Discovery 2. Manual — part 711

AIR CONDITIONING

DESCRIPTION AND OPERATION

82-7

Receiver drier

1 Dual pressure switch
2 Inlet connection
3 Housing
4 Outlet connection
5 Outlet tube
6 Screen
7 Desiccant

The receiver drier removes moisture and solid impurities from the refrigerant and also acts as a refrigerant reservoir.

The receiver drier is clamped to a bracket in front of the condenser. The receiver drier housing is manufactured in
aluminium and contains a desiccant to absorb moisture. A mesh screen in the housing removes solid impurities. Inlet,
outlet and dual pressure switch connections are located in the top of the housing.

Liquid refrigerant enters the receiver drier, passes through the desiccant and mesh screen, and through a tube to the
outlet connection.

AIR CONDITIONING

82-8

DESCRIPTION AND OPERATION

Thermostatic expansion valve

Thermostatic expansion valve and evaporator

1 Refrigerant outlet
2 Refrigerant inlet
3 Thermostatic expansion valve
4 Evaporator

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 matrix.

The thermostatic expansion valve is installed in the heater assembly, in the refrigerant inlet line to the evaporator.
Liquid refrigerant flows through the valve to the evaporator. The restriction across the valve reduces the pressure and
temperature of the refrigerant and changes it to a fine spray, which improves the evaporation process. Valve opening
is controlled by the pressure in a capillary tube containing a temperature sensitive fluid. One end of the capillary tube
is connected to a diaphragm housing on the thermostatic expansion valve, the other end of the capillary tube is sealed
and attached to the refrigerant outlet line of the evaporator. As the temperature of the refrigerant leaving the
evaporator changes, a corresponding change of capillary tube pressure and valve opening are produced. The warmer
the refrigerant leaving the evaporator becomes, the greater the volume of refrigerant allowed through the valve.

AIR CONDITIONING

DESCRIPTION AND OPERATION

82-9

Evaporator
The evaporator is installed in the air inlet of the heater assembly and absorbs heat from the exterior or recirculated
inlet air. Low pressure, low temperature refrigerant changes from liquid to vapour in the evaporator, absorbing large
quantities of heat as it changes state.

Refrigerant lines
To maintain similar flow velocities around the system, the diameter of the refrigerant lines varies to suit the two
pressure/temperature regimes. The larger diameters are installed in the low pressure/temperature regime and the
smaller diameters are installed in the high pressure/temperature regime. Low and high pressure charging connections
are incorporated into the refrigerant lines for system servicing. Where rear AC is installed, connections for the rear
refrigerant lines are incorporated next to the charging connections.

AIR CONDITIONING

82-10

DESCRIPTION AND OPERATION

Heater assembly

1 Distribution servo motor
2 Refrigerant inlet and outlet connector block
3 RH blend flap servo motor
4 Thermostatic expansion valve
5 LH blend flap servo motor

The heater assembly controls the temperature and distribution of air supplied to the distribution ducts, and is similar
to the heater assembly installed in non A/C vehicles.

+

HEATING AND VENTILATION, DESCRIPTION AND OPERATION, Description. The only differences from

the heater assembly in non A/C vehicles are as follows:

l

The thermostatic expansion valve, evaporator and evaporator temperature sensor are installed at the air inlet
side of the casing.

l

Three servo motors operate the control flaps instead of control cables.

l

A coolant temperature sensor is installed against the heater matrix.

The servo motors are controlled by the ATC ECU. Feedback potentiometers in the servo motors provide the ATC ECU
with flap position signals.