Air Conditioning - Component Locations Land Rover Range Rover L322

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Scheme 56

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

1. A refrigerant system
2. An air inlet housing
3. A heater assembly
4. Distribution ducts
5. Two forced ventilation outlets
6. An Automatic Temperature Control (ATC) ECU and sensors
7. An auxiliary coolant pump
8. A coolant valve.

The high line system incorporates the following additional components

1. A second coolant valve
2. A pollution sensor
3. A rear blower unit.

A Fuel Burning Heater (FBH) system is installed as standard on Td6 models and as an option on V8 models. The FBH is a supplementary heater installed in the heater coolant circuit. The FBH can be operated without the engine running to pre-heat the passenger compartment and after the engine starts to reduce the heater coolant warm-up time. On Td6 models, the FBH also boosts the heater coolant temperature while the engine is running at low ambient air and engine coolant temperatures, to maintain heater performance at an acceptable level.

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

1. A compressor
2. A condenser and receiver drier
3. A thermostatic expansion valve
4. An evaporator
5. 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.

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 vapor 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 vapor to liquid in the condenser.

Scheme 57

Compressor

The compressor circulates the 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.

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.

Scheme 58

Condenser

The condenser transfers heat from the refrigerant to the surrounding air to convert the vapor 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 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. 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 pack and the filter in the receiver drier module are serviceable items retained in position by a threaded plug.

Scheme 59

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 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.

Scheme 60

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.

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/odor filter, is installed in the air inlet housing to prevent odors and/or particulate matter from entering the vehicle with the fresh air.

Scheme 61

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 moldings. 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

1. A blower
2. A heater matrix
3. Control flaps
4. Control flap motors
5. The thermostatic expansion valve and the evaporator of the refrigerant system
6. The evaporator temperature sensor and either one (low line system) or two (high line system) heater matrix temperature sensors.

Scheme 62

Scheme 63

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). If the control voltage is less than 2 V the blower is off.

Scheme 64

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 separate 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.

Scheme 65

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.

Scheme 66

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.

Scheme 67

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, on the low and high line systems. 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. On the low line system a bus controlled stepper motor operates the distribution flaps cam mechanism. All of the stepper motors are controlled by the ATC ECU. None of the stepper motors are interchangeable.

Scheme 68

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 memorized 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 re-establish 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 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.

Scheme 69

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 variable 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 energized while the ignition is on.

Scheme 70

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

Scheme 71

1. The windscreen heater and windscreen wiper parking area heater (optional fit, not available on vehicles with infra red protection glass)
2. The windscreen washer jet heaters
3. The rear window heater
4. The front seat heaters.

The switches on the low line control panel have the following functions

Scheme 72

1. Windscreen Heater Switch: Enabled only with the engine running. Pressing the switch energizes the windscreen heater and the windscreen wiper parking area heater for a set time period, until the switch is pressed again or until the engine stops, whichever occurs first. A LED above the switch is illuminated while the heaters are on.
2. LH and RH Seat Heater Switches: Activates the heater elements in the seat cushion and seat back at one of two heat levels. The first press of the switch energizes the heater elements at the higher heat setting and illuminates two LED in the switch. A second press of the switch sets the heater elements to the lower heat setting and extinguishes one of the LED's. A further press of the switch de-energizes the heater elements and extinguishes the second LED. The seat heaters remain on until selected off or the ignition is switched off.
3. Temperature Switch: Adjusts the passenger compartment nominal temperature setting between 16 and 28 °C (60 and 84 °F). The temperature range is engraved on the switch surround (°F for NAS, °C for rest of world). A pointer on the switch indicates the selected temperature. In the minimum and maximum temperature positions, the temperature is set to maximum cooling or maximum heating respectively.
4. Blower Switch: For manual adjustment of blower speed. Up to seven LED's in the switch surround illuminate to indicate the selected blower speed.
5. Distribution Control Knob: For manual adjustment of air distribution. Includes AUTO setting where distribution flaps are set to a nominal comfort position.
6. A/C Switch: Activates the A/C compressor. Allows the A/C compressor to be selected off for economy operation. A LED above the switch is illuminated when the A/C compressor is selected on.
7. Recirculation Switch: For manual selection of fresh or recirculated air. A LED above the switch is illuminated when recirculated air is selected.
8. Rear Window Heater Switch: Enabled only with the engine running. Pressing the switch energizes the rear window heater for a set time period, until the switch is pressed again or until the engine stops, whichever occurs first. A LED above the switch is illuminated while the heater is on.

The switches on the high line control panel have the following functions

1. Windscreen Heater Switch: Energizes the windscreen heater and the windscreen wiper parking area heater for a set time period, until the switch is pressed again or until the engine stops, whichever occurs first. A LED above the switch is illuminated while the heaters are on.
2. LH and RH Seat Heater Switches: Activates the heater elements in the seat cushion and seat back at one of two heat levels. The first press of the switch energizes the heater elements at the higher heat setting and illuminates two LED in the switch. A second press of the switch sets the heater elements to the lower heat setting and extinguishes one of the LED's. A further press of the switch de-energizes the heater elements and extinguishes the second LED. The seat heaters remain on until selected off or the ignition is switched off.
3. LH and RH Temperature Switches: Adjusts the nominal temperature settings of the LH and RH sides of the passenger compartment between 16 and 28 °C (60 and 84 °F). The temperature range is engraved on the switch surrounds. A pointer on each switch indicates the selected temperature. In the minimum and maximum temperature positions, the system operates at maximum cooling or maximum heating respectively.
4. Automatic Mode Switch: Activates the automatic modes for air volume and distribution and also activates the compressor. Separate LED's in the automatic mode switch illuminate when the blower and the distribution control flaps are in automatic mode. Manually selecting the blower speed or a distribution switch extinguishes the related LED.
5. Blower Switch: For manual adjustment of blower speed. Up to seven LED's in the switch surround illuminate to indicate the selected blower speed.
6. A/C Switch: Controls activation of the A/C compressor. Allows the A/C compressor to be selected off for economy operation. A LED above the switch is illuminated when the A/C compressor is selected on.
7. Recirculation Switch: For manual or automatic selection of fresh or recirculated air. Two LED's above the switch illuminate to indicate the mode and position of the recirculation flaps. The first press of the switch sets the recirculation flaps to automatic mode and illuminates the LH LED. A second press of the switch manually sets the recirculation flaps to the recirculation position, extinguishes the LH LED and illuminates the RH LED. A further press of the switch manually sets the recirculation flaps to the fresh air position and extinguishes the RH LED.
8. Maximum A/C Switch: For selection of maximum A/C when the ignition is on or rest heating when the ignition is off. A LED above the switch is illuminated when maximum cooling or rest heating is selected.
9. Distribution Switches (Windscreen, Face and Footwell): For manual selection of air distribution in any combination of windscreen, face and footwell outlets. A LED above each switch illuminates when a selection is made.
10. Defrost Program Switch: Activates a program that automatically selects the windscreen heater on, activates the compressor and changes the system settings to direct dry heat to the windscreen. A LED above the switch is illuminated while the defrost program is active.
11. Rear Window Heater Switch: Enabled only with the engine running. Pressing the switch energizes the rear window heater for a set time period, until the switch is pressed again or until the engine stops, whichever occurs first. A LED above the switch is illuminated while the heater is on.

