Figure 37-5. Typical Evaporator

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Figure 37-4. Expansion Valve and Expansion Tube.

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TM-9-8000 Principles of Automotive Vehicles Manual

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Figure 37-6. Thermostatic Evaporator.

TM 9-8000

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

37-6