Control Components
Control Components
COMPONENT LOCATION
Control Components:
INTRODUCTION
The ATC module controls the A/C 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 and RH 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 system and the heating and ventilation system, refer to the Owner's Handbook.
AUTOMATIC TEMPERATURE CONTROL MODULE
The Automatic Temperature Control (ATC) module is mounted on the end of the blower motor casing, behind the instrument panel. The ATC module processes inputs from the TSD, the control switches located below the TSD, 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.
In addition to controlling the A/C system and the heating and ventilation system, the ATC module also controls the following:
- The seat heaters.
- The rear window heater.
- The windshield heater.
- The exterior mirror heaters.
- The steering wheel heater (if fitted).
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 Local Interconnect Network (LIN) bus to communicate with the stepper motors and the medium speed Controller Area Network (CAN) bus to communicate with other control modules on the vehicle.
AIR CONDITIONING 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 Engine Control Module (ECM) on the high speed CAN 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 module sets the A/C compressor to the minimum flow position if the pressure:
- Decreases to 2.1 ± 0.2 bar (31.5 ± 3 lbf/sq.in); the ATC module loads the A/C compressor again when the pressure increases to 2.3 ± 0.2 bar (33.4 ± 3 lbf/sq.in)
- Increases to 31 ± 1 bar (450 ± 14.5 lbf/sq.in); the ATC module loads the A/C compressor again when the pressure decreases to 26 ± 1 bar (377 ± 14.5 lbf/sq.in)
EVAPORATOR TEMPERATURE SENSOR
The evaporator temperature sensor is a Negative Temperature Coefficient (NTC) thermistor that provides the 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 ATC module uses the input from the evaporator temperature sensor to control the load of the A/C 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 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 Central Junction Box (CJB).
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 thermistor that provides the ATC module with an input of external air temperature. The sensor is hard wired to the ECM and its signal is transmitted to the instrument cluster on the high speed CAN bus. The instrument cluster acts as a gateway and transmits the ambient air temperature signal to the ATC module on the medium speed CAN 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 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 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.
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
The pollution sensor allows the ATC module to monitor the ambient air for the level of hydrocarbons and oxidised gases such as nitrous oxides, sulphur oxides and carbon monoxide. The sensor is mounted in the RH front corner of the engine compartment.
NOTE: The pollution sensor is only fitted to Japanese specification vehicles.
The pollution sensor is powered by an ignition controlled voltage feed from the CJB and provides the ATC module with separate signals of hydrocarbon and oxidised gases. With a pollution sensor fitted, the ATC 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 module disables automatic operation of the recirculation door.
CONTROL DIAGRAM
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 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 module provides analogue signals to the 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 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 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 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 module. The ATC module monitors a feedback voltage from the blower motor control module. In response to the feedback voltage, the ATC 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 system is in automatic mode, the ATC module determines the blower speed required from its 'comfort' algorithm. When the A/C system is in manual mode, the ATC module operates the blower at the speed selected using either the rotary control switch or the '±' soft buttons on the TSD.
The ATC 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.
Air Distribution Control
Two air distribution doors are used to direct air into the cabin. 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 cabin 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 cabin will remain as selected until the 'Auto' switch is pressed or a different manual selection is made.
Programmed Defrost
When the 'DEF' button is pressed, the ATC module instigates the programmed defrost function. When selected, the ATC module configures the system as follows:
- Automatic mode off
- Selected temperature unchanged
- Air inlet set to fresh air
- Air distribution set to windshield
- Blower speed set to level 6
- Windshield and rear screen heaters 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 below the TSD
- A second press of the 'DEF' button
- Switching the ignition OFF
NOTE: The blower speed can be adjusted without terminating the programmed defrost function.
A/C Compressor Control
When A/C is selected ('Econ' off) the ATC module maintains the evaporator at an operating temperature that varies with the cabin 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.
NOTE: The ATC module closely controls the rate of temperature increase to avoid introducing moisture into the cabin.
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 economy mode is selected by pressing the 'Econ' TSD soft button, 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. When the system approaches the high pressure limit the compressor current signal is progressively reduced until the system pressure decreases. When the system pressure 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 over the medium speed then high speed CAN bus, using the instrument cluster 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.
Windshield Heater
The ATC module controls operation of the windshield heater using 2 relays in the power distribution box. When a request is made for windshield heater operation, the ATC module broadcasts a message to the CJB on the medium speed CAN bus. On receipt of this message, the CJB energises the relays by providing a ground path for both relay coils. This allows a battery feed to flow across the relays to power the left and right heater elements.
NOTE: Windshield heater operation is only enabled when the engine is running.
There are 2 modes of windshield heater operation; manual and automatic.
Manual operation is activated by pressing the windshield heater control switch. When the switch is pressed, the ATC module illuminates a Light Emitting Diode (LED) in the switch and powers the heater elements for 6.5 minutes.