Inputs and Outputs

Five electrical connectors provide the interface between the ATC ECU and the vehicle/heater assembly wiring.

Both the low and high line systems receive ambient temperature, engine coolant temperature, engine speed and vehicle speed inputs in K bus messages from the instrument pack. If the K bus messages are missing or faulty, the ATC ECU adopts the following default values

1. Ambient temperature = 0 °C (32 °F)
2. Engine coolant temperature = 80 °C (176 °F)
3. Engine speed = 800 rev/min
4. Vehicle speed = zero.

If a fault develops in the input from the temperature selector switch on the control panel, the ATC ECU adopts a default value of 24 °C (75 °F).

ATC ECU Harness Connector C0249 Pin Details

ATC ECU Harness Connector C0249 Pin Details

ATC ECU Harness Connector C0923 Pin Details

ATC ECU Harness Connector C1629 Pin Details

ATC ECU Harness Connector C1630 Pin Details

ATC ECU Harness Connector C1630 Pin Details

ATC ECU Harness Connector C2295 Pin Details

ATC ECU Harness Connector C2295 Pin Details

Sensors

Both the low and the high line systems incorporate

1. An in-car temperature sensor
2. A refrigerant pressure sensor
3. An evaporator temperature sensor
4. A heater matrix temperature sensor.

The high line system also incorporates

1. A second heater matrix temperature sensor
2. A sunlight sensor
3. A pollution sensor.

In-car Temperature Sensor

The in-car temperature sensor is an encapsulated Negative Temperature Coefficient (NTC) thermistor that provides the ATC ECU with an input of passenger compartment air temperature. The in-car temperature sensor is installed behind a grille in the ATC ECU control panel. An electric fan in the ATC ECU runs continuously, while the ignition is on, to draw air through the grille and across the in-car temperature sensor.

The ATC ECU uses the signal from the in-car temperature sensor for control of the coolant temperature valve(s), blower speed and air distribution.

The signal voltage from the in-car temperature sensor is between 0 and 5 V. The ATC ECU monitors the signal voltage and defaults to a temperature of 20 °C (68 °F) if it goes out of the range 0.573 - 4.882 V

1. If the signal voltage is less than 0.573 V, the ATC ECU assumes there is a short circuit to ground
2. If the signal voltage is more than 4.882 V, the ATC ECU assumes there is an open circuit or a short circuit to battery.

Refrigerant Pressure Sensor

The refrigerant pressure sensor provides the ATC ECU with a pressure input from the high pressure side of the refrigerant system. The refrigerant pressure sensor is located in the refrigerant line between the condenser and the thermostatic expansion valve.

The ATC ECU supplies a 5 V reference voltage to the refrigerant pressure sensor and receives a return signal voltage, between 0 and 5 V, related to system pressure.

The ATC ECU uses the signal from the refrigerant pressure sensor to protect the system from extremes of pressure and to calculate compressor load on the engine for idle speed control. The ATC ECU also transfers the pressure value to the Engine Control Module (ECM), via the K bus, instrument pack and CAN bus, for use in controlling the speed of the engine cooling fan.

To protect the system from extremes of pressure, the ATC ECU disengages the compressor clutch if the pressure

1. Decreases to 1.9 +/- 0.2 bar (27.5 +/- 3 lbf/in 2 ): the ATC ECU engages the compressor clutch again when pressure increases to 2.8 +/- 0.2 bar (40.5 +/- 3 lbf/in 2 )
2. Increases to 33 +/- 1 bar (479 +/- 14.5 lbf/in 2 ): the ATC ECU engages the compressor clutch again when pressure decreases to 23.5 +/- 1 bar (341 +/- 14.5 lbf/in 2 ).

Evaporator Temperature Sensor

The evaporator temperature sensor is a NTC thermistor that provides the ATC ECU with a temperature signal from the air outlet side of the evaporator. The evaporator temperature sensor is installed in the RH side of the heater assembly casing, and extends into the core of the evaporator.

The ATC ECU uses the input from the evaporator temperature sensor to control the engagement and disengagement of the compressor clutch, to prevent the formation of ice on the evaporator.

The signal voltage from the evaporator temperature sensor is between 0 and 5 V. The ATC ECU monitors the signal voltage and defaults to a temperature of 0 °C (32 °F) if it goes out of the range 0.157 - 4.784 V

1. If the signal voltage is less than 0.157 V, the ATC ECU assumes there is a short circuit to ground
2. If the signal voltage is more than 4.784 V, the ATC ECU assumes there is an open circuit or a short circuit to battery.

Heater Matrix Temperature Sensor

The heater matrix temperature sensor is a NTC thermistor that provides the ATC ECU with a temperature signal from the air outlet side of the heater matrix. On low line systems, a single sensor is installed in the rear of the heater assembly casing, to the right of the centre-line. On high line systems, two sensors are installed, one each side of the centre-line.

The ATC ECU uses the input from the heater matrix temperature sensor(s) to control the operation of the coolant valve(s).

