Description

Control Components

NOTE:
A = Hardwired; N = Medium speed CAN (controller area network) bus.

NOTE:
See Heating and Ventilation, and Air Conditioning for control system outputs.









PRINCIPLES OF OPERATION

AIR INLET CONTROL
The source of inlet air is automatically controlled by the ATC (automatic temperature control) 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 ATC (automatic temperature control) 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 ATC (automatic temperature control) module determines the required position of the recirculation door from its 'comfort' algorithm and, if fitted, the pollution sensor. If it detects pollution, the ATC (automatic temperature control) 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 ATC (automatic temperature control) 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 ATC (automatic temperature control) 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 ATC (automatic temperature control) module using LIN (local interconnect network) bus messages.
The ATC (automatic temperature control) 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 (automatic temperature control) 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 (automatic temperature control) 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 A/C (air conditioning) 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 ATC (automatic temperature control) 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 ATC (automatic temperature control) module determines the blower speed required from a comfort algorithm. When the system is in the manual mode, the ATC (automatic temperature control) module operates the blower at the speed selected using the rotary control switch on the ICP. The ATC (automatic temperature control) 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 ATC (automatic temperature control) module using LIN (local interconnect network) bus messages.
When the A/C (air conditioning) system is in automatic mode, the ATC (automatic temperature control) 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 A/C (air conditioning) is selected the ATC (automatic temperature control) 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 (automatic temperature control) module raises the evaporator operating temperature by reducing the flow of refrigerant provided by the A/C (air conditioning) compressor. The ATC (automatic temperature control) 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 (automatic temperature control) module lowers the evaporator operating temperature by increasing the flow of refrigerant provided by the A/C (air conditioning) compressor.
When A/C (air conditioning) is off, the compressor current signal supplied by the ATC (automatic temperature control) module holds the A/C (air conditioning) compressor solenoid valve in the minimum flow position, effectively switching off the A/C (air conditioning) function.
The ATC (automatic temperature control) 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 (air conditioning) compressor is maintained at its minimum stroke. This avoids depletion of the lubricant from the A/C (air conditioning) compressor.

A/C COMPRESSOR TORQUE
The ATC (automatic temperature control) module transmits refrigerant pressure and A/C (air conditioning) compressor current values to the ECM (engine control module) over the medium speed then high speed CAN (controller area network) bus, using the CJB (central junction box) as a gateway. The ECM (engine control module) uses these values to calculate the torque being used to drive the A/C (air conditioning) compressor. The ECM (engine control module) compares the calculated value with its allowable value and, if necessary, forces the ATC (automatic temperature control) module to inhibit the A/C (air conditioning) compressor by transmitting the 'AC Clutch Inhibit' CAN (controller area network) message. This forces the
ATC (automatic temperature control) module to reduce the drive current to the A/C (air conditioning) compressor solenoid valve, which reduces refrigerant flow. This in turn reduces the torque required to drive the A/C (air conditioning) compressor.
By reducing the maximum A/C (air conditioning) compressor torque, the ECM (engine control module) 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 (automatic temperature control) 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 (engine control module) on the medium speed CAN (controller area network) bus. The ECM (engine control module) 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 ATC (automatic temperature control) module instigates the programmed defrost function. When selected, the ATC (automatic temperature control) module configures the system as follows:
- Automatic mode off.
- A/C (air conditioning) on.
- Selected temperature unchanged.
- Air inlet set to fresh air.
- Air distribution set to windshield.
- Blower speed set to level 6.
The ATC (automatic temperature control) module also sends a medium speed CAN (controller area network) message to the CJB (central junction box) 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:
- A second press of the DEF switch.
- Selecting any air distribution switch on the TSD.
- Pressing the driver side AUTO switch on the ICP.
- 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





The ATC (automatic temperature control) module is mounted on the outboard end of the air inlet duct, behind the front passenger side of the instrument panel. The ATC (automatic temperature control) 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 ATC (automatic temperature control) module outputs control signals to the A/C (air conditioning) system and the heating and ventilation system.
Two electrical connectors provide the interface between the ATC (automatic temperature control) module and the vehicle wiring.

REFRIGERANT PRESSURE SENSOR





The refrigerant pressure sensor provides the ATC (automatic temperature control) 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 NTC (negative temperature coefficient) thermistor that provides the ATC (automatic temperature control) 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 ATC (automatic temperature control) module uses the input from the evaporator temperature sensor to control the load of the A/C (air conditioning) compressor and thus the operating temperature of the evaporator.

HUMIDITY AND TEMPERATURE SENSOR





The humidity and temperature sensor is behind a grill in the instrument panel, on the inboard side of the steering column. The sensor incorporates:
- A NTC (negative temperature coefficient) thermistor to measure temperature.
- A capacitive sensor element to measure humidity.
- 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





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

SUNLOAD SENSOR





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 ATC (automatic temperature control) 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 ATC (automatic temperature control) 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 ATC (automatic temperature control) module with separate signals of hydrocarbon levels and oxidized gas levels.
The pollution sensor allows the ATC (automatic temperature control) 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.