Part 2
Control Components
Cooling Fan Control
The ATC (automatic temperature control) module determines the amount of condenser cooling required from the refrigerant pressure, since there is a direct relationship between the temperature and pressure of the refrigerant. The cooling requirement is transmitted to the ECM (engine control module) in a medium speed CAN (controller area network) bus message. The ECM (engine control module) controls the condenser cooling using the cooling fan. For additional information, refer to Electronic Engine Controls Description and Operation
For additional information, refer to Electronic Engine Controls
For additional information, refer to Electronic Engine Controls
Air Temperature Control
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 discharge air temperature. On the automatic control system two temperature blend doors operate independently to enable independent temperature selection for the left and right sides of the vehicle interior. The temperature blend doors are operated by a single stepper motor on manual systems and two stepper motors on automatic systems. The stepper motor(s) are controlled by the ATC (automatic temperature control) module using LIN bus messages.
The ATC (automatic temperature control) module calculates the stepper motor position required to achieve the selected temperature and compares it against the current position, which is stored in memory. If there is any difference, the ATC (automatic temperature control) module signals the stepper motor to adopt the new position.
When maximum cooling or maximum heating is selected, the ATC (automatic temperature control) module overrides any previously selected options and sets the temperature, air source, blower speed and air distribution as detailed in the following table.
NOTE:
* Cold engine lock-out may be invoked, whereby blower operation is suspended until the engine reaches operating temperature.
On the automatic system, the temperature control of one zone can be compromised by the other zone being set to maximum heating or maximum cooling. True maximum heating or maximum cooling can only be obtained with both controls set to the same maximum state.
When the economy mode is selected, the automatic temperature control function still operates, but with no cooling capability the minimum discharge temperature achievable will be ambient air temperature plus any heat pick up in the air intake path.
Air Distribution Control
When the A/C (air conditioning) is in the automatic mode, the ATC (automatic temperature control) module automatically controls air distribution according to a comfort strategy. Automatic control is overridden when one of the manual modes is selected. Air distribution remains manually controlled until the automatic mode is selected again. The distribution doors are operated by two stepper motors, which are controlled by the ATC (automatic temperature control) module using LIN bus messages.
When air distribution is selected to a combination of face and feet, if the air is being heated the distribution is biased towards the feet. If the air is being cooled the distribution is biased towards the face.
Blower Control
When A/C (air conditioning) is selected or the blower speed is manually selected, the ATC (automatic temperature control) module energizes the coil of the blower relay in the BJB (battery junction box). The energized blower relay supplies battery power to the blower motor, which is grounded through the blower control module. The speed of the blower is controlled by a PWM (pulse width modulation) signal from the ATC (automatic temperature control) module to the blower control module. The blower control module regulates the blower motor voltage in relation to the
PWM (pulse width modulation) signal.
When the blower is in the automatic mode the ATC (automatic temperature control) module determines the blower speed required from the comfort algorithms. When the blower is in the manual mode, the ATC (automatic temperature control) module operates the blower at one of seven fixed speeds as selected on the control panel.
Programmed Defrost
The programmed defrost function automatically provides the maximum defrosting of the vehicle. When the programmed defrost function is selected, the ATC (automatic temperature control) module configures the control system as follows:
- Automatic mode off.
- Air inlet to fresh air, manual control.
- Selected temperature unchanged, automatic control.
- Air distribution set to screen mode, manual control.
- Blower speed set to speed 5, manual control.
- Rear screen heater and windshield heater (if applicable) selected on.
- A/C (air conditioning) mode in automatic.
The programmed defrost function is cancelled by one of the following:
- Selecting any distribution switch. The system response will be identical to the normal manual distribution control operation.
- Selecting the automatic switch. This will restore the system to fully automatic operation.
- Selecting the programmed defrost switch again. This returns the system to the state in use immediately before the programmed defrost function was first selected.
- Turning the ignition off.
The blower speed can be adjusted manually without terminating the programmed defrost function.
Intake Air Control
The source of intake air is automatically controlled unless overridden by manual selection of recirculation. Under automatic control the ATC (automatic temperature control) module determines the required position of the recirculation door from the comfort strategy and the input from the pollution sensor (if fitted). The recirculation door is operated by an electric motor, which is controlled by hardwired analogue signals from the ATC (automatic temperature control) module. A potentiometer in the motor supplies the ATC (automatic temperature control) module with a position feedback signal for closed loop control.
Provided the intake air has not been manually selected to recirculation, the ATC (automatic temperature control) module adjusts the recirculation door to reduce the ram effect produced by the forward motion of the vehicle.
When the ignition switch is turned off, the ATC (automatic temperature control) module evaluates the ambient air temperature. If the ambient air temperature is less than a pre-determined value, the intake air source is set to recirculation, to prevent the ingress of damp air while the vehicle is parked.
When the vehicle is in the transportation mode, the ATC (automatic temperature control) module sets the intake door to recirculation every time the ignition is turned off, regardless of the ambient air temperature.
Pollution Sensing
With a pollution sensor fitted to the vehicle, the ATC (automatic temperature control) module controls the intake air source to reduce contamination of the intake air by external pollutants. This function is fully automatic, but can be overridden by manual selection of the intake air source.
Humidity Sensing
With a humidity sensor fitted, the ATC (automatic temperature control) module controls the moisture content of the air in the vehicle. This is achieved by raising the evaporator temperature to increase the humidity of the air entering the vehicle, and reducing the evaporator temperature to reduce the humidity of the air entering the vehicle.
