Part 1
Control Components
COMPONENT LOCATION
INTRODUCTION
The ATC (automatic temperature control) module controls the A/C (air conditioning) system and the heating and ventilation system to regulate the temperature, volume, and distribution of air into the cabin.
The system is a fully automatic dual zone system capable of maintaining individual temperature levels selected for the LH (left-hand) and RH (right-hand) sides of the cabin. Manual overrides for the system include intake air source, blower speed and air distribution. These selections can be made using either the Touch Screen Display (TSD) or the control switches located below the TSD.
For information on how to operate the A/C (air conditioning) system and the heating and ventilation system, refer to the Owner's Handbook.
AUTOMATIC TEMPERATURE CONTROL MODULE
The ATC (automatic temperature control) module is mounted on the end of the blower motor casing, behind the instrument panel. The ATC (automatic temperature control) module processes inputs from the TSD, the control switches located below the TSD, and the system sensors. 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.
In addition to controlling the A/C (air conditioning) system and the heating and ventilation system, the ATC (automatic temperature control) module also controls the following:
- The seat heaters. For additional information, refer to Seats Description and Operation
- The rear window heater. For additional information, refer to Glass, Frames and Mechanisms Description and Operation
- The windshield heater. For additional information, refer to Glass, Frames and Mechanisms Description and Operation
- The exterior mirror heaters. For additional information, refer to Rear View Mirrors Description and Operation
- The steering wheel heater (if fitted). For additional information, refer to Steering Column Switches
Two electrical connectors provide the interface between the ATC (automatic temperature control) module, and the vehicle wiring. The ATC (automatic temperature control) module uses hardwired inputs from the system sensors, the LIN (local interconnect network) bus to communicate with the stepper motors and the medium speed CAN (controller area network) bus to communicate with other control modules on the vehicle.
AIR CONDITIONING COMPRESSOR SOLENOID VALVE
The A/C (air conditioning) compressor solenoid valve is integral with the A/C (air conditioning) compressor. Operation of the solenoid valve is controlled by the ATC (automatic temperature control) 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 (air conditioning) system pressure and the evaporator operating temperature.
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.
The ATC (automatic temperature control) 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 (automatic temperature control) module uses the signal from the pressure sensor to protect the refrigerant system from extremes of pressure. The ATC (automatic temperature control) module transmits the A/C (air conditioning) pressure, along with the compressor drive current value, to the instrument cluster on the medium speed CAN (controller area network) bus. These signals are broadcast to the ECM (engine control module) on the high speed CAN (controller area network) bus to allow it to calculate the torque being applied to the engine by the compressor.
To protect the system from extremes of pressure, the ATC (automatic temperature control) module sets the A/C (air conditioning) compressor to the minimum flow position if the pressure:
- Decreases to 2.1 ± 0.2 bar (31.5 ± 3 lbf/in2); the ATC (automatic temperature control) module loads the A/C (air conditioning) compressor again when the pressure increases to 2.3 ± 0.2 bar (33.4 ± 3 lbf/in2)
- Increases to 31 ± 1 bar (450 ± 14.5 lbf/in2); the ATC (automatic temperature control) module loads the A/C (air conditioning) compressor again when the pressure decreases to 26 ± 1 bar (377 ± 14.5 lbf/in2)
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.
CABIN HUMIDITY AND TEMPERATURE SENSOR
The cabin humidity and temperature sensor is installed behind a grill on the drivers side of the instrument panel. The temperature inside the cabin is measured by a NTC (negative temperature coefficient) thermistor. A motor within the sensor assembly draws cabin air in through the grill and over the thermistor. The motor is provided a battery voltage feed by a relay located within the CJB (central junction box).
Humidity inside the cabin is measured by a sensor element made up of film capacitors on different substrates. The dielectric is a polymer which absorbs or releases water proportional to the relative humidity of the air being drawn through the sensor and thus changes the capacitance of the capacitor. For protection, the sensor element is contained in a nylon mesh cover.
