Part 1

Control Components

COMPONENT LOCATIONS

NOTE:
RHD (right-hand drive) installation shown; LHD (left-hand drive) installation 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.
The system is a dual zone system that 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 system also has manual overrides for the intake air source, blower speed and air distribution. The system includes:
- An ATC (automatic temperature control) module.
- An ambient temperature sensor.
- A refrigerant pressure sensor.
- An evaporator temperature sensor.
- An in-vehicle temperature sensor.
- A sunlight sensor.
Vehicles in the Japan market also incorporate:
- A pollution sensor.
- A humidity sensor.

ATC (automatic temperature control) 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) 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
- The windshield heater. For additional information, refer to Glass, Frames and Mechanisms
- The windshield washer jets and exterior mirror heaters. For additional information, refer to Rear View Mirrors

Control Panel









The switches on the ATC (automatic temperature control) module control panel have the following functions:
- LH and RH Temperature Switches: Adjusts the nominal temperature settings of the LH (left-hand) and RH (right-hand) sides of the passenger compartment. The switch can rotate through 270°, between full cold and full hot. The switch surrounds are graduated in 2° increments between 16 and 28 °C. Minor detents define 1 °C steps over the range of the switch. Amber LED (light emitting diode)s in the switch surround illuminate to indicate the temperature setting. When maximum cold is selected, the ATC (automatic temperature control) module also automatically sets the air source to recirculated air, blower speed to maximum and distribution to face. When maximum hot is selected, the
ATC (automatic temperature control) module also automatically sets the air source to fresh air, blower speed to maximum and distribution to footwell.
- LH and RH Seat Heater Switches: Activates the heater elements in the seat cushion and seat back at one of two heat levels. The first press of the switch energizes the heater elements at the higher heat setting and illuminates two LED (light emitting diode)s in the switch. A second press of the switch sets the heater elements to the lower heat setting and extinguishes one of the LED (light emitting diode)s. A further press of the switch 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 switched off.
- Blower Switch: For manual adjustment of blower speed. The switch can rotate through 240°, from off to maximum speed. Eight primary detents define the off position and seven blower speeds. Minor detents define small steps between the primary detents. When blower speed is manually adjusted, amber LED (light emitting diode)s in the switch surround illuminate to indicate the selected blower speed. The LED (light emitting diode)s remain off when blower speed is under automatic control.
- Automatic Mode Switch: Activates the automatic modes for the A/C (air conditioning) system, blower speed and distribution. Separate amber LED (light emitting diode)s in the automatic mode switch illuminate to show when the blower and the distribution are in automatic mode. Manually selecting the blower speed or a distribution switch extinguishes the related LED (light emitting diode).
- Programmed Defrost Switch: Activates a program that automatically selects: inlet air to fresh air; distribution to screen only; blower to speed 5; rear screen heater on; windshield heater on (where fitted), A/C (air conditioning) system to automatic mode. An amber LED (light emitting diode) in the switch is illuminated while the defrost program is active.
- Windshield Heater Switch: Energizes the windshield heater for a set time period, until the switch is pressed again or until the engine stops, whichever occurs first. An amber LED (light emitting diode) in the switch is illuminated while the heater is on.
- Rear Window Heater Switch: Enabled only with the engine running. Pressing the switch energizes the rear window heater for a set time period, until the switch is pressed again or until the engine stops, whichever occurs first. An amber LED (light emitting diode) in the switch is illuminated while the heater is on.
- Off Switch: Switches off all of the functions controlled by the ATC (automatic temperature control) module (all tell-tale LED (light emitting diode)s are extinguished). The temperature blend door is set to the full cold position (if the A/C (air conditioning) system is in the automatic mode, if the A/C (air conditioning) system is in the economy mode the current door position is retained); the air source is set to recirculation; the current distribution settings are retained; the blower speed is set to zero. Where fitted, the seat heater switches can still be operated without re-activating the
ATC (automatic temperature control) module. The ATC (automatic temperature control) module is re-activated, with all functions in the previous operating state, by a second press of the off switch or by pressing the economy switch. The ATC (automatic temperature control) module can also be re-activated, with the associated effect, by the following switches:
- The automatic mode switch.
- Any air distribution switch.
- The blower switch.
- The programmed defrost switch.
- The recirculation switch.
- Economy Switch: Reduces the A/C (air conditioning) compressor output to a minimum displacement condition x 5%, reducing the engine load required to operate the A/C (air conditioning) compressor. An amber LED (light emitting diode) in the switch is illuminated when the economy mode is selected on.
- Recirculation Switch: For selection of fresh or recirculated air. On models without pollution sensing, an amber LED (light emitting diode) in the switch is illuminated when recirculated air is selected. On models with pollution sensing, the recirculation switch incorporates two amber LED (light emitting diode). The first press of the switch sets the recirculation flaps to automatic mode and illuminates one LED (light emitting diode). A second press of the switch manually selects recirculated air and illuminates the second LED (light emitting diode). A further press of the switch manually selects fresh air and extinguishes the two
LED (light emitting diode)s.
- Distribution Switches (Windshield, Face and Footwell): For manual selection of air distribution in any combination of windshield, face and footwell outlets. Each switch has a LED (light emitting diode) which illuminates when the related distribution mode is selected.

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 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

ATC (automatic temperature control) Module Harness Connectors

NOTE:
A = C1629; B = C1630; C = C2655; D = C2295





















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 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 cluster 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 in the instrument panel, on the inboard side of the steering column. 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 constructed from 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.
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 instrument panel upper surface and is powered by a 5V feed from the ATC (automatic temperature control) module.

POLLUTION SENSOR (WHERE FITTED)





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 dehumidification 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 and so 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
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.