The signal voltage from each heater matrix temperature sensor is between 0 and 5 V. The ATC ECU monitors the signal voltage and defaults to a temperature of 55 °C (131 °F) if it goes out of the range 0.173 - 4.890 V

1. If the signal voltage is less than 0.173 V, the ATC ECU assumes there is a short circuit to ground
2. If the signal voltage is more than 4.890 V, the ATC ECU assumes there is an open circuit or a short circuit to battery.

Sunlight Sensor

The sunlight sensor consists of two photoelectric cells that provide the ATC ECU with inputs of light intensity, one as sensed coming from the left of the vehicle and one as sensed coming from the right. The inputs are a measure of the solar heating effect on vehicle occupants and used by the ATC ECU to adjust blower speed, temperature and distribution to improve comfort. The sensor is installed in the centre of the fascia upper surface.

If one of the photoelectric cells is faulty, the output from the other photoelectric cell is used for both sides of the vehicle. If both photoelectric cells are faulty, the ATC ECU uses a default value of zero.

Pollution Sensor

The pollution sensor allows the ATC ECU to monitor the ambient air for the level of hydrocarbons and oxidized gases such as nitrous oxides, sulphur oxides and carbon monoxide. The pollution sensor is installed at the rear of the radiator, on the upper RH side of the viscous fan housing.

The ATC ECU outputs a battery power supply to heat the pollution sensor to operating temperature, and a 5 V reference voltage for the signal. The signal voltage from the pollution sensor is between 0 and 5 V.

If there is a fault with the pollution sensor, the ATC ECU disables automatic closing of the recirculation flaps on detection of pollutants.

Auxiliary Coolant Pump

The auxiliary coolant pump is an electric pump that ensures there is a satisfactory flow rate through the heater matrix at low engine speeds. The auxiliary coolant pump is installed in the engine compartment, in a rubber mounting attached to the side of the LH suspension turret. Operation of the auxiliary coolant pump is controlled by a power supply from the ATC ECU.

Coolant Valve

The coolant valve controls the coolant flow to the heater matrix. A single coolant valve controls the coolant flow to both sides of the heater matrix on low line systems. On high line systems, separate coolant valves control the coolant flow to each side of the heater matrix. The coolant valves are installed in the engine compartment on a bracket attached to the side of the LH suspension turret.

Each coolant valve is a normally open solenoid valve controlled by a Pulse Width Modulated (PWM) signal from the ATC ECU. The ATC ECU changes the length of time the coolant valve is open each duty cycle between 0 second (valve closed) and 3.6 seconds (valve held open). On the high line system, the PWM signals to the two valves are phase offset by 1.8 seconds to reduce coolant flow fluctuations.

FBH System

The system consists of a FBH unit, a FBH fuel pump and a changeover valve. On vehicles with the remote operation feature, the system also includes a FBH receiver and a remote handset.

Fuel for the FBH system is taken from the vehicle fuel tank, through a line attached to the fuel tank's fuel pump unit, and supplied via the FBH fuel pump to the FBH unit. In the FBH unit, the fuel delivered by the FBH fuel pump is burned and the resultant heat output is used to heat the engine coolant. The changeover valve isolates the heater coolant circuit from the engine coolant circuit

An ECU integrated into the FBH unit controls the operation of the FBH unit and the FBH fuel pump. The ATC ECU controls the changeover valve. System operation is initiated by

1. The instrument pack, via the ATC ECU, using I and K bus messages, for parked heating selections made on the Multi Information Display (MID) or Multi-Function Display (MFD)
2. The remote handset, via the TV antenna, TV amplifier and the FBH receiver, using radio and hardwired signals, for instant activation of parked heating
3. The ATC ECU, using K bus messages, for additional heating while the engine is running.

FBH Fuel Pump

The FBH fuel pump regulates the fuel supply to the FBH unit. The FBH fuel pump is installed below the RH side of the fuel tank in a rubber mounting attached to the rear subframe. The pump is a self priming, solenoid operated plunger pump. The ECU in the FBH unit outputs a pulse width modulated signal to control the operation of the pump. When the pump is de-energized, it provides a positive shut-off of the fuel supply to the FBH unit.

Scheme 73

The solenoid coil of the FBH fuel pump is installed around a housing which contains a plunger and piston. The piston locates in a bush, and a spring is installed on the piston between the bush and the plunger. A filter insert and a fuel line connector are installed in the inlet end of the housing. A non return valve and a fuel line connector are installed in the fuel outlet end of the housing.

While the solenoid coil is de-energized, the spring holds the piston and plunger in the 'closed' position at the inlet end of the housing. An 'O' ring seal on the plunger provides a fuel tight seal between the plunger and the filter insert, preventing any flow through the pump. When the solenoid coil is energized, the piston and plunger move towards the outlet end of the housing, until the plunger contacts the bush; fuel is then drawn in through the inlet connection and filter. The initial movement of the piston also closes transverse drillings in the bush and isolates the pumping chamber at the outlet end of the housing. Subsequent movement of the piston then forces fuel from the pumping chamber through the non return valve and into the line to the FBH unit. When the solenoid de-energizes, the spring moves the piston and plunger back towards the closed position. As the piston and plunger move towards the closed position, fuel flows past the plunger and through the annular gaps and transverse holes in the bush to replenish the pumping chamber.

FBH Unit

The FBH unit is installed in the passenger side rear of the engine compartment, below the battery. It is connected in series with the coolant supply to the heater assembly. Two electrical connectors on the FBH unit connect it to the vehicle wiring.

Scheme 74

Scheme 75

The FBH unit consists of

1. A circulation pump
2. A combustion air fan
3. A burner housing
4. An ECU/heat exchanger
5. An air inlet hose
6. An exhaust pipe
7. An air inlet filter.

Circulation Pump: The circulation pump is installed at the coolant inlet to the FBH unit to assist the coolant flow through the FBH unit and the heater assembly. The pump runs continuously while the FBH unit is in standby or active operating modes. While the FBH unit is inactive, coolant flow is reliant on the engine coolant pump and the auxiliary coolant pump.

Combustion Air Fan: The combustion air fan regulates the flow of air into the unit to support combustion of the fuel supplied by the FBH pump and to purge and cool the FBH unit. A canister type filter is included in the air inlet supply line to prevent particulates entering and contaminating the FBH unit.

