Air conditioning (Refrigerant system): Description and operation

In the heater assembly, the temperature of the air distributed to the vehicle interior can be adjusted by passing a proportion, or all, of the cooled air through the heater matrix. The volume of air being distributed is controlled by the variable speed blower in the heater assembly. For details of temperature control and distribution. See Heating & Ventilation, Description and Operation.

The air conditioning system comprises a refrigerant system, a cooling unit and a control system.

REFRIGERANT SYSTEM

The refrigerant system transfers heat from the vehicle interior to the outside atmosphere. 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 725 ± 25 g charge weight of R134a refrigerant as the heat transfer medium. ND oil 8 is added to the refrigerant to lubricate the internal components of the compressor (new compressors come pre filled with ND8 oil 8).

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 absorbtion 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

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 at the bottom right front of the engine. The drive pulley and refrigerant line connections differ between petrol and diesel engined models, but otherwise the compressor is the same on both engine variants. The compressor is a ten cylinder swash plate unit with a fixed displacement of 177.7 cc/rev. The auxiliary drive belt drives the compressor via a pulley and an electrically actuated magnetic 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 to₂ operate at 3430 kPa (497.5 lbf.in ) and vents excess pressure into the engine compartment.