LR3/Disco 3
The thermostatic expansion valve meters the flow of refrigerant into the evaporator, to match the refrigerant flow with the
heat load of the air passing through the evaporator.
The thermostatic expansion valve is a block type valve located behind the heater assembly, and attached to the inlet and
outlet ports of the evaporator. The thermostatic expansion valve consists of an aluminum housing containing inlet and
outlet passages. A ball and spring metering valve is installed in the inlet passage and a temperature sensor is installed in
the outlet passage. The temperature sensor consists of a temperature sensitive tube connected to a diaphragm. The
bottom end of the temperature sensitive tube acts on the ball of the metering valve. Pressure on top of the diaphragm is
controlled by evaporator outlet temperature conducted through the temperature sensitive tube. The bottom of the
diaphragm senses evaporator outlet pressure.
Liquid refrigerant flows through the metering valve into the evaporator. The restriction across the metering valve reduces
the pressure and temperature of the refrigerant. The restriction also changes the liquid stream of refrigerant into a fine
spray, to improve the evaporation process. As the refrigerant passes through the evaporator, it absorbs heat from the air
flowing through the evaporator. The increase in temperature causes the refrigerant to vaporize and increase in pressure.
The temperature and pressure of the refrigerant leaving the evaporator act on the diaphragm and temperature sensitive
tube, which regulate the metering valve opening and so control the volume of refrigerant flowing through the evaporator.
The warmer the air flowing through the evaporator, the more heat available to evaporate refrigerant and thus the greater
the volume of refrigerant allowed through the metering valve.
EVAPORATOR
The evaporator is installed in the heater assembly between the blower and the heater matrix, to absorb heat from the
exterior or recirculated air. Low pressure, low temperature refrigerant changes from liquid to vapor in the evaporator,
absorbing large quantities of heat as it changes state.
Most of the moisture in the air passing through the evaporator condenses into water, which drains out of the heater and
Item Part Number
Description
1
-
Metering valve
2
-
Housing
3
-
Diaphragm
4
-
Temperature sensitive tube
5
-
Outlet passage from evaporator
6
-
Inlet passage to evaporator
