Part 1
Control Components
COMPONENT LOCATIONS
NOTE:
RHD (right-hand drive) installation shown, LHD (left-hand drive) similar.
GENERAL
The control system operates the A/C (air conditioning) system and the heating and ventilation system to control the temperature, volume and distribution of air from the heater.
Either a manual or an automatic control system is installed in the vehicle. The manual system maintains a constant heater outlet temperature, to both sides of the passenger compartment, with manual control of the intake air source, blower speed and air distribution. The automatic system automatically adjusts the temperature, volume and distribution of the air from the heater to maintain the individual temperature levels selected for the LH (left-hand) and RH (right-hand) sides of the passenger compartment. The automatic system also has manual overrides for the intake air source, blower speed and air distribution. The manual and automatic systems both include:
- An ATC (automatic temperature control) module.
- An ambient air temperature sensor.
- A refrigerant pressure sensor.
- An evaporator temperature sensor.
The automatic system incorporates the following additional components:
- An in-vehicle temperature sensor.
- A sunlight sensor.
The automatic system in the Japan market also incorporates:
- A pollution sensor.
- A humidity sensor.
ATC MODULE
The ATC (automatic temperature control) module is installed in the center console. An integral control panel contains push switches and rotary switches for system control inputs. LED (light emitting diode)s in the switches and switch surrounds illuminate to indicate the current settings of the system. Switch symbols are illuminated when the side lamps or headlamps are on.
The ATC (automatic temperature control) module processes inputs from the control panel switches, system sensors and the medium speed CAN (controller area network) bus, then outputs the appropriate 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 front 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 windshield washer jet and exterior mirror heaters. For additional information, refer to Rear View Mirrors
Manual System Control Panel
Automatic System Control Panel
Inputs and Outputs
Four electrical connectors provide the interface between the ATC (automatic temperature control) module and the vehicle wiring.
The control system sensors provide hardwired inputs to the ATC (automatic temperature control) module. The ATC (automatic temperature control) module also uses the LIN (local interconnect network) bus to communicate with the auxiliary climate control system and the door motors in the heater assembly, and the medium speed CAN (controller area network) bus to communicate with other control modules on the vehicle. For additional information, refer to Communications Network
AMBIENT AIR TEMPERATURE SENSOR
The ambient 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 attached to a bracket on the rear of the bumper beam, on the vehicle center-line.
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 and 5 V, related to system pressure.
The ATC (automatic temperature control) module uses the signal from the refrigerant pressure sensor to protect the refrigerant system from extremes of pressure and to calculate A/C (air conditioning) compressor load on the engine. The ATC (automatic temperature control) module also transmits the A/C (air conditioning) compressor load value to the ECM (engine control module), via the medium speed CAN (controller area network) bus, instrument pack and high speed CAN (controller area network) bus,
for use in controlling the speed of the engine cooling fan.
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 1.9 ± 0.2 bar (27.5 ± 3 lbf/in2): the ATC (automatic temperature control) module loads the A/C (air conditioning) compressor again when the pressure increases to 2.8 ± 0.2 bar (40.5 ± 3 lbf/in2).
- Increases to 33 ± 1 bar (479 ± 14.5 lbf/in2): the ATC (automatic temperature control) module loads the A/C (air conditioning) compressor again when the pressure decreases to 23.5 ± 1 bar (341 ± 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 installed in the right side of the heater assembly casing.
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.
IN-VEHICLE TEMPERATURE SENSOR
The in-vehicle temperature sensor is a NTC (negative temperature coefficient) thermistor installed behind a grill on the driver side of the center console finisher. The sensor is connected to a tube, the other end of which is connected to a venturi on the side casing of the heater. An air bleed from the heater, through the venturi, induces a flow of air down the tube, which draws cabin air through the grill and over the sensor.
HUMIDITY SENSOR (WHERE FITTED)
The humidity sensor is a capacitive device integrated into the in-vehicle temperature sensor (see above).
The humidity sensor element is built out of a film capacitor 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.
