Capacitors are a necessary part of most air conditioners and are used to store electricity similar to batteries. These small devices help provide the initial jolt of power needed to get an AC motor up and running. However, most people do not understand that there are different types of capacitors and how they differ from one another. There are three main types of capacitors that are used in most AC motors; Start, Run and Dual.
The starting capacitor is a non-polarized aluminium electrolytic capacitor with a solid electrolyte that helps supply the required amount of energy for a short period to start an AC motor. These types of capacitors are only designed for a momentary application and should not be used for any longer than necessary.
Run capacitors are a type of low loss polymer capacitor that is used continuously while the AC motor is in operation. They are rated between 3-70uF or microfarad and can be used in place of a starter capacitor. They are a critical component in ensuring that the magnetic field within the motor remains stable. It is also important that the voltage and capacitance of a replacement run capacitor matches the original. Just like a radio requires the proper battery size, an AC motor cannot function properly with a less efficient run capacitor.
A dual run capacitor combines two single run capacitors in one case to save space and money. These are typically labelled with C, F and H (HERM for Hermetically-sealed compressor) on the label and have three connecting terminals on each side. The terminal marked F is used for the fan motor while the terminal labeled H is used to connect to a hermetically-sealed compressor.