Expansion Tube

The expansion tube (view B, fig. 13-5) provides the same functions as the expansion valve. A calibrated orifice is built into the expansion tube. The tube retards the refrigerant flow through the orifice to provide the metered amount of refrigerant to the evaporator. The tube, also, has a fine screen built in for additional filtration.

THE EVAPORATOR

The evaporator is designed to absorb heat from the airstream directed into the driver's compartment. It is a continuous tube looped back and forth through many cooling fins firmly attached to the tube. The evaporator dehumidifies the air by passing an airstream over the cooling fins. As this happens, the moisture condenses on the fins and drips down to collect and exit under the vehicle. Also, dust and dirt are collected on the moist fins and are drained with the moisture. The temperature of the evaporator must be kept above 32°F. Should the temperature fall below 32°F, moisture condensing on the evaporator would freeze and prevent air from passing through the fins. A typical evaporator is shown in figure 13-6. There are basically three methods of regulating evaporator temperature; each is examined below.