The humidity sensor and the in-vehicle temperature sensor are connected to a PCB (printed circuit board) inside the sensor housing. The PCB is powered by a 5V feed from the ATC (automatic temperature control) module. Separate signals of temperature and relative humidity are transmitted from the PCB to the ATC (automatic temperature control) module.
SUNLIGHT SENSOR
The sunlight 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 vehicle occupants, and are used by the ATC (automatic temperature control) module to adjust blower speed, temperature and distribution to improve comfort. The sensor is installed in the center of the fascia upper surface and is powered by a 5V feed from the ATC (automatic temperature control) module.
POLLUTION SENSOR
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 attached to a bracket on the front-end carrier, at the top left corner of the condenser.
The pollution sensor is powered by a battery voltage feed from the ATC (automatic temperature control) module, and returns separate signals of hydrocarbon and oxidized gases.
If there is a fault with the pollution sensor, the ATC (automatic temperature control) module disables the automatic operation of the recirculation door.
SYSTEM OPERATION
A/C (air conditioning) Compressor Control
The variable displacement A/C (air conditioning) compressor is permanently driven by the engine. The flow of refrigerant through the A/C (air conditioning) compressor, and the resultant system pressure and evaporator operating temperature, is regulated by the refrigerant solenoid valve. Operation of the refrigerant solenoid valve is controlled by the ATC (automatic temperature control) module using a 400 Hz PWM (pulse width modulation) signal. The duty cycle of the PWM (pulse width modulation) signal is calculated using the following parameters:
- A/C (air conditioning) compressor torque.
- A/C (air conditioning) compressor torque maximum.
- A/C (air conditioning) cooling status.
- A/C (air conditioning) demand.
- A/C (air conditioning) refrigerant pressure.
- Ambient air temperature.
- Blower speed.
- Engine cranking status.
- Evaporator temperature.
- Transmission gear status.
When A/C (air conditioning) is selected, the ATC (automatic temperature control) module maintains the evaporator at an operating temperature that varies with the in-vehicle cooling requirement. The ATC (automatic temperature control) module increases the evaporator operating temperature, by reducing the refrigerant flow, as the requirement for air cooling decreases, and vice versa. During an increase of evaporator operating temperature, to avoid compromising the humidity control function, the ATC (automatic temperature control) module controls the rate of temperature increase, which keeps the cabin humidity at a comfortable level.
When the economy mode is selected, the PWM (pulse width modulation) signal holds the refrigerant 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. When the system approaches the high pressure limit, the duty cycle of the PWM (pulse width modulation) signal is progressively reduced until the system pressure decreases. When the system pressure falls below the low pressure limit, the duty cycle of the PWM (pulse width modulation) signal is held at its lowest setting, so that the A/C (air conditioning) compressor is maintained at the minimum stroke, to avoid depletion of lubricant from the A/C (air conditioning) compressor. The protection algorithm is calculated at a
high rate, to enable early detection of the rapid pressure changes possible if a system fault develops.
A/C (air conditioning) Compressor Torque
The ATC (automatic temperature control) module uses refrigerant pressure, evaporator temperature and engine speed to calculate the torque being used to drive the A/C (air conditioning) compressor. The calculated value is broadcast on the medium speed CAN (controller area network) bus for the ECM (engine control module), which uses the calculated value for idle speed control and fueling control. The ATC (automatic temperature control) module also compares the calculated value with a maximum A/C (air conditioning) compressor torque value received from the
ECM (engine control module) over the medium speed CAN (controller area network) bus. If the calculated value exceeds the maximum value, the ATC (automatic temperature control) module signals the refrigerant solenoid valve to reduce the refrigerant flow, to reduce the torque being used to drive the A/C (air conditioning) compressor. By reducing the maximum A/C (air conditioning) compressor torque value, 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.
Idle Speed Control
In order to maintain A/C (air conditioning) cooling performance, the ATC (automatic temperature control) module requests an increase in engine idle speed if the evaporator temperature starts to rise while the refrigerant solenoid valve is already set to the maximum flow rate. The increase in engine idle speed is requested in three stages, using a medium speed CAN (controller area network) bus message to the ECM (engine control module). 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
The need for a change in idle speed is determined as follows:
- If the evaporator temperature increases by 3 °C (5.4 °F), or to 6 °C (10.8 °F) above the target operating temperature, over a 10 seconds period, the first stage of idle speed increase is requested.
