Air Conditioning
Air Conditioning
COMPONENT LOCATION - TdV8
COMPONENT LOCATION - 4.2L/4.4L
OVERVIEW
The A/C (air conditioning) system transfers heat from the vehicle interior to the outside atmosphere to provide the heater assembly with dehumidified cool air. 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 A/C (air conditioning) compressor.
To accomplish the transfer of heat, the refrigerant is circulated around the system, where it passes through 2 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 A/C (air conditioning) compressor; the refrigerant decreases in pressure and temperature at the thermostatic expansion valve, then changes state from liquid to vapor in the evaporator, to absorb heat. The high pressure/temperature regime is from the A/C (air conditioning) compressor, through the condenser and receiver drier to the thermostatic expansion valve; the refrigerant increases in pressure and temperature as it passes through the A/C (air conditioning) compressor, then releases heat and changes state from vapor to liquid in the condenser.
Some vehicles may be fitted with a 4 zone climate control system.
A/C COMPRESSOR
The A/C (air conditioning) compressor circulates refrigerant around the system by compressing low pressure, low temperature vapor from the evaporator and discharging the resultant high pressure, high temperature vapor to the condenser. Although similar in appearance, the A/C (air conditioning) compressor installed on TdV8 vehicles differs slightly to the one installed on 4.2L and 4.4L vehicles.
4.2L and 4.4L A/C Compressor
TdV8 A/C Compressor
The A/C (air conditioning) compressor fitted to both petrol and diesel vehicles is a variable displacement unit. The secondary accessory drive belt, driven by the engine crankshaft, drives the A/C (air conditioning) compressor via a pulley and an electromagnetic clutch. Operation of the clutch is controlled by a power feed from the ATC (automatic temperature control) module.
The A/C (air conditioning) compressor is a 7 cylinder swash plate unit with a minimum displacement of 5.5 cu.cm/rev (0.34 cu.in/rev) and maximum displacement of 163 cu.cm/rev (9.95 cu.in/rev). A control valve in the A/C (air conditioning) compressor automatically adjusts the displacement (i.e. flow of refrigerant), between the minimum and maximum values, to match the thermal load of the evaporator. By matching the refrigerant flow to the thermal load of the evaporator, the variable A/C (air conditioning) compressor maintains a relatively constant evaporator temperature of approximately 3 to 4 degrees C (37 to 39 degrees F).
To protect the refrigerant system from unacceptably high pressure, a pressure relief valve is installed in the outlet side of the A/C (air conditioning) compressor. The pressure relief valve is set to open at 3.5 to 4.1 MPa (508 to 595 lbf/sq.in) and vents excess pressure into the engine compartment. The pressure relief valve closes again when the pressure decreases to 3.01 MPa (437 lbf/sq.in).
The clutch of the A/C (air conditioning) compressor incorporates a thermal cut-off fuse, which disconnects the power feed from the ATC (automatic temperature control) module if the temperature increases to 182 ± 5 degrees C (360 ± 9 degrees F).
CONDENSER AND RECEIVER DRIER
Condenser and Receiver Drier - 4.2 and 4.4L
Condenser - TdV8
Receiver Drier - TdV8
The condenser transfers heat from the refrigerant to the surrounding air to convert the vapor from the A/C (air conditioning) compressor into a liquid. A receiver drier module, integrated onto the LH (left-hand) side of the condenser, incorporates a filter and a desiccant to remove solid impurities and moisture from the refrigerant. The receiver drier module also functions as a reservoir for liquid refrigerant, to accommodate changes of heat load at the evaporator.
The condenser is installed immediately in front of the radiator.
The condenser is classified as a sub-cooling condenser and consists of a fin and tube heat exchanger installed between two end tanks.
4.2L and 4.4L
Divisions in the end tanks separate the heat exchanger into a three pass upper (condenser) section and a single pass lower (sub-cooler) section, which are interconnected by the receiver drier module. The desiccant cluster and the filter in the receiver drier module are serviceable items retained in position by a threaded plug.
TdV8
Divisions in the end tanks separate the heat exchanger into a four pass upper (condenser) section and a two pass lower (sub-cooler) section. A connector block on the left end tank of the condenser provides connections for the high pressure lines from the A/C (air conditioning) compressor and the evaporator. Two pipes at the bottom of the right end tank of the condenser provide connections for the receiver drier.
THERMOSTATIC EXPANSION VALVE
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 temperature and pressure of the refrigerant leaving the evaporator act on the thermostatic expansion valve to control the volume of refrigerant flowing through the evaporator. The warmer the air flowing through the evaporator matrix, the more heat available to evaporate refrigerant and thus the greater the volume of refrigerant allowed through the metering valve.
EVAPORATOR
Evaporator and Thermostatic Expansion Valve
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 through the floorpan to the underside of the vehicle through two drain tubes.
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 near the front RH corner of the engine compartment.
CONTROL DIAGRAM
NOTE: A = Refrigerant liquid; B = Refrigerant vapor