Burner Housing: The burner housing contains the burner insert and also incorporates connections for the exhaust pipe, the coolant inlet from the circulation pump and the coolant outlet to the heater assembly. The exhaust pipe directs exhaust combustion gases to atmosphere through a pipe below the FBH unit.

The burner insert incorporates the fuel combustion chamber, an evaporator and a glow plug/flame sensor. Fuel from the FBH fuel pump is supplied to the evaporator, where it evaporates and enters the combustion chamber to mix with air from the combustion air fan. The glow plug/flame sensor provides the ignition source of the fuel: air mixture and, once combustion is established, monitors the flame.

ECU/Heat Exchanger: The ECU controls and monitors operation of the FBH system. Ventilation of the ECU is provided by an internal flow of air from the combustion air fan. The heat exchanger transfers heat generated by combustion to the coolant. A sensor in the heat exchanger provides the ECU with an input of heat exchanger casing temperature, which the ECU relates to coolant temperature and uses to control system operation. The temperature settings in the ECU are calibrated to compensate for the difference between coolant temperature and the heat exchanger casing temperature detected by the sensor. Typically, as the coolant temperature increases, the coolant will be approximately 7 °C (12.6 °F) hotter than the temperature detected by the sensor; as the coolant temperature decreases, the coolant will be approximately 2 °C (3.6 °F) cooler than the temperature detected by the sensor.

Changeover Valve

The changeover valve is a normally open solenoid valve installed between the supply and return sides of the heater coolant circuit. The changeover valve is located in the engine compartment on the engine bulkhead. When de-energized, the changeover valve connects the heater coolant circuit to the engine coolant circuit. When energized, the changeover valve isolates the heater coolant circuit from the engine coolant circuit.

The changeover valve is controlled by a power feed from the ATC ECU.

FBH Receiver

The FBH receiver translates the FBH request radio signals, relayed from the antenna receiver, into a voltage output to the FBH unit. When a request for parked heating is received, the FBH receiver outputs a battery power feed to the FBH unit. When a request to switch off parked heating is received, the FBH receiver disconnects the power feed.

The FBH receiver has a permanent power feed from the vehicle battery and is connected to the antenna receiver by a coaxial cable.

Scheme 76

The FBH remote handset allows parked heating to be remotely controlled up to a minimum of 100 m (328 ft) from the vehicle. On and off buttons activate and de-activate parked heating, a red LED illuminates to indicate when parked heating is active and when the on/off signals have been received by the vehicle. The FBH remote handset is powered by two serviceable 1.5 V batteries located under a cover on the rear of the handset.

Scheme 77

Scheme 78

Scheme 79

Scheme 80

Scheme 81

Both the low and high line systems operate on the reheat principle. The air entering the heater assembly is cooled to a constant value by the evaporator and then reheated as necessary by the heater matrix to produce the temperature(s) selected on the control panel.

To determine the various system settings, the ATC ECU derives a reference value (called the Y factor) from

1. The temperature setting on the control panel
2. The ambient temperature
3. The in-car temperature.

The reference value is measured in %, where -27.5% means maximum cooling is required and 100% means maximum heating is required. On the high line system, separate reference values are produced for the LH and RH sides of the heater assembly.

On both the low and high line systems the reference value is used for temperature control. On the high line system the driver's side reference value is also used for flap positioning and blower speed calculations.

When the ignition is turned off the ATC ECU memorizes the system settings and resumes the same settings the next time the ignition is switched on.

Compressor Control

The compressor is engaged by pressing either the automatic mode switch, defrost switch, A/C switch or maximum A/C switch. To prevent a dip in engine speed when the engine is at idle, a time delay of approximately 0.5 second is built into the compressor engagement process. The time delay allows the ECM to increase throttle angle and fuelling in anticipation of the additional load on the engine when the compressor engages.

When it receives an input to engage the compressor, the ATC ECU sends a message to the ECM, via the K bus, instrument pack and CAN bus, to advise that it wants to engage the compressor. Provided there are no engine management problems, the ECM responds by increasing throttle angle and fuelling and sending a message granting the request to the ATC ECU over the CAN bus, instrument pack and K bus. When it receives the grant message, the ATC ECU energizes the compressor clutch provided the following conditions exist

1. Engine speed is more than 400 rev/min
2. Evaporator temperature is more than 3 °C (37 °F)
3. The refrigerant pressure is within limits
4. Battery voltage is less than 16 V
5. The blower is running
6. There are no faults detected by the ATC ECU.

The compressor remains engaged until selected off or the required conditions no longer exist. If the evaporator temperature decreases to approximately 2 °C (36 °F) the compressor is disengaged, then re-engaged when the evaporator temperature increases to more than 3 °C (37 °F) again. If battery voltage exceeds 16 V for more than 5 seconds the compressor is disengaged, then re-engaged when voltage decreases to less than 15.8 V.

The compressor can also be disengaged by the ECM changing the grant message to a negative value or outputting a hardwired signal direct to the ATC ECU. Changing the grant message involves a time delay of up to 4 seconds before the ATC ECU de-energizes the compressor clutch. The time delay allows the ECM to decrease throttle angle and fuelling, in anticipation of the reduction in engine load when the compressor disengages, to prevent a sudden increase in engine speed if the engine is at idle. The hardwired signal is used to obtain instant disengagement of the compressor to ensure maximum acceleration when accelerator pedal demand suddenly goes from no load to full load. When this occurs the ECM sends a 12 V signal on a hardwired connection direct to the ATC ECU. When it receives the signal the ATC ECU immediately de-energizes the compressor clutch.

Engine Idle Speed Control

The ATC ECU signals the ECM to increase engine idle speed settings if a high current application is switched on or if low battery voltage is detected. The signal consists of a message transmitted via the K bus, instrument pack and CAN bus, and increases idle speed between 100 and 200 rev/min. The ATC ECU requests the engine idle speed increase when the following high current applications are switched on

1. Rear window heater
2. Blower, at speed 6 or 7
3. Headlamp main beam.

The engine idle speed increase is also requested if battery voltage decreases to less than 11.4 V. The speed increase request is discontinued when battery voltage increases to more than 12.2 V again.

