Climate Control: Overview Jaguar XJ X351

OVERVIEW

The heating and ventilation system controls the temperature and flow of air supplied to the passenger compartment. The system is either a dual zone or four zone system, depending on vehicle specification.

SYSTEM OPERATION

PRINCIPLES OF OPERATION

Operation of the heating and ventilation system is controlled by the automatic temperature control (ATC) module. Refer to Control Components .

The system can be operated in automatic or manual mode, with temperature settings selected using the switches on the integrated control panel and, on four zone systems, the rear climate control panel.

When the engine is running, coolant is constantly circulated through the heater core by the engine coolant pump.

The blower is supplied with power from the blower relay on the rear junction box (RJB) and connected to ground via the blower control module. The blower control module regulates the voltage across the blower motor to control blower speed. The voltage set by the blower control module is controlled by a pulse width modulation (PWM) signal from the automatic temperature control (ATC) module. The automatic temperature control (ATC) module uses a feedback signal from the blower control module to monitor blower speed.

COMPONENT DESCRIPTIONS

HEATER ASSEMBLY

Scheme 1

The heater assembly controls the temperature and flow of air supplied to the air distribution ducts. The heater assembly is mounted on the vehicle centerline, between the instrument panel and the engine bulkhead. The heater assemblies on two and four zones systems are the same.

The heater assembly consists of a casing that contains an air conditioning (A/C) evaporator, a heater core, distribution control doors and temperature control doors. On 3.0L diesel vehicles, the heater assembly also contains a positive temperature coefficient (PTC) electric booster heater.

Mounted on the heater casing are 13 stepper motors. Each of the stepper motors is connected to either a distribution control door or a temperature control door.

Note. The stepper motors are particularly susceptible to low voltage and a range of stepper motor diagnostic trouble code (DTC)'s are likely due to low voltage at engine crank. Only take note of these if it is a permanent fault that recurs persistently.

The evaporator is part of the air conditioning (A/C) system. Refer to Air Conditioning .

The heater core provides the heat source to warm the air supplied to the passenger compartment. The heater core is an aluminum two pass, fin and tube heat exchanger, and is installed across the width of the heater housing. Two aluminum tubes attached to the heater core extend through the engine bulkhead and connect to the engine cooling system.

AIR INLET DUCT

Scheme 2

The air inlet duct connects the fresh air inlet in the engine bulkhead to the heater assembly. The air inlet duct is installed behind the instrument panel on the passenger side.

The air inlet duct consists of a casing that contains a pollen filter, an air inlet door, a blower and a blower control module. A recirculation air inlet is incorporated into the casing. A servo motor mounted on the casing is connected to the air inlet door, to allow selection between fresh and recirculated air.

The pollen filter is installed in the fresh air inlet of the air inlet duct. A cover on the underside of the air inlet duct allows access for replacement of the pollen filter.

The blower regulates the volume of air flowing through the air inlet duct to the heater assembly. The blower consists of an open hub, centrifugal fan and an electric motor.

The blower control module regulates the power supply to the blower motor. The blower control module is installed in the air inlet duct downstream of the blower, where any heat generated during operation is dissipated by the air flow.

VENTILATION OUTLETS

Scheme 3

The ventilation outlets allow the free flow of air through the passenger compartment. The outlets are installed in the left-hand (LH) and right-hand (RH) rear quarter panels, behind the rear bumper. Each ventilation outlet consists of a grille covered by a soft rubber flaps, and is effectively a non-return valve. The flaps open and close automatically depending on the pressure differential between the air inside and outside the vehicle.

A/C (air conditioning) system transfers heat from the passenger compartment to the outside atmosphere to provide the heater assembly with dehumidified cold air. The A/C system is a sealed, closed loop system filled with a charge weight of refrigerant as the heat transfer medium. Depending on market, the refrigerant is either R1234yf or R134a. Oil is added to the refrigerant to lubricate the internal components of the A/C compressor. The system consists of

1. An A/C compressor
2. A condenser
3. A receiver drier
4. A thermostatic expansion valve
5. An evaporator
6. Low and high pressure refrigerant lines.

PRINCIPLES OF OPERATION

To accomplish the transfer of heat, refrigerant is circulated around a sealed system, where it passes through two pressure/temperature regimes. In each of the regimes the refrigerant changes state, during which process maximum heat absorption or dissipation 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 a liquid to a vapor in the evaporator to absorb heat.

