Part 1
Control Components
COMPONENT LOCATION
OVERVIEW
The climate control system incorporates the heating, ventilation and A/C systems. There are 2 main types of climate control system available;
^ a single zone manual system
^ a dual zone automatic system.
The climate control functions for both systems are controlled by the ATC module. The ATC module is mounted in the center console and contains both the system electronic software and user controls.
The ATC module works in conjunction with a number of other vehicle control modules, including the Engine Control Module (ECM), which controls a number of climate control sub-systems on receipt of requests from the ATC module.
The single zone climate control system features manual control for air temperature, air distribution and air source, although a small amount of automatic control does exist in the ATC software. In response to system inputs, the ATC module controls the operation of 3 stepper motors mounted on the heater assembly. The stepper motors then adjust the position of the air temperature, air distribution and air source flaps accordingly.
The dual zone climate control system features automatic control of air temperature, air distribution and blower motor speed. The ATC module is also able to control individual temperature requests for both the driver and passenger side of the cabin.
NOTE: The ATC module can only maintain a maximum temperature difference between the 2 sides of the cabin of up to approximately 3 degrees C (4 degrees F). This is due to the movement and mix of air within the cabin.
The dual zone climate control system features 2 additional sensors; a cabin temperature sensor and a sunload sensor. The cabin temperature sensor provides a temperature feedback to enable the ATC module software maintain a constant cabin temperature. The sunload sensor provides a reading of solar loading on the vehicle occupants and enables the ATC module to adjust the output from the climate control system accordingly.
Higher specification versions of the dual zone climate control system are also available. These systems feature 2 more additional sensors; a pollution sensor and a cabin humidity sensor.
The pollution sensor detects pollutants entering the cabin, allowing the ATC module to react by changing the position of the air intake flap. The cabin humidity sensor calculates the probability of misting on the windshield. The ATC module monitors the signal from the cabin humidity sensor and adjusts blower speed, air distribution and A/C compressor displacement accordingly.
ATC MODULE
The ATC module is mounted in the center console and is integral with the control panel. The module works in conjunction with the ECM to control all aspects of heating, ventilation, and A/C. An 18-pin electrical connector on the rear of the module provides hardwired, Controller Area Network (CAN) bus and Local Interconnect Network (LIN) bus connections to allow interaction with A/C system components and other vehicle control modules.
Six different ATC modules (2 single zone, 4 dual zone) are available, depending on vehicle specification. Low specification vehicles feature 3 rotary controllers and 3 top hinged momentary switches to control the quality, temperature and distribution of air into the cabin. High specification vehicles feature 3 rotary controllers, 6 top hinged momentary switches, and 2 dual function momentary switches to control the quality, temperature and distribution of air into the cabin.
In addition to the A/C system, the ATC module controls operation of:
^ The seat heaters
^ The rear window heater
^ The windshield heater
^ The exterior mirror heaters.
COMPRESSOR SOLENOID VALVE
The compressor solenoid valve is integral with the A/C compressor. Operation of the solenoid valve is controlled by the ECM using a Pulse Width Modulated (PWM) signal of differing values. By controlling the flow of refrigerant (displacement) through the compressor, the solenoid valve can control evaporator operating temperature and cabin humidity by varying the pressure within the A/C system.
NOTE: The A/C compressor solenoid valve is fitted to i6 petrol vehicles only.
REFRIGERANT PRESSURE SENSOR
The refrigerant pressure sensor provides the ECM with a pressure input from the high pressure side of the refrigerant system. The pressure sensor is located in the refrigerant line between the condenser and the thermostatic expansion valve.
The ECM supplies a 5 V reference feed to the pressure sensor and receives a return signal voltage, between 0 V and 5 V, related to system pressure. The ECM uses the signal from the sensor to protect the refrigerant system from extremes of pressure.
If the pressure within the refrigerant system exceeds the minimum or maximum pressure limits, the ECM will;
^ disable the A/C compressor (TD4 vehicles)
^ reduce A/C compressor displacement (i6 vehicles).
If a reduction in A/C compressor displacement fails to bring the system back into it's optimum pressure range, the i6 ECM will disable the A/C compressor.
The ECM constantly sends a refrigerant system pressure signal to the ATC module. The signal is transmitted from the ECM to the Central Junction Box (CJB) over the high speed CAN bus. The CJB acts as a gateway and provides the pressure signal to the ATC module over the medium speed CAN bus.