Engine Cooling Fan Control

The engine's electric cooling fan is controlled by the ECM. When the compressor is engaged the ATC ECU sends a fan speed message between 0 (off) and 15 (maximum speed) to the ECM, via the K bus, instrument pack and CAN bus. The ATC ECU requests the cooling fan on when

1. The vehicle speed is less than 44 mph (70 km/h)
2. There is no fault with the compressor clutch circuit
3. Battery voltage is less than 16 V.

The fan speed requested depends on the pressure in the refrigerant system. The higher the pressure the faster the fan speed that is requested. When vehicle speed increases to more than 50 mph (80 km/h) the ATC ECU changes the fan speed request to 0 until vehicle speed decreases to less than 44 mph (70 km/h) again.

If battery voltage increases to more than 16 V for 5 seconds the ATC ECU changes the fan speed to 0 until the voltage decreases to less than 15.8 V.

Temperature Control

To determine the amount of heat required, in the form of coolant flow through the heater, the ATC ECU compares the reference value with the heater matrix temperature and incorporates a correction factor to compensate for changes of coolant flow rate with engine speed. From the resultant value the ATC ECU determines the open duration of the coolant valve and outputs the appropriate control signal. On the high line system, separate values and output signals are generated for each coolant valve to produce the individual temperature control for the LH and RH sides of the passenger compartment.

When the temperature setting on the control panel is set to maximum, the ATC ECU signals the coolant valve to remain open. When the temperature setting on the control panel is set to minimum, the ATC ECU signals the coolant valve to remain closed.

On the high line system, the minimum setting is over-ridden when the defrost program, maximum A/C, rest heating or FBH functions are selected.

Scheme 82

Flap Control - Low Line System

While the ignition is on, the position of the recirculation flaps is manually controlled by selection of the recirculation switch on the control panel and the steering wheel switch. If the recirculation flaps are in the recirculation position when the ignition is switched off, the ATC ECU automatically sets them to the fresh air position, to ensure that fresh air is available if a fault occurs with the recirculation flap drive circuit at the next ignition on.

The positions of the distribution flaps are manually controlled by selection of the distribution rotary switch on the control panel. The flaps are also automatically positioned by the ATC ECU to open the

1. Windscreen and footwell outlets, when parked heating is initiated by the FBH
2. Face and footwell outlets, when parked ventilation is initiated
3. Windscreen outlets, when the ignition is switched off and the ambient temperature is less than 0 °C, or windscreen and footwell outlets when the ignition is switched off and the ambient temperature is 0 °C and above.

Flap Control - High Line System

The position of the ram air flaps is automatically controlled by the ATC ECU. The positions of the recirculation flaps and the distribution flaps are either automatically controlled by the ATC ECU or manually controlled by the related switches.

Ram Air Flaps

The ATC ECU progressively closes the ram air flaps, in four steps, as vehicle speed increases, and opens them again as vehicle speed decreases. At the maximum closed position, 90% of the fresh air inlet area is closed off. A hysteresis of 9 mph (15 km/h) prevents the ram air flaps from hunting at a constant vehicle speed.

Scheme 83

Recirculation Flaps

Unless the recirculation flaps are manually selected closed, using the recirculation switch on the control panel or the steering wheel switch, they are normally open, but automatically closed by the ATC ECU under certain conditions.

Rapid Cooling: For rapid cooling of the passenger compartment, when the A/C system is selected on, if the driver's side reference value is less than -20% and the ambient temperature is more than 6 °C (43 °F), the ATC ECU closes the recirculation flaps. The ATC ECU opens the recirculation flaps after 12 minutes (temperate climates) or 20 minutes (hot climates), if the driver's side reference value increases to more than -5% or if the ambient temperature decreases to 6 °C (43 °F).

Pollution: When the ATC ECU detects a high level of pollutants, it sets the recirculation flaps to the recirculation position for

1. 3 minutes if the A/C system is in the heating mode
2. 10 minutes if the A/C system is in the cooling mode.

After the recirculation time period, the ATC ECU returns the recirculation flaps to the fresh air position. After 1 minute, if the pollutants are still present, the ATC ECU repeats the recirculation cycle.

Ignition Off: If the recirculation flaps are in the recirculation position when the ignition is switched off, the ATC ECU automatically sets them to the fresh air position, to ensure that fresh air is available if a fault occurs with the recirculation flap drive circuit at the next ignition on. When the ignition is switched on, the ATC ECU sets the recirculation flaps to the position they were in at ignition off.

Distribution Flaps

When a manual distribution selection is made on the control panel, the ATC ECU moves the distribution flaps to preset positions. When the system is in the automatic mode, the ATC ECU uses maps of the driver's side reference value to determine the position of the distribution flaps. Each distribution flap has a separate map, and there are separate maps for temperate and hot climates. The mapped positions of the face level distribution flaps are given a correction factor from the sunlight sensor inputs. The mapped positions of the distribution flaps are overridden by special programs, as follows

Condensation Prevention: To prevent condensation on the windscreen, the ATC ECU closes the windscreen flaps for 12 seconds each time the engine starts. If a manual distribution selection is made during the 12 seconds, the windscreen flaps revert to normal control.

The ATC ECU also closes the windscreen flaps when the reference value is less than 90% with the recirculation flaps closed and the compressor is disengaged.

Cold Start: When the engine starts, if the system is in the automatic mode, the driver's side reference value is 100% and the heater matrix temperatures is less than 30 °C (86 °F), the ATC ECU closes the face level and footwell flaps and opens the windscreen flaps.

Duct Purging: After a cold start, if the system is in the automatic mode and the reference value is 100%, the ATC ECU keeps the face level flaps closed until one of the heater matrix temperatures exceeds 60 °C (140 °F). The ATC ECU then fully opens the face level flaps for 25 seconds to purge the ducts of cold air. After the purge the face level flaps revert to normal automatic control. If, before or during the purge process, the reference value decreases below 100%, the ignition has been on for 15 minutes, or a manual distribution selection is made, then the purge process is cancelled.

Blower Control

In the automatic mode, blower speed is determined from reference temperature maps. In general terms, the more heating or cooling required to achieve the temperature selected on the control panel with the driver's side temperature switch, the faster the blower speed.