The high pressure/temperature regime is from the compressor, through the condenser and receiver drier assembly 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 a vapor to a liquid in the condenser.

Operation of the air conditioning (A/C) system is controlled by the automatic temperature control (ATC) module. Refer to Control Components .

A/C System Flow Diagram

COMPRESSOR

The air conditioning (A/C) 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.

The air conditioning (A/C) compressor is a variable displacement unit driven by the engine accessory drive belt. On 5.0L vehicles, the air conditioning (A/C) compressor is driven directly from the pulley. On 3.0L diesel vehicles the air conditioning (A/C) compressor is driven via an electro-magnetic clutch. While the ignition is on, the clutch is permanently engaged by a power feed from the ignition relay in the engine junction box (EJB).

To protect the system from excessive pressure, a pressure relief valve is installed in the outlet side of the air conditioning (A/C) compressor. The pressure relief valve vents excess pressure into the engine compartment.

The solenoid valve enables the flow of refrigerant through the air conditioning (A/C) compressor to be adjusted to match the cooling load. Operation of the solenoid valve is controlled by the automatic temperature control (ATC) module using a hardwired drive current of differing values. By controlling the flow of refrigerant through the compressor, the solenoid valve controls the air conditioning (A/C) system pressure and the evaporator operating temperature.

CONDENSER

Scheme 4

The condenser transfers heat from the refrigerant to the surrounding air to convert the high pressure vapor from the compressor into a liquid. The condenser is installed immediately in front of the radiator. Two brackets on each end tank attach the condenser to the end tanks of the radiator.

The condenser is classified as a sub-cooling condenser and consists of a fin and tube heat exchanger core installed between two end tanks. Divisions in the end tanks separate the heat exchanger into a four pass upper (condenser) section and a two pass lower (sub-cooler) section.

The left-hand (LH) end tank provides the connections to the high pressure line from the air conditioning (A/C) compressor and the high pressure liquid line to the evaporator.

The right-hand (RH) end tank provides the connections to the receiver drier.

RECEIVER DRIER

The receiver drier is connected to the right-hand (RH) end tank of the condenser. It removes solid impurities and moisture from the refrigerant, and provides a reservoir for liquid refrigerant to accommodate changes of heat load at the evaporator. The receiver drier is part of the condenser assembly and is not serviceable separately.

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.

The thermostatic expansion valve is a block type valve located behind the heater assembly, and attached to the inlet and outlet ports of the evaporator. The thermostatic expansion valve consists of an aluminum housing containing inlet and outlet passages. A ball and spring metering valve is installed in the inlet passage and a temperature sensor is installed in the outlet passage. The temperature sensor consists of a temperature sensitive tube connected to a diaphragm. The bottom end of the temperature sensitive tube acts on the ball of the metering valve. Pressure on top of the diaphragm is controlled by the evaporator outlet temperature conducted through the temperature sensitive tube. The bottom of the diaphragm senses evaporator outlet pressure.

Liquid refrigerant flows through the metering valve into the evaporator. The restriction across the metering valve reduces the pressure and temperature of the refrigerant. The restriction also changes the liquid stream of refrigerant into a fine spray, to improve the evaporation process. As the refrigerant passes through the evaporator, it absorbs heat from the air flowing through the evaporator. The increase in temperature causes the refrigerant to vaporize and increase in pressure.

The temperature and pressure of the refrigerant leaving the evaporator acts on the diaphragm and temperature sensitive tube, which regulate the metering valve opening and so control the volume of refrigerant flowing through the evaporator. The warmer the air flowing through the evaporator, the more heat available to evaporate refrigerant and thus the greater volume of refrigerant allowed through the metering valve.

EVAPORATOR

Scheme 5

The evaporator is installed in the heater assembly, between the blower and the heater matrix, to absorb heat from the exterior or recirculated air.

Most of the moisture in the air passing through the evaporator condenses into water, which drains out of the vehicle by passing through a drain tube to the underside of the vehicle.

REFRIGERANT LINES

To maintain similar flow velocities around the air conditioning (A/C) system, the diameter of the refrigerant lines varies to suit the two pressure/temperature regimes. Larger diameter pipes are installed in the low pressure/temperature regime and smaller diameter pipes are installed in the high pressure/temperature regime.