If the pressure within the refrigerant system rises above its maximum pressure limit, the ATC module will increase the amount of recirculated air entering the cabin. This helps lower the pressure within the refrigerant system and thus helps to avoid having to disable the A/C compressor.
EVAPORATOR TEMPERATURE SENSOR
The evaporator temperature sensor is a Negative Temperature Coefficient (NTC) thermistor. The sensor is mounted on the LH side of the heater casing, and measures the temperature of cooled air once it has traveled over the evaporator. The sensor receives a 5 V reference feed from the ATC module. By monitoring the returned voltage, the ATC module can calculate the resistance of the sensor and hence evaporator temperature.
CABIN TEMPERATURE SENSOR
The cabin temperature sensor comprises a NTC thermistor and a motor. The sensor is mounted behind a grill on the drivers side of the instrument panel, adjacent the steering column.
NOTE: The cabin temperature sensor is only fitted to vehicles with a dual zone, automatic climate control system.
The motor is provided an electrical feed from the ATC module and draws cabin air in through the grill and over the thermistor. The thermistor receives a 5 V reference feed from the ATC module. By monitoring the returned voltage, the ATC module can calculate air temperature within the cabin.
CABIN HUMIDITY SENSOR
The cabin humidity sensor is located within the interior mirror and comprises 3 individual elements:
^ A humidity sensor
^ An air temperature sensor
^ A windshield glass temperature sensor.
NOTE: The cabin humidity sensor is an optional fit only.
The readings from these 3 sensors combine to reduce the risk of misting on the windshield.
The humidity sensor element is contained behind a nylon mesh cover. The sensor comprises an element made up of film capacitors on different substrates. The dielectric is a polymer which absorbs or releases water proportional to the humidity of the air being drawn through the sensor. This causes a change in the capacitance of the sensor.
Humidity within the cabin is controlled by raising or lowering the temperature of the evaporator. An increase in evaporator temperature increases the moisture content of the air in the cabin. Lowering the evaporator temperature reduces the moisture content of the air in the cabin.
The capacitance of the sensor, together with both temperature values, are provided as LIN bus messages to the ATC module. The ATC module uses these signals to calculate the dew point of the air at the windshield. When the temperature of the windshield glass reaches or falls below this value, misting is likely to occur. In this instance, the ATC module will;
^ raise the temperature of the air leaving the heater assembly
^ adjust the position of the windshield distribution (defrost) stepper motor
^ adjust the position of the air intake stepper motor
^ reduce A/C compressor displacement (i6 only)
^ power the windshield heater elements (if fitted).
AMBIENT AIR TEMPERATURE SENSOR
The ambient air temperature sensor is a NTC thermistor, and is mounted in the LH door mirror. The sensor receives a 5 V reference feed from the ECM. By monitoring the returned voltage, the ECM can calculate the resistance of the sensor and hence ambient air temperature. The ECM transmits an ambient air temperature value over the high speed CAN bus. This value is relayed to the ATC module by the CJB over the medium speed CAN bus.
SUNLOAD SENSOR
The sunload sensor is mounted in the center of the instrument panel upper surface. The sensor contains a photoelectric cell, which provides the CJB with an input of light intensity equating to the solar heating effect on the cabin.
The solar heating value is transmitted from the CJB to the ATC module over the medium speed CAN bus. The ATC module compensates for the solar heating effect by adjusting blower speed, air output temperature and air distribution to maintain the required cabin temperature.
POLLUTION SENSOR
The pollution sensor allows the ATC module to monitor intake air for the level of carbon monoxide (CO) and oxides of nitrogen (NOx). The sensor is mounted on the RH side of the heater casing.
NOTE: The pollution sensor is an optional fit on vehicles with a dual zone, automatic climate control system.
The pollution sensor is provided an ignition controlled feed from the Battery Junction Box (BJB) and provides one of the following 4 signals to the ATC module based on ambient air quality:
^ Static or reduced pollution levels
^ Small increase in pollution levels
^ Medium increase in pollution levels
^ Rapid or large increase in pollution levels.
Based on the signal from the pollution sensor, the ATC module is able to control the intake air 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 intake source using the fresh/recirculated air switch on the control panel.
CONTROL DIAGRAM