Humidity within the cabin is controlled by raising and lowering the evaporator temperature. An increase in evaporator temperature increases the moisture content in the air entering the cabin. Lowering the evaporator temperature reduces the moisture content in the air entering the cabin.
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) and its signal is transmitted to the instrument cluster on the high speed CAN (controller area network) bus. The instrument cluster acts as a gateway and transmits the ambient air temperature signal to the ATC (automatic temperature control) module on the medium speed CAN (controller area network) bus. The sensor is mounted on the vehicle center line behind the lower front grill, and can be accessed from underneath the vehicle.
SUNLOAD/LIGHT SENSOR
The sunload/light sensor consists of 2 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 vehicle occupants, and are used by the ATC (automatic temperature control) module to adjust blower speed, temperature and distribution to improve comfort.
NOTE:
The solar sensor is also used as part of the Autolamp feature and also contains the active anti-theft alarm indicator LED (light emitting diode). For additional information, refer to Exterior Lighting
For additional information, refer to Anti-Theft - Active
The sensor is installed in the center of the instrument panel upper surface and is powered by a 5 V feed from the instrument cluster.
POLLUTION SENSOR
Up to 2009 MY, a pollution sensor was installed only on Japanese specification vehicles. From 2009 MY, the pollution sensor is a standard fit in all markets.
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. The sensor is mounted in the RH (right-hand) front corner of the engine compartment.
The pollution sensor is powered by an ignition controlled voltage feed from the CJB (central junction box) and provides the ATC (automatic temperature control) module with separate signals of hydrocarbon and oxidized gases. With a pollution sensor fitted, the ATC (automatic temperature control) module can control the air intake source to reduce the amount of contaminants entering the cabin. This function is fully automatic, but can be overridden by manual selection of the air source using the recirculation control switch below the TSD.
If there is a fault with the sensor, the ATC (automatic temperature control) module disables automatic operation of the recirculation door.
CONTROL DIAGRAM
NOTE:
A = Hardwired; D = High speed CAN (controller area network) bus; N = Medium speed CAN (controller area network) bus; O = LIN (local interconnect network) bus
PRINCIPLES OF OPERATION
Air Intake Control
The source of intake air is automatically controlled unless overridden by pressing the air recirculation switch located below the TSD. Under 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.
The recirculation door is operated by an electric motor. The ATC (automatic temperature control) module provides analogue signals to the motor along a hardwired connection. A potentiometer in the motor supplies the ATC (automatic temperature control) 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 2 temperature blend doors operate independently to enable individual temperature settings for the left and right sides of the cabin. 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 of one side of the cabin can be compromised by the other side of the cabin 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 from the driver's side temperature control button. If 'HI' or 'LO' is selected from the driver's side, the passenger side temperature will be automatically set to match the driver's side.
When economy mode is selected by pressing the 'Econ' TSD soft button, no cooling of the intake 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 intake path.
Blower Motor Control
Operation of the blower motor is controlled by the ATC (automatic temperature control) module. The ATC (automatic temperature control) module monitors a feedback voltage from the blower motor control module. In response to the feedback voltage, the ATC (automatic temperature control) module provides a drive signal back to the blower motor control module which is used to regulate the voltage flow across the blower motor and hence regulate blower speed. The blower motor is provided with a battery voltage feed from the blower motor relay, which is located within the auxiliary junction box.
When the A/C (air conditioning) system is in automatic mode, the ATC (automatic temperature control) module determines the blower speed required from its 'comfort' algorithm. When the A/C (air conditioning) system is in manual mode, the ATC (automatic temperature control) module operates the blower at the speed selected using either the rotary control switch or the '+/-' soft buttons on the TSD.
The ATC (automatic temperature control) module also controls blower motor speed to compensate for the ram effect on intake air produced by forward movement of the vehicle. As vehicle speed, and consequently the ram effect increases, blower motor speed is reduced.