i) Defrost Heaters: The defrost heater is mounted onto or woven right into the evaporator coil in the freezer. The defrost termination limit switch is usually mounted on the side of the evaporator coil or on one of the connecting tubing. It is used for defrosting purpose.
ii) Thermostat: A thermostat is a component which senses the temperature of a refrigeration system so that the system's temperature is maintained near a desired set point. Usually it is fitted in evaporator for setting cooling temperature.
iii) Low Pressure or LP cut out: This is a compressor safety which cut off the compressor in the event of pressure drop in the suction line. The pressure of the suction line is continuously sensed by the control unit and when it goes below the set value, which means the room is properly cooled, the LP cut out will auto trip the compressor. When the pressure rises, indicating there is flow of refrigerant in the line due to increase in room temperature, the LP switch will start the compressor.
High pressure or HP cut out: As the name suggests, the high pressure cut out activates and trips the compressor when the discharge side pressure increases above the limit value. The HP cut out is not auto reset and has to be done manually. The reason behind it is to manually attend the fault which is leading to rise in pressure; else this situation can lead to overloading of compressor parts and may damage the same.