Amperimetric Relay

It has normally open contacts. When the compressor motor is energized, the current passing through the relay coil creates a magnetic field that attracts the armature upwards, closing the contacts and energizing the motor starting coil. When the compressor motor reaches gear speed, the current decreases to the point where the magnetic field does not have the strength to keep the armature up. In this way, the armature descends by the force of gravity, opening the contacts and consequently disconnecting the motor starting coil.