Front Seat Heaters
The front seat heaters are enabled when the ignition switch is position II, and operate at one of two temperature settings. With the first press of a front seat heater switch the ATC (automatic temperature control) module adopts the higher temperature setting, supplies a power feed to the related front seat heater elements and illuminates two amber LED (light emitting diode)s in the switch. At the second press of the switch the ATC (automatic temperature control) module adopts the lower temperature setting and extinguishes one of the LED (light emitting diode)s. At the third press of the switch the
ATC (automatic temperature control) module de-energizes the heater elements and extinguishes the second LED (light emitting diode). The seat heaters remain on until selected off or the ignition is turned off.
The ATC (automatic temperature control) module receives an input from a temperature sensor in each front seat, and regulates the power feed of the heater elements to control the seat temperature at the appropriate temperature setting between 35 and 45 °C (95 and 113 °F). The actual temperature settings vary with the type of seat covering, to allow for the different heat conduction properties of the different materials.
When the front seat heaters are activated at the higher temperature setting, the ATC (automatic temperature control) module automatically resets them to the lower temperature after a time delay. The length of the time delay depends on the in-vehicle temperature.
To protect the heater elements, the ATC (automatic temperature control) module disables front seat heating if battery voltage exceeds 16.5 ± 0.3 volts for more than 5 seconds. Front seat heating is re-enabled when battery voltage decreases to 16.2 ± 0.3 volts.
The ATC (automatic temperature control) module monitors the power feeds to the heater elements and disables the applicable front seat heating if a short or open circuit is detected. The ATC (automatic temperature control) module also disables seat heating if the seat temperature rises significantly above the target temperature setting.
The plausibility of the temperature sensor inputs is also monitored by the ATC (automatic temperature control) module. When seat heating is selected, if one of the temperature sensor inputs is within 5 °C (9 °F) below the target temperature, the ATC (automatic temperature control) module monitors the sensor input for a temperature increase and checks that it is between the minimum and maximum working temperatures. If a temperature sensor input is at the high end of the working range, while the ambient air temperature and the engine temperature are within 10 °C (18 °F) of each other, the ATC (automatic temperature control) module disables front seat heating until the input decreases below the target temperature setting. The
ATC (automatic temperature control) module interprets a temperature sensor input value of -45 °C (-49 °F) or below as an open circuit, and temperature sensor input value of 100 °C (212 °F) or more as a short circuit.
Rear Window Heater
The ATC (automatic temperature control) module controls operation of the rear window heater using medium speed CAN (controller area network) messages to operate the rear window heater relay in the CJB (central junction box). The control module in the CJB (central junction box) interprets the CAN (controller area network) messages and switches the ground connection of the relay coil to operate the rear window heater. While the rear window heater relay is energized, a battery power feed is connected to the rear window heater elements. Rear window heater operation is only enabled when the engine is running.
The ATC (automatic temperature control) module operates the rear window heater in heating cycles of varying power and time. The heating cycle used depends on the ambient air temperature and whether it is the initial or subsequent operation during the current ignition cycle.
When the rear window heater switch is pressed, the ATC (automatic temperature control) module illuminates an LED (light emitting diode) in the switch and initiates the appropriate heating cycle. The LED (light emitting diode) remains illuminated until the rear window heater is selected off, the heating cycle is completed or the engine stops. If the engine stalls or the ignition is turned off, rear window heating resumes if the engine is re-started within 20 seconds.
On the initial selection of rear window heating, the ATC (automatic temperature control) module uses a short or long defrost phase at full power, followed by a low power phase. The defrost phase used depends on the ambient temperature. During the low power phase, the rear window heater relay is cycled off for 80 seconds and on for 40 seconds.
On subsequent operations, during the same ignition cycle, the ATC (automatic temperature control) module operates the rear window heater at full power for a fixed time period.
Windshield Heater
The ATC (automatic temperature control) module controls operation of the windshield heater using the windshield heater relay in the BJB (battery junction box). The ATC (automatic temperature control) module switches the ground connection of the relay coil to operate the windshield heater. While the windshield heater relay is energized, a battery power feed is connected to each of the two windshield heater elements. Windshield heater operation is only enabled when the engine is running.
The ATC (automatic temperature control) module operates the windshield heater in heating cycles of varying power and time. The heating cycle used depends on the ambient air temperature and whether it is the initial or subsequent operation during the current ignition cycle.
When the windshield heater switch is pressed, the ATC (automatic temperature control) module illuminates an LED (light emitting diode) in the switch and initiates the appropriate heating cycle. The LED (light emitting diode) remains illuminated until the windshield heater is selected off, the heating cycle is completed or the engine stops. If the engine stalls or the ignition is turned off, windshield heating resumes if the engine is re-started within 20 seconds.
On the initial selection of the windshield heater, the ATC (automatic temperature control) module uses a short or long defrost phase at full power, followed by a low power phase. The defrost phase used depends on the ambient temperature. During the low power phase, the windshield heater relay is cycled off for 80 seconds and on for 40 seconds.
On subsequent operations, during the same ignition cycle, the ATC (automatic temperature control) module operates the windshield heater at full power for a fixed time period.
MANUAL SYSTEM CONTROL DIAGRAM
NOTE:
A = Hardwired connections; D = High speed CAN (controller area network) bus; N = Medium speed CAN (controller area network) bus; O = LIN bus
AUTOMATIC SYSTEM CONTROL DIAGRAM
NOTE:
A = Hardwired connections; D = High speed CAN (controller area network) bus; N = Medium speed CAN (controller area network) bus; O = LIN bus
