As the refrigerant flows, it cools the evaporator and
driver's compartment. It is a continuous tube looped
therefore reduces pressure in the thermal bulb. This
back and forth through many cooling fins firmly attached
allows the valve to close and stop refrigerant from
to the tube. The evaporator dehumidifies the air by
flowing into the evaporator. By carefully metering the
passing an airstream over the cool fins. As this
amount of refrigerant with the expansion valve, the
happens, the moisture condenses on the fins and drips
evaporator cooling efficiency is increased greatly.
down to collect and exit under the vehicle. Dust and dirt
also are collected on the moist fins and drain with the
b. Expansion Tube. The expansion tube (B, fig.
moisture. The temperature of the evaporator must be
kept above 320F. Should the temperature fall below
37-4) provides the same functions as the expansion
320F, moisture condensing on the evaporator would
valve. A calibrated orifice is built into the expansion
freeze, preventing air from passing through the fins. A
tube. The tube retards the refrigerant flow through the
typical evaporator is shown in figure 37-5. There
orifice to provide the metered amount of refrigerant to
basically are three methods of regulating evaporator
the evaporator. The tube also has a fine screen built in
temperature; each is discussed below.
for additional filtration.
a. Thermostatic Switch. This system (fig. 37-6)
37-6. Evaporator. The evaporator is designed to
uses an electrically operated switch to
absorb heat from the airstream directed into the
Figure 37-5. Typical Evaporator