Low and high pressure servicing connections are incorporated into the refrigerant lines for system servicing.

Petrol engine vehicles (NAS market from 14 MY)

An internal heat exchanger is installed which increases the efficiency of the evaporator and ensures any residual liquid in the low pressure line is evaporated before it reaches the compressor. Refer to the Component Location graphic titled: Petrol engine vehicles (NAS market from 14 MY).

Note. The internal heat exchanger is incorporated primarily because of the introduction of refrigerant R1234yf which replaces refrigerant R134a.

The climate control system is controlled by the ATC (automatic temperature control) module. It controls the heating and ventilation system and the A/C (air conditioning) system to regulate the temperature, volume and distribution of air into the passenger compartment. The system is either a dual zone or four zone system, depending on vehicle specification, which is fully automatic and capable of supplying individual temperature levels to each zone of the passenger compartment, up to a maximum differential of approximately 3°C (5.4°F). Manual overrides for the system include inlet air source, blower speed and air distribution. These selections can be made on the TSD (touch screen display), the ICP (integrated control panel) and, on four zone systems, the rear climate control panel.

The two and four zone climate control systems contain the same hardware. Different software in their respective ATC modules produces the different functionality required by the two systems.

AIR INLET CONTROL

The source of inlet air is automatically controlled by the automatic temperature control (ATC) module, unless overridden by pressing the air recirculation switch on the ICP (integrated control panel) to give timed or latched recirculation. A brief press of the switch illuminates the switch indicator and activates timed recirculation. Pressing and holding the switch causes the switch indicator to flash and then illuminate constantly, indicating that the air inlet is in latched recirculation and the switch can be released. A second press of the switch cancels recirculation and the automatic temperature control (ATC) module returns the recirculation door to the fresh air position. Timed recirculation is automatically cancelled after a set time, which varies with ambient air temperature.

During automatic control, the automatic temperature control (ATC) module determines the required position of the recirculation door from its 'comfort' algorithm and, if fitted, the pollution sensor. If it detects pollution, the automatic temperature control (ATC) module sets the air source to recirculation for 10 minutes, then to fresh air for 20 seconds to renew the air in the vehicle. The automatic temperature control (ATC) module repeats this cycle until the pollution is no longer present.

The sensitivity of the pollution sensor can be adjusted on the TSD (touch screen display) using the Settings button on the FRONT CLIMATE menu. The pollution sensing function can also be switched off by adjusting sensitivity to the minimum setting. If there is a fault with the pollution sensor, the automatic temperature control (ATC) module disables automatic operation of the recirculation door.

AIR TEMPERATURE CONTROL

The temperature blend doors adjust the proportion of cool air from the evaporator that passes through the heater core to produce the required output air temperature.

The temperature blend doors for each zone are operated independently to enable individual temperature settings for the different zones. The temperature blend doors are operated by stepper motors, which are controlled by the automatic temperature control (ATC) module using local interconnect network (LIN) bus messages.

The automatic temperature control (ATC) module calculates the temperature blend stepper motor positions required to achieve the selected temperature and compares it against the current position. If there is any difference, the automatic temperature control (ATC) module signals the stepper motors to adopt the new position.

Air temperature is controlled automatically unless maximum heating (HI) or maximum cooling (LO) is selected. When maximum heating or cooling is selected, a 'comfort' algorithm in the automatic temperature control (ATC) module adopts an appropriate strategy for air distribution, blower speed, and air source.

Temperature control in one zone can be compromised by another zone being set to a high level of heating or cooling. True maximum heating or cooling (displayed as HI or LO on the TSD) can only be selected for the driver's zone. If HI or LO is selected for the driver's zone, the temperature for the other zone(s) is automatically set to match the driver's zone.

If air conditioning (A/C) is selected off in the automatic mode, no cooling of the inlet air will take place. The minimum output air temperature from the system will be ambient air temperature plus any heat pick up in the air inlet path.

If the Sync climate button on the TSD is pressed, the automatic temperature control (ATC) module synchronizes the temperature of the other zone(s) with the driver's zone.

