OIL 7X7840 - Caterpillar

Illustration 1 g00883962
(1) Heater core (2) Evaporator coil (3) Temperature sensor (Defrost) (4) Water valve (5) Expansion valveEvaporator coil (2) in the air conditioning system is a heat exchanger that is cooled by air. The evaporator coil is located in the heating and air conditioning unit. A blower motor forces the surrounding air over the evaporator coil and over the heater core. If the operator wants hot air, the system switches off the compressor and the system closes the water valve (4). If the operator wants cold air, the system switches on the compressor and the system closes the water valve.The air gives up some latent heat to the refrigerant in the evaporator. As latent heat is given up by the air, the air temperature is lowered. The pressure of the refrigerant is lowered as the refrigerant passes through expansion valve (5). This lower pressure lowers the boiling point of the refrigerant. Latent heat is absorbed from the air, as the refrigerant flows through the evaporator coil. Due to the absorbed latent heat, the liquid refrigerant changes to a vapor. Fins on the evaporator coils increase the surface area. This increased surface area allows more heat transfer from the air to the refrigerant.The amount of refrigerant that flows through the evaporator is controlled by the expansion valve. The expansion valve regulates the amount of refrigerant that can flow through the evaporator. This allows only refrigerant vapor to exit the evaporator. The refrigerant in the evaporator is superheated in order to ensure that only vapor leaves the evaporator. Only refrigerant vapor leaves the evaporator due to the damaging effects of liquid refrigerant in the compressor.