When maximum cooling is first required in the automatic mode, the ATC ECU runs the blower at full speed for a fixed period regardless of any drop in passenger compartment temperature. Different time periods are incorporated for the following markets

1. NAS and Gulf States
2. Europe and ROW
3. Japan.

NAS and Gulf States have the longest time period with the blower at full speed and Japan the shortest. T4 can be used to change the market setting so, in some cases, if a customer complains of the duration the blower runs at full speed, changing the market setting could resolve the complaint.

When heating is required, blower speed is reduced if the engine is cold and then progressively increased to the nominal setting as the engine coolant temperature increases from 20 to 50 °C (68 to 122 °F).

On the high line system, blower speed is also influenced by the sunlight sensor. At high light levels blower speed will increase to increase the cooling effect.

When the blower is selected off temperature regulation is no longer possible so the ATC ECU disengages the compressor, de-energizes the auxiliary water pump and closes the coolant valves. Pressing any of the A/C system switches restores blower operation and activates the required function. If the blower is selected off when the ignition is switched off, the blower remains off if the ignition is switched on again within 15 minutes. If more than 15 minutes elapses between the ignition being switched off and back on again, the ATC ECU switches the blower on at speed 1.

If battery voltage is low the ATC ECU reduces blower speed to conserve power. If battery voltage decreases to less than 12 V, the ATC ECU decreases the blower signal voltage, and thus the voltage to the blower motor, in direct proportion to the reduction in battery voltage.

Defrost Program (High Line System Only)

When the defrost program is selected the ATC ECU

1. Opens the windscreen distribution flaps and closes the face and footwell flaps
2. Sets the recirculation flaps to the fresh air position
3. Runs the blower at speed 7
4. Activates the A/C compressor
5. Activates the rear window heater
6. Activates the windscreen heater (where fitted).

When the ambient temperature is 10 °C (50 °F) and below, the ATC ECU signals the coolant valves to remain open. When the ambient temperature is more than 10 °C (50 °F), the ATC ECU checks the existing heater matrix temperature and, if necessary, increases the open time of the coolant valves to produce a minimum heater matrix temperature of 30 °C (86 °F).

The defrost program is cancelled by pressing the defrost switch again, or pressing the automatic, A/C or maximum A/C switches

Maximum AC (High Line System Only)

Pressing the maximum A/C switch while the engine is running and the ambient temperature is more than 7 °C (45 °F) provides the maximum cooling possible from the system to cool the passenger compartment down as rapidly as possible. When maximum A/C is selected the coolant valves are held closed, the A/C compressor is engaged, the blower speed is set to maximum and the recirculation flaps are set to the recirculation position. After 12 minutes the recirculation flaps will be set to fresh air for 1 minute then returned to the recirculation position.

The maximum A/C function is cancelled when any of the other A/C system switches are pressed.

Rest Heating (High Line System Only)

When the engine is not running, pressing the maximum A/C switch activates the rest heating function to heat the passenger compartment with residual heat from the engine. The rest heating function activates provided the following conditions exist

1. It is less than 15 minutes since the ignition was selected off
2. Ambient temperature is less than 15 °C (59 °F)
3. On the previous ignition cycle engine temperature exceeded 70 °C (158 °F)
4. Battery voltage is 11.4 V minimum.

To provide the rest heating function, the ATC ECU activates the auxiliary coolant pump, coolant valves, control flap and blower. The ATC ECU regulates the temperature (to the driver setting selected before the ignition was switched off), opens the face level distribution flaps and runs the blower at speed 4.

The rest heating function is cancelled after 15 minutes or when

1. The maximum A/C switch is pressed again
2. The ignition is selected on
3. Battery voltage decreases to less than 11 V.

Rear Passenger Face Level Air (High Line System Only)

The volume and temperature of the air from the rear passenger face vent are adjusted with the thumbwheels at the sides of the vent assembly. Each thumbwheel operates a variable potentiometer connected to the ATC ECU. The volume thumbwheel controls stepless changes of rear blower speed between off and full speed. The temperature thumbwheel controls the position of the rear passenger face level blend flap in the heater assembly when the driver's side reference temperature is more than 0%.

Volume Control: The volume potentiometer outputs between 0 and 5 V to the ATC ECU. The ATC ECU translates the voltage from the potentiometer into a signal voltage for the output stage in the rear blower. Potentiometer voltages of less than 1.25 V are interpreted as a blower off selection and translate into a signal voltages less than 0.1 V. Potentiometer voltages between 1.25 and 5 V are translated into proportional signal voltages between 0.1 and 5 V.

The ATC ECU automatically switches off the rear blower when

1. The defrost program is active
2. The main blower is selected off
3. The engine cranks
4. The ignition is selected off (the rear blower remains off during rest heating, parked heating and parked ventilation).

Temperature Control: The temperature potentiometer outputs between 0 and 5 V to the ATC ECU. The ATC ECU translates the voltage from the potentiometer into a blend flap position between 0% (cold) and 100% (hot) and outputs the appropriate control signal on the M bus to the blend flap motor. Potentiometer voltages of less than 1.5 V translate to a blend flap position of 0%. Potentiometer voltages of more than 3.4 V translate to a blend flap position of 100%. Potentiometer voltages between 1.5 and 3.4 V translate linearly to blend flap positions between 0 and 100%.

Windscreen Heater (Where Fitted)

When the engine is running and the windscreen heater is selected on, the ATC ECU illuminates the LED above the switch and energizes the heated front screen relay attached to the passenger end of the fascia cross tube. If not already active, the ATC ECU also activates the A/C compressor and the blower, and sets air distribution to windscreen. After 10 minutes (when ambient temperature is -15 °C (5 °F) or above) or 17 minutes (when ambient temperature is less than -15 °C (5 °F)), the ATC ECU extinguishes the LED and de-energizes the heated front screen relay. After the heater times out or is switched off, the timer in the ATC ECU is reset to zero.

Rear Window Heater

When the engine is running and the rear window heater is selected on, the ATC ECU illuminates the LED above the switch and energizes the rear window heater relay on the rear fusebox. After 10 minutes (when ambient temperature is -15 °C (5 °F) or above) or 17 minutes (when ambient temperature is less than -15 °C (5 °F)), the ATC ECU extinguishes the LED and operates the rear window heater at low power for 60 minutes. During the 60 minutes, the ATC ECU cycles the rear window heater relay off for 80 seconds and on for 40 seconds. If the rear window heater switch is pressed again during the low power phase, the ATC ECU illuminates the LED again and returns the rear window heater to full power by keeping the rear window heater relay energized for 5 minutes. At the end of the 5 minutes the LED is extinguished and the 60 minutes low power phase is repeated.

