Automatic Climate Control
GENERALSome cars are equipped with an Automatic Climate Control (ACC) system. The heating and ventilation system (including A/C) is then controlled automatically so that the desired temperature in the cabin is maintained at all times, regardless of the outside temperature. Air conditioning (A/C) with a recirculation mode is always included in the ACC system.
The climate control unit has the following functions:
^ Automatic temperature control, including automatic control of recirculation.
^ Rear door fans.
^ Electrically heated rear window.
^ Electrically heated door mirrors.
The A/C compressor can be deactivated by means of the ECON button while the other functions remain under automatic control.
The system can be switched off with the OFF button. By pressing one of the buttons on the right of the unit, the particular function can be switched on manually. If the button is pressed again, the function returns to the programmed mode.
Light-emitting diodes show which parts of the ventilation system are active, irrespective of whether the system is on automatic or under manual control.
To enable the system to achieve the required temperature in the cabin, data is required from a number of sensors, actuator motors, etc.
DESCRIPTION OF OPERATION
The climate control unit obtains data from both the control panel and the following sensors:
Cabin Temperature Sensor 218
Interior temperature sensor 218 is an NTC resistor which senses the temperature of the cabin air. It is integrated with suction fan 219, which provides an even air flow around the sensor. The sensor is connected via pins 15 and 33 while the suction fan is supplied with 12 V via pin 16.
Blended Air Temperature Sensor 217
The blended air temperature sensor is an NTC resistor which senses the temperature immediately after the air-mixing damper. The sensor is connected via pins 14 and 32.
Solar Sensor 223
The solar sensor consists of five solar cells arranged in a cube under the black cover. Pulses are sent to the solar sensor from ACC pin 5. Digital pulses are sent to pin 6 of the ACC control module via an amplifier stage.
Outside Temperature
The outside temperature is obtained in the form of digital pulses from EDU trip computer 210 applied to pin 18 of the ACC control module.
Power Supply
Climate control unit 216 is supplied with current via fuses 17 and 1.
The unit is always supplied with current directly from the battery via fuse 17. This is the main power supply for the system.
When the ignition switch is in the Drive position, the unit is also supplied with current via fuse 1. Suction fan 219 for interior temperature sensor 218 starts at the same time.
Ventilation fan 199 is supplied with current via fuse 6. Pin 31 of the unit is connected to instrument lighting rheostat 16.
Climate Control Unit 216
The unit controls the following functions/units:
^ Ventilation fan 36 via speed control 220. Fan speed is controlled steplessly. Pin 17 of the control module supplies the control with 12 V. A speed control voltage of 0-5 V is supplied via pin 20, where
0 V = fan stationary
5 V = maximum speed.
^ Stepping motor 222 for the air-mixing damper which controls the flow of air, directing it through the heat exchanger or bypassing it. The motor is connected to pins 27, 28, 30 and 29.
^ Stepping motor 221 for the air-mixing damper which controls the air flowing through the defroster and/or ventilation outlet. The motor is connected to pins 23, 24, 26 and 25.
^ Servo motor 38 for the air recirculation flap. When the flap is closed, air is admitted from outside and when it is open (recirculation position), air from inside the cabin is used (recirculated). The motor is connected to pins 2 and 21 of the unit.
^ Electrically heated rear window 115 and heating elements 207 in the door mirrors, which are controlled via relay 113. The relay is connected to pin 39.
^ Rear door fans 247RL and 247RR are connected to pins 9 and 10 respectively.
IMPORTANT: The cooling fins on the speed control are live (+12 V) when the ignition is switched on. If the cooling fins are grounded, the speed control will be rendered unserviceable.