Automatic Climate Control

General
Certain cars are equipped with Automatic Climate Control (ACC). The heating and ventilation system is then controlled automatically so that the desired cabin temperature will be maintained regardless of the ambient temperature. The system always includes Air Conditioning (A/C) with recirculation.

A brief description of the ACC system is given below.

The ACC control module incorporates the following functions:
^ Automatic temperature control, including automatic control of recirculation.
^ Automatic control of air distribution.
^ Electrically heated rear window, including electrically heated door mirrors.

The A/C compressor is deactivated using the ECON button while the other functions are still controlled automatically.

The system can be switched off with the OFF button.

Pressing any of the buttons on the unit switches on the corresponding function manually. It the AUTO button is pressed again, the programmed operational mode will be resumed.

When the system is in automatic mode, only the preset temperature will normally be shown on the display. If the system automatically selects recirculation or the electrically heated rear window, this will also be indicated. To obtain a display of the fan or air distribution setting, it will be necessary to press the AUTO button once again. Manual selection of a function is always shown on the display.

Cars for certain markets are equipped with a vacuum-controlled water valve which shuts off the supply of water to the heat exchanger. The vacuum is controlled by electrically operated valve 581, which is supplied with current when microswitch 580 closes. This takes place when the heater flap moves to the closed position.

Components Of The ACC System
To enable the system to maintain the desired climate in the cabin, it will need information from a number of sensors as well as motors for operating corresponding flaps, etc.

Operation of the system is described under the following headings:
^ Communicated sensor values
^ Own sensors and flap actuator motors
^ Power supply
^ ACC control module

Communication With Other Units
The ACC control module communicates with both the main instrument display panel and the side instrument display via pins 11 and 13. The SID supplies the unit with the following information:
^ Outside temperature.
^ Background lighting level and black panel.
^ "Motor off" time.

The main instrument display panel supplies the unit with the following information:
^ Coolant temperature.
^ Speed.

Own Sensors And Flap Actuator Motors
The ACC control module makes use of its own sensors as follows:
^ Blended air temperature sensor 217 senses the temperature in the duct leading to the right-hand front floor vent. The sensor is connected via pins 32 and 14.
^ Cabin temperature sensor 218 senses the temperature of the air in the cabin. The sensor is integrated with suction fan 219 which provides an even flow of air round the sensor. The sensor is connected to pins 15 and 33 while a positive power supply for the suction fan comes from pin 16. The suction fan is grounded via pin 1 of the fan control unit connector.

^ The solar sensor for measuring solar intensity consists of 1 solar cell located under the black cover. It is connected via pins 34 and 35. The cabin interior and blended air temperature sensors are of NTC type, the electrical resistance of which varies with the temperature.

Power Supply
ACC control module 215 is supplied with power via fuses 21 and 27.

The unit is always supplied with current directly from the battery via fuse 27. This is the main power supply for the ACC system.

When the ignition switch is in the rive position, the unit is supplied with current via fuse 20. This input is used only for sensing this position.

The ventilation fan is supplied with current via fuse 3.

Pin 30 of the unit is connected to instrument lighting rheostat 9. This input controls only the background lighting of the push-button

ACC Control Module 216
The unit controls the following functions/units:
^ Ventilation fan 199 via fan speed control 220. The speed is continuously variable and the control is connected to pin 20. The voltage between the fan and the speed control is measured on pin 37.

^ Stepping motor 222 for the air blending flap which controls the flow of air through or past the heat exchanger. The motor is connected to pins 8, 27, 28 and 29.

^ Stepping motor 221 for the air distribution flap which controls the flow of air through the demister and/or cabin ventilation vents. The motor is connected to pins 23, 24, 25 and 26.

^ Servomotor 198 for the recirculation flap. When the flap is closed, air is taken from outside and when it is open (recirculation position), the air is taken from inside the cabin. The motor is connected to pins 2 and 21.

^ Electrically heated rear window 115 and electrically heated door mirrors 207, which are controlled via Integrated Central Electronics (ICE) 500. This in turn controls relay 133. Pin 39 emits a short pulse each time the electric heating elements are to be switched on or off. The relay coil voltage is measured on pin 31 to ascertain whether the relay has operated or released.

^ A/C compressor 170, which is turned on and off via the ICE. Only depressing the ECON button will affect pin 38. In the AUTO mode, the voltage is always lower than battery voltage and in the ECON mode it is close to 0 V. Normal cycling of the A/C compressor does not take place via this output but via antifrost thermostat 171.