BLOWER CONTROL

When the system is in the automatic mode, the automatic temperature control (ATC) module determines the blower speed required from a comfort algorithm. When the system is in the manual mode, the automatic temperature control (ATC) module operates the blower at the speed selected using the rotary control switch on the ICP. The automatic temperature control (ATC) module also adjusts blower speed to compensate for the ram effect on inlet air produced by forward movement of the vehicle. As vehicle speed and ram effect increases, blower motor speed is reduced, and vice versa.

On vehicles fitted with the four zone system, the system cannot be turned on using the rotary blower control on the rear climate control panel. This is to encourage the use of the AUTO mode. Provided the rear climate control panel is unlocked, pressing a rear AUTO button on the rear climate control panel will reactivate the system if previously off.

AIR DISTRIBUTION CONTROL

Air distribution doors direct the air to the individual vents and registers in the passenger compartment. The doors are operated by stepper motors, which are controlled by the automatic temperature control (ATC) module using local interconnect network (LIN) bus messages.

When the air conditioning (A/C) system is in automatic mode, the automatic temperature control (ATC) module automatically controls air distribution into the passenger compartment in line with its 'comfort' algorithm. Automatic control is overridden if any of the buttons on the TSD, or switches on the ICP or rear climate control panel, are selected. Air distribution remains as selected until one of the AUTO switches is pressed or a different manual selection is made.

A/C COMPRESSOR CONTROL

When air conditioning (A/C) is selected the automatic temperature control (ATC) module maintains the evaporator at an operating temperature that varies with the passenger compartment cooling requirements. If the requirement for cooled air decreases, the automatic temperature control (ATC) module raises the evaporator operating temperature by reducing the flow of refrigerant provided by the air conditioning (A/C) compressor. The automatic temperature control (ATC) module closely controls the rate of temperature increase to avoid introducing moisture into the passenger compartment.

If the requirement for cooled air increases, the automatic temperature control (ATC) module lowers the evaporator operating temperature by increasing the flow of refrigerant provided by the air conditioning (A/C) compressor.

When air conditioning (A/C) is off, the compressor current signal supplied by the automatic temperature control (ATC) module holds the air conditioning (A/C) compressor solenoid valve in the minimum flow position, effectively switching off the air conditioning (A/C) function.

The automatic temperature control (ATC) module incorporates limits for the operating pressure of the refrigerant system. If the system approaches the high pressure limit, the compressor current signal is progressively reduced until the system pressure decreases. If the system falls below the low pressure limit, the compressor current signal is held at its lowest setting so that the air conditioning (A/C) compressor is maintained at its minimum stroke. This avoids depletion of the lubricant from the air conditioning (A/C) compressor.

A/C COMPRESSOR TORQUE

The automatic temperature control (ATC) module transmits refrigerant pressure and air conditioning (A/C) compressor current values to the engine control module (ECM) over the medium speed then high speed controller area network (CAN) bus, using the central junction box (CJB) as a gateway. The engine control module (ECM) uses these values to calculate the torque being used to drive the air conditioning (A/C) compressor. The engine control module (ECM) compares the calculated value with its allowable value and, if necessary, forces the automatic temperature control (ATC) module to inhibit the air conditioning (A/C) compressor by transmitting the 'ACClutchInhibit' controller area network (CAN) message. This forces the automatic temperature control (ATC) module to reduce the drive current to the air conditioning (A/C) compressor solenoid valve, which reduces refrigerant flow. This in turn reduces the torque required to drive the air conditioning (A/C) compressor.

By reducing the maximum air conditioning (A/C) compressor torque, the engine control module (ECM) is able to reduce the load on the engine when it needs to maintain vehicle performance or cooling system integrity.

COOLING FAN CONTROL

The automatic temperature control (ATC) module determines the amount of condenser cooling required from the refrigerant pressure sensor, since there is a direct relationship between the temperature and pressure of the refrigerant. The cooling requirement is broadcast to the engine control module (ECM) on the medium speed controller area network (CAN) bus. The engine control module (ECM) then controls the temperature of the condenser using the cooling fan.

PROGRAMMED DEFROST

The programmed defrost DEF switch is located on the ICP. When the switch is pressed, the automatic temperature control (ATC) module instigates the programmed defrost function. When selected, the automatic temperature control (ATC) module configures the system as follows

1. Automatic mode off.
2. Air conditioning (A/C) on.
3. Selected temperature unchanged.
4. Air inlet set to fresh air.
5. Air distribution set to windshield.
6. Blower speed set to level 6.

