2010 JAGUAR XFR compressor

Published: 11-May-2011
Climate Control - Air Conditioning - System Operation and Component Description
Description and Operation


General System 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 A/C (air conditioning) system is controlled by the ATC (automatic temperature control) module.
Refer to: Control Components (412-01 Climate Control, Description and Operation). The A/C system works in conjunction with: The air distribution and filtering system.
Refer to: Air Distribution and Filtering (412-01 Climate Control, Description and Operation). The heating and ventilation system.
Refer to: Heating and Ventilation (412-01 Climate Control, Description and Operation).

1 Evaporator 2 Thermostatic expansion valve 3 High pressure servicing connection 4 Refrigerant pressure sensor 5 Engine cooling fan 6 Condenser 7 Receiver/Drier 8 A/C compressor 9 Low pressure servicing connection 10 Blower NOTE: A = Refrigerant liquid; B = Refrigerant vapor; C = Air flow.

1 Pressure relief valve 2 Outlet port 3 Inlet port 4 Solenoid valve 5 Electrical connector 6 Pulley The 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 A/C compressor is a permanently engaged variable displacement unit which is driven by the engine accessory drive belt. To protect the system from excessive pressure, a pressure relief valve is installed in the outlet side of the A/C compressor. The pressure relief valve vents excess pressure into the engine compartment.

Item Description 1 RH (right-hand) end tank 2 Condenser core 3 LH (left-hand) end tank 4 Mounting brackets (4 off) 5 High pressure compressor discharge line connector block 6 High pressure liquid outlet line connector block 7 Receiver/Drier outlet pipe 8 Receiver/Drier inlet pipe 9 Receiver/Drier 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 LH end tank provides the connections to the high pressure line from the A/C compressor and the high pressure liquid line to the evaporator.
The RH end tank provides the connections to the receiver drier.
Receiver Drier

The receiver drier is integrated into the RH end tank of the condenser to remove solid impurities and moisture from the refrigerant. It also provides a reservoir for liquid refrigerant to accommodate changes of heat load at the evaporator.


NOTE: The receiver drier is part of the condenser assembly and is not serviceable separately.

Refrigerant entering the receiver drier passes through a filter and a desiccant pack, then collects in the base of the unit before
flowing through the outlet pipe back to the condenser. Condenser

7 LH (left-hand) temperature blend stepper motor 8 Control switches 9 Humidity and temperature sensor 10 Air inlet servo motor 11 Blower 12 ATC (automatic temperature control) module 13 Blower control module 14 Face/Feet distribution stepper motor 15 Refrigerant pressure sensor 16 A/C (air conditioning) compressor solenoid valve

6 TSD (touch screen display) 7 Integrated control panel 8 Evaporator temperature sensor 9 Humidity and temperature sensor 10 Sunload sensor 11 Refrigerant pressure sensor 12 Pollution sensor Comments:
where fitted 13 Air inlet servo motor 14 A/C (air conditioning) compressor solenoid valve 15 RH (right-hand) outer face level register 16 RH inner face level register 17 LH (left-hand) inner face level register 18 LH outer face level register 19 RH temperature blend stepper motor 20 Face/Feet distribution stepper motor 21 ATC (automatic temperature control) module 22 LH temperature blend stepper motor 23 Windshield (Defrost) stepper motor 24 Blower control module 25 RJB (rear junction box) 26 Blower


Air Inlet Control System Operation

The source of inlet air is automatically controlled unless overridden by pressing the air recirculation switch on the integrated
control panel. During automatic control, the ATC module determines the required position of the recirculation door from its 'comfort' algorithm and, if fitted, the pollution sensor.

The ATC module provides analogue signals to the air inlet servo motor along a hardwired connection. A potentiometer in the motor supplies the ATC module with a position feedback signal for closed loop control.
Air Temperature Control

Cooled air from the evaporator enters the heater assembly, where temperature blend doors direct a proportion of the air
through the heater core to produce the required output air temperature.

The two temperature blend doors operate independently to enable individual temperature settings for the left and right sides
of the passenger compartment. The temperature blend doors are operated by stepper motors, which are controlled by the ATC module using LIN bus messages.
The 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 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 ATC module adopts an appropriate strategy for air distribution, blower speed, and air source.

Temperature control in one side of the passenger compartment can be compromised by the other side of the passenger
compartment 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 side of the passenger compartment. If 'HI' or 'LO' is selected for the driver's side, the
temperature for the front passenger's side is automatically set to match the driver's side.

If 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 Temp. sync. soft button on the TSD is pressed, the ATC module synchronizes the temperature of the passenger side of the passenger compartment with the driver's side.

