AIR CONDITIONING AND HEATING SYSTEM CONTINUED
In an expansion valve system, the evaporator coil (Figure 6, Item 1) receives liquid refrigerant from the expansion
valve. In an orifice tube system, the evaporator receives liquid refrigerant from the orifice tube assembly. The liquid
refrigerant that is received by the evaporator has low pressure and low temperature. Since the pressure of the
liquid refrigerant is low, the temperature of saturation of the refrigerant is low. At the temperature of saturation, the
refrigerant changes from a liquid into a vapor. The temperature of saturation of a fluid increases when the pressure
of a fluid increases.
The evaporator coil (Figure 6, Item 1) is exposed to the air that is inside of the cab. The heat from the air that is
inside of the cab is absorbed by the evaporator. The evaporator transfers the heat to the refrigerant. The amount of
heat that is required to reach the temperature of saturation is called the latent heat of vaporization. When this heat
is absorbed by the refrigerant, the temperature of the refrigerant will reach the temperature of saturation. The
refrigerant will change from a liquid into a vapor. The vaporized refrigerant will leave the evaporator. The vaporized
refrigerant will carry away the heat from the cab. The vaporized refrigerant will return to the compressor when the
refrigerant leaves the evaporator. This process is repeated continuously.
Figure 6. Evaporator Coil.