The automatic temperature control (ATC) module also sends a medium speed controller area network (CAN) message to the central junction box (CJB) to activate the windshield heater (where fitted) and rear window heater.

On vehicles fitted with the four zone system, the rear climate control panel shows a defrost symbol to indicate that the system is in defrost and no air flow will be available to the rear vents.

The programmed defrost function can be cancelled by one of the following

1. A second press of the DEF switch.
2. Selecting any air distribution switch on the TSD.
3. Pressing the driver side AUTO switch on the ICP.
4. Switching the ignition OFF.

The blower speed can be adjusted without terminating the programmed defrost function. If the blower speed has been adjusted and then the DEF switch is pressed again, the system will go back to the DEFROST default settings. Another press of the DEF switch, or pressing the driver AUTO switch, will exit the DEFROST mode but leave the heated screen(s) on.

ATC MODULE

Scheme 6

The automatic temperature control (ATC) module is mounted on the outboard end of the air inlet duct, behind the front passenger side of the instrument panel. The automatic temperature control (ATC) module processes inputs from the system sensors, the TSD, the ICP and, on four zone systems, the rear climate control panel. In response to these inputs, the automatic temperature control (ATC) module outputs control signals to the air conditioning (A/C) system and the heating and ventilation system.

Two electrical connectors provide the interface between the automatic temperature control (ATC) module and the vehicle wiring.

REFRIGERANT PRESSURE SENSOR

The refrigerant pressure sensor provides the automatic temperature control (ATC) module 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.

EVAPORATOR TEMPERATURE SENSOR

The evaporator temperature sensor is a negative temperature coefficient (NTC) thermistor that provides the automatic temperature control (ATC) module with a temperature signal from the downstream side of the evaporator. The evaporator temperature sensor is mounted directly onto the evaporator matrix fins.

The automatic temperature control (ATC) module uses the input from the evaporator temperature sensor to control the load of the air conditioning (A/C) compressor and thus the operating temperature of the evaporator.

HUMIDITY AND TEMPERATURE SENSOR

Scheme 7

The humidity and temperature sensor is behind a grill in the instrument panel, on the inboard side of the steering column. The sensor incorporates

1. A negative temperature coefficient (NTC) thermistor to measure temperature.
2. A capacitive sensor element to measure humidity.
3. A motor driven fan to draw air through the sensor and over the sensing elements.

Humidity within the passenger compartment is controlled by raising and lowering the evaporator temperature. An increase in evaporator temperature increases the moisture content of the air entering the passenger compartment. Lowering the evaporator temperature reduces the moisture content of the air entering the passenger compartment.

AMBIENT AIR TEMPERATURE SENSOR

Scheme 8

The ambient air temperature sensor is a negative temperature coefficient (NTC) thermistor that provides the automatic temperature control (ATC) module with an input of external air temperature. The sensor is hard wired to the engine control module (ECM), which transmits the temperature to the central junction box (CJB) on the high speed controller area network (CAN) bus. The central junction box (CJB) acts as a gateway and transmits the ambient air temperature on the medium speed controller area network (CAN) bus for use by other systems. The sensor is installed in the left-hand (LH) door mirror, and is accessed by removing the mirror glass, cap and actuator.

SUNLOAD SENSOR

Scheme 9

All vehicles have a sunload sensor installed in the center of the defrost grill of the instrument panel. Vehicles with a four zone systems have a second, identical, sunload sensor installed in the center of the parcel shelf.

The sunload sensor consists of two photoelectric cells that provide the automatic temperature control (ATC) module 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 the vehicle, and are used by the automatic temperature control (ATC) module to adjust blower speed, temperature and distribution to improve comfort in the individual zones.

POLLUTION SENSOR (WHERE FITTED)

The pollution sensor is attached to the center of the upper front crossmember and provides the automatic temperature control (ATC) module with separate signals of hydrocarbon levels and oxidized gas levels.

The pollution sensor allows the automatic temperature control (ATC) module to monitor the ambient air for the level of hydrocarbons and oxidized gases such as nitrous oxides, sulphur oxides and carbon monoxide, which controls the air inlet source to reduce the amount of contaminants entering the passenger compartment.