The ATC ECU outputs a K bus message when the rear window heater is active. The message allows the navigation computer to compensate for the effect of the magnetic field generated when the rear window heater is active. The BCU transfers the message onto the P bus for the door modules, which activate the door mirror heaters together with the rear window heater.

Washer Jet Heaters

The ATC ECU automatically energizes the washer jets relay, on the passenger compartment fusebox, when the ignition is on and the ambient temperature is less than 3 °C (37 °F). If the ambient temperature increases to more than 6 °C (43 °F), the ATC ECU de-energizes the washer jets relay.

Parked Ventilation

Parked ventilation allows the vehicle interior to be ventilated with ambient air while parked with the engine stopped. Vehicles without a FBH have parked ventilation only. On vehicles with a FBH, parked ventilation operates in conjunction with parked heating ( see PARKED HEATING/VENTILATION below).

Parked ventilation is controlled by direct selection on the MID/MFD, or by using the MID/MFD to program one or two on/off cycle times in the following 24 hour period. Both the direct selection and programmed time modes of operation are selected when the engine is stopped and the ignition switch is in position I; if required, the key can then be removed from the ignition switch and the vehicle locked. Parked ventilation only operates if the ambient temperature is 16 °C (61 °F) or more, and is automatically de-activated after 30 minutes, regardless of any programmed 'off' time, to prevent excessive drain on the battery. Parked ventilation is automatically de-activated when the ignition is switched on.

When programmed times for parked ventilation are entered on the MID/MFD, the times are stored in the memory of the instrument pack and the red LED at the RH side of the MID/MFD is permanently illuminated.

At a programmed parked ventilation start time, or when parked ventilation is selected on using the MID/MFD, the instrument pack outputs

1. A parked ventilation request to the MID/MFD on the I bus
2. A parked ventilation request to the ATC ECU on the K bus
3. The ambient temperature to the ATC ECU and BCU on the K bus.

On receipt of the messages

1. The red LED on the MID/MFD flashes at 2 Hz, to indicate that parked ventilation is active
2. If the ambient temperature is 16 °C (61 °F) or more, the ATC ECU operates the blower at speed 1, opens the face level distribution flaps in the heater assembly and closes the windscreen and footwell flaps.

The ATC ECU disables parked ventilation if battery voltage is less than 11.4 V.

The FBH system operates in two modes

1. Parked heating, to heat the passenger compartment while the vehicle is parked with the engine off
2. Additional heating, to boost heater performance while the engine is running.

The ATC ECU disables FBH operation if battery voltage is too low.

1. When the engine is off the low voltage limit is 11.4 V for more than 10 seconds; the system is re-enabled if battery voltage increases to 12.2 V
2. When the engine is running the low voltage limit varies with ambient temperature, from 11.1 V at -25 °C (-13 °F) and below to 11.7 V at 15 °C (59 °F) and above; if battery voltage is below the limit for 2 minutes the system is disabled for the remainder of the ignition cycle.

During FBH operation, with or without the engine running, the coolant valves remain de-energized and heater matrix temperature is directly related to the temperature of the coolant coming from the FBH unit.

Parked Heating Ventilation

Parked heating works in conjunction with parked ventilation. When parked heating/ventilation is selected, the vehicle interior is either heated by parked heating or cooled by parked ventilation, depending on the ambient temperature. Parked heating occurs if the ambient temperature is less than 16 °C (61 °F); parked ventilation occurs if the ambient temperature is 16 °C (61 °F) or more.

Parked heating/ventilation is controlled by direct selection on the MID/MFD, by using the MID/MFD to program one or two on/off cycle times in the following 24 hour period, or by using the FBH remote handset. The direct selection and programmed time modes of operation are selected when the engine is stopped and the ignition switch is in position I. If required the key can then be removed from the ignition switch and the vehicle locked. In all operating modes, parked heating/ventilation is automatically de-activated after 30 minutes to prevent excessive drain on the battery. Parked ventilation is automatically de-activated when the ignition is switched on.

When programmed times for parked heating/ventilation are entered on the MID/MFD, the times are stored in the memory of the instrument pack and the red LED at the RH side of the MID/MFD is permanently illuminated.

If the engine is started while parked heating is on

1. If the engine coolant temperature is equal to or more than the heater coolant temperature, parked heating is switched off
2. If the engine coolant temperature is less than the heater coolant temperature, parked heating remains on until the engine coolant temperature reaches the heater coolant temperature.

Programmed and MID/MFD Selected Parked Heating/Ventilation

At a programmed parked heating/ventilation start time, or when parked heating/ventilation is selected on using the MID/MFD, the instrument pack outputs

1. A parked heating/ventilation request to the MID/MFD on the I bus
2. A parked heating/ventilation request to the ATC ECU and the Body Control Unit (BCU) on the K bus
3. Ambient and engine temperatures to the ATC ECU and BCU on the K bus.

On receipt of the messages

1. The red LED on the MID/MFD panel flashes at 2 Hz to indicate that parked heating/ventilation is active
2. If the ambient temperature is less than 5 °C (41 °F), the BCU activates the door mirror heaters for 3 minutes
3. If parked heating is activated, the ATC ECU: Energizes the changeover valve Sends a K bus message to activate the FBH Operates the blower at speed 1 Opens the windscreen distribution flaps in the heater assembly and closes the face and footwell flaps.
4. If parked ventilation is activated, the ATC ECU: Operates the blower at speed 1 Opens the face level distribution flaps in the heater assembly and closes the windscreen and footwell flaps.

When parked heating/ventilation is selected off, or after 30 minutes has elapsed, the instrument pack sends parked heating/ventilation off messages on the I and K buses. On receipt of the messages

1. The MID/MFD switches off the LED
2. If parked heating is active, the ATC ECU: Sends a K bus message to de-activate the FBH Switches off the blower Returns the distribution flaps to the previous settings After 3 minutes, de-energizes the changeover valve.
3. If parked ventilation is active, the ATC ECU: Switches off the blower Returns the distribution flaps to the previous settings.

