General
GeneralSome cars are equipped with Automatic Climate Control (ACC). The heating and ventilation system is then controlled automatically, so that the required temperature will be maintained in the interior of the car, regardless of the ambient temperature. The system always includes an air conditioner (AC) with recirculation facilities.
This description deals only with the electrical function of the ACC system and is thus a supplement to Group 8, Body, in the Service Manual. The method of using the ACC is also described in more detail in the Service Manual.
In the ACC system, the manual control panel and the AC and recirculation buttons have been replaced by a microprocessor-controlled climate control unit. In addition, all dampers are actuated by servo-motors.
On starting, the system is set to AUTO and will then be controlled by a program stored in the microprocessor of the unit, so that the preset temperature will be maintained. The electric heating element for the rear window and the heating elements for the outer rear- view mirrors are also controlled automatically. The AC compressor can be disengaged by depressing the ECON button, although the other functions will still be automatically controlled.
A function can be selected manually by depressing the corresponding button on the right-hand side of the unit. If the button is depressed again. automatic control of the function will be resumed.
Regardless of whether the system is on automatic operation or whether it is controlled manually, LEDs will indicate which parts of the ventilation system are in operation.
Components of the ACC system
To enable the system to maintain the required climate in the interior of the car, it must be supplied with information from a number of transmitters, damper actuating motors, etc. (See figure below.)
The operation of the system is described under the following three headings:
- Transmitters
- Damper actuating motors and electric heater for the rear window
- AC compressor and radiator fans
Fault-tracing hints
To avoid damage to the climate control unit, the following actions must always be taken before any work is started on the ACC system:
- Disconnect the earth cable from the battery. Note that all information stored in the climate control unit concerning the preset temperature will be lost as soon as the cable is disconnected. On restarting, it will set itself to the AUTO mode, and a temperature will be selected at random.
- Disconnect the 25-pole connector before carrying out any measurements and fault tracing. Carry out all measurements at the connector and not at the climate control unit. Apart from replacement of the scale illumination, no work must be: carried out on the climate control unit.
Fault-tracing and monitoring program
The microprocessor of the climate control unit includes a special fault-tracing and monitoring program.
During operation, the program checks certain functions at regular intervals. The buttons on the unit can be used for starting the fault-tracing program, which will then check the transmitters, run the servo-motors, etc.
The following units are monitored during normal operation:
- Interior temperature transmitter 218
- Outdoor temperature transmitter 197
- Air-mixing transmitter 217
If a fault is detected on any of these transmitters, an emergency program will be switched in.
Fault-tracing program
During fault tracing, the microprocessor runs a built-in fault-tracing program to check the transmitters and damper motors. The number of faults and a fault code for each fault will then be presented on the display of the climate control unit.
The following fault types will be indicated: Certain open-circuits in the wiring, short-circuits, faults in certain components, motor blocking and wrong direction of rotation.
For open-circuits and short circuits, no indication is given as to whether the fault lies in the component or in the wiring.
Example: If fault code 2U is displayed, indicating open-circuit in the outdoor temperature transmitter, the connector, wiring and transmitter must all be checked.
Proceed as follows for fault-tracing:
Depress AUTO and VENT simultaneously. Then release the buttons.
The microprocessor will then run the fault-tracing program, which takes about 40 seconds. When it has run through the program, the number of faults will be shown on the display.
Then depress VENT once, and the first fault code will be displayed. When VENT is depressed again, the next fault code will be shown, etc.
Other fault-tracing
1. Check the relevant fuses and check that the supplies to them are live.
2. Check the relevant earth connections.
3. Check that the connectors are making satisfactory contact. Check also the connector for the climate control unit. Clean the contact surfaces by disconnecting and then reconnecting the connectors.
The suction fan of the interior temperature transmitter can be checked by allowing a piece of thin paper to be drawn against its inlet.
For particulars of checking the AC compressor and the radiator fans, see the section entitled "Air conditioner (AC)". The fault-tracing instructions are valid, except that fuse 6 is not involved.
Resistance readings:
Outdoor temp. transmitter ±0°C: 794.8-832.2 ohm
±25°C: 980-1020 ohm
Air-mixing transmitter Cold engine: 2-17 kohm
Warm engine: 0.79-2 kohm
Interior temp. transmitter ±0°C: 32.5-37.7 kohm
+20°C: 12.0-13.4 kohm
+25°C: 9.5-10.5 kohm