Description - 1
Description
General
Either a low or high line Air Conditioning (A/C) system is installed on the vehicle. The low line system features automatic control of a common temperature setting for both sides of the passenger compartment, with manual control of the blower speed, air recirculation and air distribution. The high line system is fully automatic with separate temperature settings for the LH and RH sides of the passenger compartment and manual overrides for blower speed, air recirculation and air distribution. The high line system also incorporates independent temperature and volume control for the rear passengers. The low and high line systems both include:
- A refrigerant system
- An air inlet housing
- A heater assembly
- Distribution ducts
- Two forced ventilation outlets
- An Automatic Temperature Control (ATC) ECU and sensors
- An auxiliary coolant pump
- A coolant valve
The high line system incorporates the following additional components:
- A second coolant valve
- A pollution sensor
- A rear blower unit
Refrigerant System
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
- A condenser and receiver drier
- A thermostatic expansion valve
- An evaporator
- 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.
Refrigerant System schematic
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 a fixed displacement unit attached to a mounting bracket on the engine. A dedicated drive belt on the engine crankshaft drives the compressor via a pulley and an electrically actuated clutch. Operation of the clutch is controlled by the ATC ECU.
Compressor Assembly
Condenser
The condenser transfers heat from the refrigerant to the surrounding air to convert the vapour from the compressor into a liquid. A receiver drier module integrated onto the LH side of the condenser, incorporates a filter and a desiccant to remove solid impurities and moisture from the refrigerant.
The condenser is installed immediately in front of the radiator.
Condenser Assembly
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
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 vapour 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.
Evaporator and Thermostatic Expansion Valve
Refrigerant Lines
To maintain similar flow velocities around the system the diameter of the refrigerant lines vanes 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.
Air Inlet Housing
The air inlet housing directs fresh air into the heater unit. The air inlet housing is centrally mounted on the engine bulkhead, below a ventilation grille in the bonnet, and secured to the bulkhead closing panels.
A serviceable particle filter or particle/odour filter, is installed in the air inlet housing to prevent odours and/or particulate matter from entering the vehicle with the fresh air.
Air inlet Housing
Heater Assembly
The heater assembly controls the temperature, volume and distribution of air supplied to the distribution ducts as directed by selections made on the ATC ECU control panel. The assembly is installed on the vehicle centre-line between the fascia and the engine bulkhead. The heater assembly consists of a casing formed from a series of plastic mouldings. Internal passages integrated into the casing guide the air through the casing and separate it into two flows, one for the LH outlets and one for the RH outlets. Two drain outlets at the bottom of the casing are connected to overboard drain hoses in the sides of the transmission tunnel.
The heater assembly incorporates:
- A blower
- A heater matrix
- Control flaps
- Control flap motors
- The thermostatic expansion valve and the evaporator of the refrigerant system
- The evaporator temperature sensor and either one (low line system) or two (high line system) heater matrix temperature sensors
Low Line Heater Assembly
High Line Heater Assembly
Blower
The blower is installed between the air inlets and the evaporator and consists of two open hub centrifugal fans powered by a single electric motor. Operation of the electric motor is controlled by the ATC ECU via an output stage (voltage amplifier) installed in the outlet of the RH fan.
To produce the seven blower speeds the ATC ECU outputs a stepped control voltage between 0 and 8 V to the output stage which regulates a battery power feed from the passenger compartment fusebox to the blower. The control voltage changes, in 1 V steps, between 2 V (blower speed 1) and 8 V (blower speed 7). It the control voltage is less than 2 V the blower is off.
Blower Output Stage
Heater matrix
The same heater matrix is used in both the low and high line heater assemblies. The heater matrix is internally divided into two separate halves with separately coolant inlets for each half and a common coolant outlet. On the low line system, the two coolant inlets are connected to a common feed from the single coolant valve. On the high line system each coolant inlet pipe is connected to a feed from a separate coolant valve.
Heater Matrix Assembly
Control Flaps
Control flaps in the heater assembly control the source of inlet air and the distribution and temperature of outlet air.
On both the low and high line heater assemblies, a fresh/recirculated air flap is installed in the air inlet on each side of the heater assembly. A stepper motor drives the LH fresh/recirculated air flap and a Bowden cable transmits the drive from the LH to the RH fresh/recirculated air flap. On the high line system, a ram air flap is installed inside each fresh/recirculated air flap. A stepper motor drives the RH ram air flap and a Bowden cable transmits the drive from the RH to the LH ram air flap.
Each side of the heater assembly contains separate distribution flaps for the footwell, face level and windscreen. The related flaps on each side of the heater assembly are installed on common drive spindles. On the low line heater assembly the distribution flaps are driven by Bowden cables connected to a cam mechanism, which in turn, is driven by a stepper motor. On the high line heater assembly, each set of distribution flaps is driven by a separate stepper motor.
