help improve start-up times for heat pumps.
Capacitors store and release energy on demand and are often described as similar to batteries. Unlike batteries, however, they store relatively little power and do not degrade as quickly.
Without a start capacitor, heat pumps would take far longer to start working. Compressors take a significant amount of energy to start, and capacitors speed up this process. Once the compressor is up to full speed, the capacitor disengages and charges up for when it is next needed.
Run capacitors are common on all HVAC systems that rely on fans to spread warm or cold throughout a structure. Fans rely on motors to operate, and motors need a consistent supply of electricity to operate at their optimal speed; capacitors ensure that the voltage received by the motor is consistent enough to provide efficient operation. They also protect against small dips and spikes in voltage, which can cause a fan motor or the fan itself to become damaged, helping to ensure the system's longevity.