As is known, one of the electrical load on the refrigeration machine is deforst heater. Defrost heater is an electrical component in the refrigeration machine for controlling the amount of a layer of frost on the surface of the evaporator. When the layer of frost that accumulates on the surface of the evaporator is not removed it will interfere with the cooling process. Therefore, the refrigeration unit either for domestic or commercial purposes has been equipped with automatic defrost system, namely by using the defrost timer.
Defrost timer is one of the safety devices installed on the refrigerator unit. Figure 2.23 shows a typical defrost timer, which operates electromechanical. Figure 2.24 shows a typical defrost timer operating in microelectronics. Electronic control device is equipped with a microprocessor that can be programmed as needed.
System defrost (defrost) automatically applied to the refrigerator unit using a timer to activate the defrost cycle. In the automatic defrost system, added heater (pemenas elements) and the thermostat on the evaporator coil. Defrost timer set defrost cycle in the evaporator, typically every 8 hours. If during defrost arrived, then the compressor will stop working, and the defrost heater will be active. Defrost heater will heat the evaporator so that the frost melts.
Defrost thermostat will monitor the temperature of the evaporator, and when the evaporator temperature reaches a certain point, the defrost heater becomes inactive. Defrost thermostat commonly known as the defrost termination thermostat or defrost terminator or thermal defrost switch. The target evaporator temperature is typically 40 and 60 0F. 2:25 image shows the location of placement defrost termination and construction.
Water condensate tray accommodated by a type that is placed on the bottom of the evaporator where the heat from the compressor and condenser flowing through so as to accelerate the process of evaporation.
Some cycle defrost system implemented based on the time count. The amount of time chosen by the interval between defrost. If the timer counts the time that have been achieved, then the system will defrost start work, without taking into account the need for cooling in the system.
This configuration is commonly referred to as continuous run. Type of more effective computation time is a system that takes into account the amount of time the compressor work. When the timer detects the accumulation of compressor working time in accordance with the desired timing of the defrost system will work. Such systems are commonly referred to as a cumulative run-time defrost.