Because starting a compressor requires more torque and draws at least three times the amperage of its normal running speed, compressor motors are equipped with a starting winding and a running winding and both compose the stator. At the instant of starting, current flows through both windings. When motor speed increases to about 75% of its normal running speed, a starting relay disconnects power to the starting winding, and the running winding continues operating the motor (see fig. 13). Since heavy wire is used in the starting winding, if it runs more than a few seconds, it will overheat and possibly burn.
A starting relay is an electrical device that energizes the starting winding for a brief time. The starting relay plays an important role in the life of a compressor motor. Should the relay not disengage from energizing the starting winding, the starting winding (in the compressor motor) will burn, and the compressor will have to be replaced. In household refrigeration units, they are installed under the compressor terminal cover and connected to the compressor start and run terminals. Some relays come with three openings that connect the starting relay to the three terminals of the compressor.
Many GE units are of this type. (See figs. 46 and 46a.)
