Capacitors hold an electrical charge that is used to start a refrigerator motor when needed. A capacitor that doesn't work properly causes the appliance to stop cooling or could turn the motor on and off more frequently than normal.
Capacitors are sometimes called condensers. They can be rectangular or cylindrical and have at least two metal conducting wires attached. When the inside of the refrigerator rises above a certain temperature, the capacitor starts the compressor motor.
The compressor pushes the coolant into the condenser to bring the temperature back down. Then, the warmed coolant is sent to the evaporator to be cooled and sent back into the cycle. When the refrigerator reaches the correct temperature, the capacitor shuts the motor down.
Capacitors can be checked with an ohm meter to see if they work properly. The ohm meter individually tests the capacitor terminals, with the results showing on the device's screen. If the needle moves slightly, and then goes back to its starting position, the capacitor is fine.
Since capacitors hold large amounts of electricity and can discharge suddenly, this is a potentially dangerous test that should be done by professionals. It involves discharging the capacitor, and in some models, creating a short to avoid injury.