Discovery 2. Manual — part 710

AIR CONDITIONING

DESCRIPTION AND OPERATION

82-3

Description

General
The air conditioning system controls the temperature, distribution and volume of air supplied to the vehicle interior to
provide a comfortable cabin environment. The system is electronically controlled and features automatic and manual
modes of operation, with separate temperature control of the LH and RH air outlets. The automatic modes provide
optimum control of the system under most ambient conditions and require no manual intervention. The manual modes
allow individual functions of automatic operation to be overridden, to accommodate personal preferences.

The air conditioning system consists of a refrigerant system, a heater assembly and a control system. It also uses the
same air inlet duct and distribution ducts as the Heating and Ventilation system on non air conditioned vehicles.

+

HEATING AND VENTILATION, DESCRIPTION AND OPERATION, Description.

Fresh or recirculated inlet air flows into the heater assembly from the blower in the air inlet duct. In the heater
assembly, the air is cooled and/or heated, depending on the selected cabin temperature and ambient conditions, then
directed to selected air outlets.

On vehicles with rear air conditioning, additional cooling is provided by recirculating air through a second evaporator
and distributing it to outlets in the roof.

+

AIR CONDITIONING, DESCRIPTION AND OPERATION, Description.

AIR CONDITIONING

82-4

DESCRIPTION AND OPERATION

Refrigerant system

Schematic of air conditioning system

1 Evaporator
2 Thermostatic expansion valve
3 Low pressure servicing connection
4 Outlet to rear A/C system (where fitted)
5 Dual pressure switch
6 Receiver drier
7 Cooling fan
8 Condenser
9 Compressor

10 Inlet from rear A/C system (where fitted)
11 High pressure servicing connection
12 Air flows

a Ambient air

b Cooled air

c Ambient air through condenser

13 Refrigerant

a Liquid

b Vapour

The refrigerant system transfers heat from the vehicle interior to the outside atmosphere to provide the heater
assembly with dehumidified cool air. The system comprises a compressor, condenser, receiver drier, thermostatic
expansion valve and evaporator, joined together by refrigerant lines. The system is a sealed, closed loop, filled with
a charge weight of R134a refrigerant as the heat transfer medium. Oil is added to the refrigerant to lubricate the
internal components of the compressor.

AIR CONDITIONING

DESCRIPTION AND OPERATION

82-5

To accomplish the transfer of heat, the refrigerant is circulated around the system, where it passes through two
pressure/temperature regimes. In each of the pressure/temperature regimes, the refrigerant changes state, during
which process maximum heat absorption or release occurs. The low pressure/temperature regime is from the
thermostatic expansion valve, through the evaporator to the compressor; the refrigerant decreases in pressure and
temperature at the thermostatic expansion valve, then changes state from liquid to vapour in the evaporator, to absorb
heat. The high pressure/temperature regime is from the compressor, through the condenser and receiver drier to the
thermostatic expansion valve; the refrigerant increases in pressure and temperature as it passes through the
compressor, then releases heat and changes state from vapour to liquid in the condenser.

Compressor

1 Pulley
2 Inlet connection
3 Outlet connection
4 Pressure relief valve
5 Clutch connector

The compressor circulates the refrigerant around the system by compressing low pressure, low temperature vapour
from the evaporator and discharging the resultant high pressure, high temperature vapour to the condenser.

The compressor is attached to a mounting bracket on the engine, and is a ten cylinder swash plate unit with a fixed
displacement of 177 ml/rev (0.19 US qt/rev). The auxiliary drive belt drives the compressor via a pulley and an
electrically actuated clutch. Operation of the clutch is controlled by the Engine Control Module (ECM).

To protect the refrigerant system from unacceptably high pressure, a pressure relief valve is installed in the outlet side
of the compressor. The pressure relief valve is set to operate at 34.3 to 41.4 bars (497 to 600 lbf.in

2

) and vents excess

pressure into the engine compartment.

AIR CONDITIONING

82-6

DESCRIPTION AND OPERATION

Condenser

1 Condenser matrix
2 Outlet connection
3 Inlet connection

The condenser transfers heat from the refrigerant to the surrounding air.

The condenser is installed immediately in front of the oil coolers. Rubber mounting bushes are used to mount the
condenser to the chassis sidemembers and brackets on the headlamp panels.

Ambient air, passing through the condenser matrix due to ram effect and/or the cooling fan, absorbs heat from the
refrigerant, which changes state from a vapour to a liquid.