Blower Control

When the system is in the automatic mode, the ATC module determines the blower speed required from a comfort algorithm. When the system is in the manual mode, the ATC module operates the blower at the speed selected using either the rotary

control switch on the integrated control panel or the + and - soft buttons on the touch screen display (TSD). The 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.

Air Distribution Control

Two air distribution doors are used to direct air into the passenger compartment. The doors are operated by stepper motors,
which are controlled by the ATC module using LIN bus messages.
When the A/C system is in automatic mode, the ATC module automatically controls air distribution into the passenger compartment in line with its 'comfort' algorithm. Automatic control is overridden if any of the TSD air distribution soft buttons
are selected. Air distribution in the passenger compartment will remain as selected until the 'Auto' switch is pressed or a
different manual selection is made.

A/C Compressor Control

When A/C is selected the 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 ATC module raises the evaporator operating temperature by reducing the flow of refrigerant provided by the A/C compressor. The 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 ATC module lowers the evaporator operating temperature by increasing the flow of refrigerant provided by the A/C compressor.
When A/C is off, the compressor current signal supplied by the ATC module holds the A/C compressor solenoid valve in the minimum flow position, effectively switching off the A/C function.
The 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 A/C compressor is maintained at its minimum stroke. This avoids depletion of the lubricant from the A/C compressor.
A/C Compressor Torque

The ATC module transmits refrigerant pressure and A/C compressor current values to the ECM (engine control module) over the medium speed then high speed CAN bus, using the CJB as a gateway. The ECM uses these values to calculate the torque being used to drive the A/C compressor. The ECM compares the calculated value with its allowable value and if necessary forces the ATC module to inhibit the A/C compressor by transmitting the 'ACClutchInhibit' CAN message. This forces the ATC module to reduce the drive current to the A/C compressor solenoid valve, which reduces refrigerant flow. This in turn reduces the torque required to drive the A/C compressor.
By reducing the maximum A/C compressor torque, the 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 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 ECM on the medium speed CAN bus. The ECM then controls the temperature of the condenser using the cooling fan.
Programmed Defrost

The programmed defrost DEF switch is located on the integrated control panel. When the switch is pressed, the ATC module instigates the programmed defrost function. When selected, the ATC module configures the system as follows:
Automatic mode off.
A/C on. Selected temperature unchanged.
Air inlet set to fresh air.
Air distribution set to windshield.
Blower speed set to level 6.
Windshield heater (where fitted) and rear window heater on.
The programmed defrost function can be cancelled by one of the following:
Selecting any air distribution switch on the TSD.
Pressing the AUTO switch on the integrated control panel.
A second press of the DEF button.
Switching the ignition OFF.
The blower speed can be adjusted without terminating the programmed defrost function.

Rear Window Heater

Rear window heater operation is only enabled when the engine is running. The ATC module controls operation of the rear window heater using a relay in the RJB. When rear window heater operation is required, the ATC module broadcasts a message to the RJB on the medium speed CAN bus. On receipt of the message, the RJB energizes the relay by providing a ground path for the relay coil. This allows a battery feed to flow across the relay to power the rear window heater element.

bus. Temperature control for the heater element is provided by the steering wheel heater control module which receives a
temperature feedback signal from a NTC (negative temperature coefficient) thermistor located within the steering wheel.



ATC Module Component Description



The ATC module is mounted on the outboard end of the air inlet duct, behind the front passenger side of the instrument panel. The ATC module processes inputs from the TSD, the switches on the integrated control panel and the system sensors. In response to these inputs, the ATC module outputs control signals to the A/C system and the heating and ventilation system.
Two electrical connectors provide the interface between the ATC module and the vehicle wiring. The ATC module uses hardwired inputs from the system sensors, the LIN bus to communicate with the stepper motors and the medium speed CAN bus to communicate with other control modules on the vehicle.

A/C Compressor Solenoid Valve

The A/C compressor solenoid valve is integral with the A/C compressor. Operation of the solenoid valve is controlled by the ATC module using a hardwired drive current of differing values. By controlling the flow of refrigerant through the compressor, the
solenoid valve can control the A/C system pressure and the evaporator operating temperature.
Refrigerant Pressure Sensor



The refrigerant pressure sensor provides the 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.

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

The ATC module uses the signal from the pressure sensor to protect the refrigerant system from extremes of pressure. The ATC module transmits the A/C pressure, along with the compressor drive current value, to the instrument cluster on the medium speed CAN bus. These signals are broadcast to the ECM on the high speed CAN bus to allow it to calculate the torque being applied to the engine by the compressor. www.JagDocs.com