The current start relays are used for motors with fractional power, which require a low starting torque. Its main function is to help start the engine. The start and run cables can be used together with the current relays to increase the starting and running torque.
Current relays are often observed when capillary tubes or fixed openings are used as measuring devices; The reason is that systems using capillary tubes and fixed holes as measuring devices will equalize the pressures during their stop cycle. This will cause a lower starting torque than systems that do not equalize the pressure during the stop cycle, as in the case of the conventional thermostatic expansion or the automatic expansion measuring device.
Some typical applications for current compressor relays could include household refrigerators, drinking fountains, air conditioners with small windows, smaller ice machines, and smaller supermarket display boxes.
The current start relays consist of a low resistance coil and a set of normally open contacts. The coil is connected between terminals L and M. The contacts are connected between terminals L and 2 when a start capacitor is used. If the backup capacitor is not in use, the contacts can be connected differently between terminals L and S. Terminals L, S and M are typical terminals for the identification of the current relays. L is the line, S is for the initial winding and M is for the main winding. This should help technicians connect a current relay to a compressor motor.
Note that when a start capacitor is used, terminals 2 and 3 can come into play. Also, when connecting capacitors to a motor that uses a current relay, always connect the start capacitor in series with the start coil. The operating capacitor will always be connected between the start and run terminals. Also keep in mind that different manufacturers may vary the names of the terminals to a certain extent.