- When the first stage of idle speed increase is set, if the evaporator temperature increases by 3 °C (5.4 °F), or increases to 12 °C (21.6 °F) above the target operating temperature, over a 9 seconds period, the second stage of idle speed increase is requested.
- When the second stage of idle speed increase is set, if the evaporator temperature increases by 3 °C (5.4 °F), or increases to 15 °C (27 °F) above the target operating temperature, over a 10 seconds period, the third stage of idle speed increase is requested.
- When an idle speed increase is set, if the evaporator temperature decreases by 3 °C (5.4 °F) over a 10 seconds period, the next stage down of idle speed increase is requested.
Electrical Load Management
The ATC (automatic temperature control) module manages the vehicle electrical loads to:
- Maintain the vehicle battery in a healthy state of charge.
- Ensure adequate power is available for defrost demisting during engine warm-up.
- Ensure adequate power is available for A/C (air conditioning) during extended periods with the engine at idle speed.
- To maintain system voltage within acceptable limits.
- To provide adequate power to meet customer expectations.
Electrical load management is achieved by increasing the engine idle speed and controlling the electrical load of systems that do not affect the driveability or safety of the vehicle.
During the engine warm-up period, the ATC (automatic temperature control) module manages the electrical load to make sure that the battery voltage is maintained above a pre-determined level. The battery voltage level that is maintained and the duration of the start period varies with ambient air temperature and engine coolant temperature. After the engine warm-up period, the ATC (automatic temperature control) module manages the electrical load to make sure that the requested electrical load does not exceed the generator output.
The duration of the engine warm-up period depends on the ambient air temperature and the engine coolant temperature when the ignition is switched on, as detailed in the following table:
The ATC (automatic temperature control) module calculates the electrical load from the battery voltage and generator output voltage, and compares the result against the maximum load available from the generator. The calculation is averaged across the first 20 seconds after the engine starts, and subsequently averaged every 60 seconds. When the ignition is turned off, the ATC (automatic temperature control) module stores the status of the electrical load management for 20 seconds. If the engine is re-started within the 20 seconds, the ATC (automatic temperature control) module resumes electrical load management using the stored status. If the engine is re-started after the 20 seconds, the timers are reset and the
ATC (automatic temperature control) module re-calculates the status.
If the electrical load is more than the maximum load available, the ATC (automatic temperature control) module requests an increase of engine idle speed using the medium speed CAN (controller area network) bus message to the ECM (engine control module). If an electrical load imbalance remains after an increase in engine idle speed, or if the electrical load is more than the capacity of the charging system, the ATC (automatic temperature control) module reduces the electrical load by reducing the power of some vehicle systems or inhibiting their operation. The number of systems controlled depends on the electrical load reduction required. The systems controlled, and the order in which their
power is reduced or they are inhibited, are contained in three priority tables. The table used depends on the ambient air temperature, battery temperature and engine coolant temperature:
- The cold start table is used when the ambient air temperature is less than 5 °C (41 °F) and the engine coolant temperature is less than 30 °C (86 °F).
- The hot start table is used when the ambient air temperature is 5 °C (41 °F) or more and the engine coolant temperature is less than 30 °C (86 °F).
- The continuous table is used when battery temperature is more than 5 °C (41 °F) and the engine coolant temperature is more than 50 °C (122 °F).
- If none of above conditions are met, the ATC (automatic temperature control) module adopts the last used table.
Engine idle speed changes, and electrical load changes of systems not under direct control of the ATC (automatic temperature control) module (air suspension and entertainment), are initiated using the appropriate medium speed CAN (controller area network) bus message. When partial operation is requested:
- The air suspension system still performs height changes but reduces air compressor operation by not replenishing the reservoir.
- The entertainment system restricts the maximum volume level and reduces the output frequency bandwidth.