The switch LED remains illuminated until the windshield heater switch is pressed a second time (to switch the system off), the heating phase is completed, or the engine stops. If the engine is re-started within 30 seconds the windshield heater resumes the previous heating phase.
There are 2 variants of automatic operation; automatic operation at the start of a journey and automatic operation during a journey.
Automatic operation at the start of a journey is initiated if the ambient air temperature is below 5 degrees C (41 degrees F) at the start of a journey. In this instance, the ATC module will automatically power the windshield heater elements and illuminate the switch LED for 6.5 minutes. The windshield heater can be switched off during this period by pressing the control switch or stopping the engine.
Automatic operation during a journey is initiated when low ambient air temperatures are experienced and the vehicle has been travelling for a set period of time above a threshold speed. In this instance, no feedback is given to the driver to inform him the windshield heater is operational (the switch LED is not illuminated) and the duration of operation is variable depending upon the ambient air temperature, vehicle speed and the amount of time the vehicle has been travelling.
Rear Window Heater
The ATC module controls operation of the rear window heater using a relay in the auxiliary junction box. When a request is made for rear window heater operation, the ATC module broadcasts a message to the auxiliary junction box on the medium speed CAN bus. On receipt of this message, the auxiliary junction box energises 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.
NOTE: Rear window heater operation is only enabled when the engine is running.
There are 2 modes of rear window heater operation; manual and automatic.
Manual operation is activated by pressing the rear window heater control switch. When the switch is pressed, the ATC module illuminates a LED in the switch and powers the heater element for 21 minutes.
The switch LED remains illuminated until the rear window heater switch is pressed a second time (to switch the system off), the heating phase is completed, or the engine stops. If the engine is re-started within 30 seconds the rear window heater resumes the previous heating phase.
There are 2 variants of automatic operation; automatic operation at the start of a journey and automatic operation during a journey.
Automatic operation at the start of a journey is initiated if the ambient air temperature is below 5 degrees C (41 degrees F) at the start of a journey. In this instance, the ATC module will automatically power the rear window heater element and illuminate the switch LED for 21 minutes. The rear window heater can be switched off during this period by pressing the control switch or stopping the engine.
Automatic operation during a journey is initiated when low ambient air temperatures are experienced and the vehicle has been travelling for a set period of time above a threshold speed. In this instance, no feedback is given to the driver to inform him the rear window heater is operational (the switch LED is not illuminated) and the duration of operation is variable depending upon the ambient air temperature, vehicle speed and the amount of time the vehicle has been travelling.
Exterior Mirror Heaters
Exterior mirror heater operation is determined by ambient air temperature and windshield wiper status. When ambient air temperature reaches a pre-determined level, the ATC module broadcasts an exterior mirror heating request to the door modules over the medium speed CAN bus. On receipt of this message, the door modules provide feed and ground connections to both exterior mirror heater elements.
NOTE: Operation of the exterior mirror heaters is fully automatic and not controllable by the driver.
The amount of time the exterior mirror heaters are operational increases if the windshield wipers are switched on. This ensures the mirrors remain mist free in damp and wet conditions, where there is an increased risk of misting.
Seat Heaters
There are 4 seat heater settings available; Off, 1, 2 or 3, which can be set through the TSD. The heat setting is relayed to the vehicle occupants through a graduated display on the TSD.
Operation of the heated seats is controlled by the ATC module. When the ATC module receives a heating request from the TSD, it broadcasts a message to the CJB over the medium speed CAN bus. The CJB then provides a hardwired 12 V supply to the 3 heater elements contained within each seat. The 3 heater elements, 2 in the seat cushion and 1 in the seat squab, are wired in series.
The ATC module monitors seat temperature using a temperature sensor located in each seat cushion. The CJB provides the temperature sensors with a 5 V supply. The level of the returned voltage back to the CJB is proportional to the seat temperature. The value of the return signal is broadcast to the ATC module over the medium speed CAN bus which it then converts into a temperature value to allow it to control seat temperature to the required level.
The ATC module will suspend or disable operation of the seat heaters if any of the following occur:
- Battery voltage exceeds 16.5 ± 0.3 V for more than 5 seconds. Seat heating is re-enabled when battery voltage decreases to 16.2 ± 0.3 V
- If a short or open circuit is detected
- If the seat heat temperature rises significantly above the target temperature setting.
The graduated display on the TSD remains illuminated until the seat heaters are turned off or the engine stops. If the engine is restarted within 30 seconds the seat heater resumes the previous heating level.
Steering Wheel Heater
The steering wheel heater has 1 heat setting and can be turned on and off by pressing the soft button located on the seat heater TSD screen. The on/off status of the steering wheel heater is relayed to the vehicle occupants through the TSD. When the ignition is switched off, the heater will reset to off.
Power for the heater element is supplied by the CJB on receipt of a request from the ATC module over the medium speed CAN 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 thermistor located within the steering wheel.