What is the operation of a PTC type relay of a hermetic compressor?

The PTC relay consists basically of a ceramic insert that acts as a bridge between the relay contacts. This material has the property of increasing its resistance when heated by the current passing through it. During startup, with current flowing to the starter coil, the resistor rapidly reaches a very high value, reducing the current in the starter coil until it is withdrawn from operation. Its use is recommended for freezers and domestic refrigerators, due to the time required for cooling between the operating cycles.