Remotely Selected Parked Heating/Ventilation

When parked heating/ventilation is selected on with the remote handset, the request is received by the FBH receiver via the TV antenna and TV receiver. The FBH receiver relays the request as a hardwired signal to the FBH ECU. On receipt of the request, the FBH ECU sends the request to the ATC ECU and the instrument pack on the K bus. Parked heating/ventilation then operates as detailed above.

Scheme 84

Additional Heating

On Td6 models, additional heating reduces the heater warm-up time and is also used to maintain heater performance throughout the drive cycle. On V8 models, additional heating is only used to reduce the heater warm-up time at the beginning of the drive cycle, and only occurs if parked heating is already active when the engine starts.

The ATC ECU activates the additional heating mode when the engine is running and the following conditions coexist

1. The ambient temperature is less than 8 °C (41 °F)
2. The engine coolant temperature is less than 75 °C (167 °F)
3. The heater coolant temperature is less than 70 °C (158 °F)
4. The reference temperature is 100%
5. The blower is on.

To activate the additional heating mode, the ATC ECU energizes the auxiliary coolant pump and sends K bus messages to the FBH unit to start/continue operation (the changeover valve remains de-energized).

The ATC ECU stops the FBH and de-energizes the auxiliary coolant pump when any of the following occur

1. The engine stops
2. The ambient temperature increases to more than 15 °C (46 °F)
3. The engine coolant temperature increases to more than 75 °C (167 °F)
4. The heater coolant temperature increases to more than 70 °C (158 °F)
5. The reference temperature decreases to less than 90%
6. The blower is selected off.

Once initiated by a message from the ATC ECU, FBH operation is controlled by the ECU in the FBH unit. The ECU controls the FBH unit at one of two heat output levels, 2.5 kW at part load combustion and 5 kW at full load combustion.

Start Sequence : At the beginning of the start sequence the ECU energizes the glow plug function of the glow plug/flame sensor, to preheat the combustion chamber, starts the combustion air fan at slow speed and energizes the coolant circulation pump. After approximately 30 seconds, the ECU energizes the FBH fuel pump at the starting sequence speed. The fuel delivered by the FBH fuel pump evaporates in the combustion chamber, mixes with air from the combustion air fan and is ignited by the glow plug/flame sensor. The ECU then progressively increases the speed of the FBH fuel pump and the combustion air fan. Once combustion is established the ECU switches the glow plug/flame sensor from the glow plug function to the flame sensing function to monitor combustion. From the beginning of the start sequence to stable combustion takes approximately 90 seconds for a start to part load combustion and 150 seconds for a start to full load combustion.

Coolant Temperature Control : When the ECU first enters the active mode, it initiates a start to full load combustion. Full load combustion continues until the heat exchanger casing temperature reaches 72 °C (162 °F), at this point the ECU decreases the speed of the FBH fuel pump and the combustion air fan to half speed, to produce part load combustion. The ECU maintains part load combustion while the heat exchanger casing temperature remains between 68 and 76 °C (154 and 169 °F). If the heat exchanger casing temperature decreases to 68 °C (154 °F), the ECU switches the system to full load combustion again. If the heat exchanger casing temperature increases to 76 °C (169 °F), the ECU enters a control idle phase of operation.

On entering the control idle phase, the ECU immediately switches the FBH fuel pump off, to stop combustion, and starts a timer for the combustion air fan. After a 2 minute cool down period, the ECU switches the combustion air fan off and then remains in the control idle phase while the heat exchanger casing temperature remains above 71 °C (160 °F). If the heat exchanger casing temperature decreases to 71 °C (160 °F), within 15 minutes of the ECU entering the control idle phase, the ECU initiates a start to part load combustion. If more than 15 minutes elapse before the heat exchanger casing temperature decreases to 71 °C (160 °F), the ECU initiates a start to full load combustion.

In order to limit the build up of carbon deposits on the glow plug/flame sensor, the ECU also enters the control idle phase if the continuous part and/or full load combustion time exceeds 72 minutes. After the cool down period, if the heat exchanger casing is still in the temperature range that requires additional heat, the ECU initiates an immediate restart to part or full load combustion as appropriate.

Shutdown: When the ATC ECU sends a K bus message to de-activate the FBH operation, the ECU de-energizes the FBH fuel pump to stop combustion, but continues operation of the combustion air fan and the circulation pump to cool down the FBH unit. The cool down time depends on the combustion load at the time the message is received.

Cool Down Times

Cool Down Times

Diagnostics: The ECU monitors the FBH system for faults. Any faults detected are stored in a volatile memory in the ECU, which can be interrogated by T4. A maximum of three faults and associated freeze frame data can be stored at any one time. If a further fault is detected, the oldest fault is overwritten by the new fault.

The ECU also incorporates an error lockout mode of operation that inhibits system operation to prevent serious faults from causing further damage to the system. In the error lockout mode, the ECU immediately stops the FBH fuel pump, and stops the combustion air fan and circulation pump after a cool down time of approximately 2 minutes. Error lockout occurs for start sequence failures and/or combustion flameouts, heat exchanger casing overheat and out of limit input voltage. The error lockout mode can be cleared using T4, or by disconnecting the battery power supply for a minimum of 10 seconds.

Start Failure/Flameout: If a start sequence fails to establish combustion, or a flameout occurs after combustion is established, the ECU immediately initiates another start sequence. The start failure or flameout is also recorded by an event timer in the ECU. The event timer is increased by one after each start failure or flameout, and decreased by one if a subsequent start is successful. If the event timer increases to three (over any number of drive cycles), the ECU enters the error lockout mode.

Heat Exchanger Casing Overheat: To protect the system from excessive temperatures, the ECU enters the error lockout mode if the heat exchanger casing temperature exceeds 105 °C (221 °F).

Out of Limit Voltage: The ECU enters the error lockout mode if the battery or alternator power input is less than 10.5 +/- 0.3V for more than 20 seconds, or more than 15.5 +/- 0.5V for more than 6 seconds.

See also:
• PARKED HEATING/VENTILATION