A capacitor is used in most HVAC systems, including furnaces. It has two main functions – it provides the additional torque needed for starting a unit and gives the unit the electricity needed to keep it running. They are on continuous duty while the motor is running.
Capacitors provide a steady supply of electricity to the fan motors and help the blowers move hot air through your system. In other words a capacitor is similar to a battery, storing electricity and stabilizing currents.
Without a capacitor your furnace’s motor will not start and the unit will not run. In fact, if the motor in your furnace won’t start, the capacitor is likely the problem.
Capacitors are categorized by microfarads and voltage. Microfarads are what measure the capacitors ability to store an electrical charge. A capacitor will range from 1.5 to 100 microfarads and will be classified at either 370 VAC or 440 VAC.