On both the low and high line heater assemblies, a blend flap is installed below the face level outlets. The blend flap is driven by a Bowden cable connected to a thumbwheel on the centre face vents in the fascia, and allows the temperature of face level air to be modified with cold air direct from the evaporator.
Fascia Face Level Vent
On high line heater assemblies, a blend flap is installed for the rear passenger face level outlet to allow the temperature of rear face level air to be adjusted independently from the temperatures selected on the control panel. The blend flap is driven by a stepper motor controlled by a thumbwheel on the rear passenger face vent. The blend flap is also used to close off the rear face level outlet when maximum air output is required for the front outlets, e.g. when defrost is selected.
Rear Passenger Face Level Vent
Control Flap Motors
Two types of electrical stepper motor are used to operate the control flaps in the heater assembly. A conventional 500 Hz stepper motor operates the recirculation flaps and, on the low line System, the distribution flaps cam mechanism. On the high line system, five bus controlled 200 Hz stepper motors operate the ram air, distribution (windscreen, face level and footwell) and the rear face level temperature control flaps. All of the stepper motors are controlled by the ATC ECU. None of the stepper motors are interchangeable.
Typical Control Flap Motor
Each bus controlled stepper motor incorporates a microprocessor and is connected to an M bus from the ATC ECU, which consists of three wires making up power ground and signal circuits. The microprocessor in each bus controlled stepper motor is programmed with a different address. Each M bus message from the ATC ECU contains the address of an individual bus controlled stepper motor, so only that motor responds to the message.
None of the stepper motors incorporate a feedback potentiometer. Instead the ATC ECU determines the positions of the flaps by using either their closed or open position as a datum and memorizing the steps that it drives the individual stepper motors. Each time the ignition is switched on, the ATC ECU checks the memorised position of the stepper motors against fixed values for the current system configuration. If there is an error (e.g. after a power supply failure during operation or after replacement of the ATC ECU) the ATC ECU calibrates the applicable stepper motors, to reestablish the datums, by driving them fully closed or open before re-setting them to their nominal position. A calibration run can also be invoked using TestBook/T4.
When any of the control flaps are set to fully closed or open the ATC ECU signals the related stepper motor to move the appropriate number of steps in the applicable direction. To accommodate build tolerances and wear, and to ensure the flaps are held in the selected position every 20 seconds the ATC ECU signals the stepper motor to move an additional 10 steps in the relevant direction.
Distribution Ducts
Air from the heater assembly is distributed around the vehicle interior through distribution ducts to outlets in the fascia, the front and rear footwells, and the rear of the cubby box between the front seats.
In the fascia, the distribution ducts are connected to fixed vents for the windscreen and side windows and adjustable vent assemblies for face level air. An adjustable vent assembly is also installed on the rear of the cubby box for rear face level air. The footwell outlets are fixed vents formed in the end of the related distribution ducts.
Air Distribution
Forced Ventilation Outlets
The forced ventilation outlets promote the free flow of air through the passenger compartment. The outlets are installed in the LH and RH rear quarter body panels and vent passenger compartment air into the sheltered area between the rear quarter body panels and the rear bumper.
Rear Blower (High Line System Only)
The blower is installed between the front seats, in the rear face air duct, and consists of an open hub, centrifugal fan powered by an electric motor. Operation of the electric motor is controlled by a thumbwheel on the rear passenger face vent via the ATC ECU and an output stage (voltage amplifier) installed in the outlet of the fan.
The thumbwheel operates a vanable potentiometer which outputs between 1.25 V (blower off) and 5 V (maximum blower speed) to the ATC ECU. The ATC ECU then outputs a proportional control voltage between 0 and 5 V to the output stage, which regulates a battery power feed from the rear blower relay to the blower to produce the related blower speed.
The rear blower relay is installed in the rear fusebox and energised while the ignition is on.
Rear Blower Output Stage
ATC ECU
The ATC ECU is installed in the centre of the fascia. An integral control panel contains push switches and rotary switches/knobs for system control inputs. Orange tell-tale LED's in the switches and switch surrounds illuminate to indicate the current settings of the system. The rotary temperature switch is graduated in degrees Celsius, except on USA vehicles, where it is graduated in degrees Fahrenheit.
An in-car temperature sensor and associated electric fan are installed behind a grille in the control panel.
The ATC ECU processes inputs from the control panel switches and system sensors, then outputs the appropriate signals to control the A/C system. In addition to controlling the A/C system the ATC ECU also controls the following:
- The windscreen heater and windscreen wiper parking area heater (optional fit, not available on vehicles with infra red protection glass)
- The windscreen washer jet heaters
- The rear window heater
- The front seat heaters
Low Line Control Panel
