Temperature Control

Operation
The automatic air conditioning regulates the temperature inside the car by controlling the air flow side of the system. Air temperature variation and regulation is undertaken by a control unit according to the preselected temperature (at the knurled temperature wheel), the prevalent temperature inside the car (internal sensor) and the outside temperature (external sensor).

The control unit's input signal for temperature regulation is the resistance in Ohms of this linked sensor circuit. The sensors have varying ratings, that is to say for a given temperature they make a different contribution to the output signal variations which are supplied to the control unit.

The internal sensor is on the control panel, behind a perforated panel. It consists of an NTC (negative temperature coefficient) and parallel resistor, and receives air from an airflow pump.

The internal sensor's resistance varies by 72 Ohms per degree Centigrade. To ensure uniform regulation, the resistor is designed to be slow-acting, and needs approximately 30 seconds to settle to a new value. The sensor is positioned on the facia to avoid an incorrect response caused by the sun striking the facia.

The external sensor is in the air duct box leading to the fan, and is attached to the left half-shell. It consists of an NTC, parallel and additional series resistor. The external sensor responds to outside (ambient temperature and alters its resistance by 17 Ohms per degree Centigrade. As a protective measure, the complete sensor is immersed in a protective lacquer before installation.

The knurled temperature control wheel is used to program the desired inside temperature in advance. There is no automatic temperature control at the two extreme limits of the selector range (16°C and 32°C/61°F and 90°F). At these settings the system provides maximum cooling or heating as the case may be. The temperature control wheel can be reset if out of adjustment by means of the screw between the two wheels.


The control unit contains the control and regulating components for the integral heating, ventilation and air conditioning system.

For control of the actuators (e.g. for ventilation, the water valve etc.) the unit contains electrical switches which are operated according to the control setting (lever on control unit).

The control unit regulates the interior temperature of the car by causing electric motors to vary the setting of the temperature mixing flap. The 0 - 100 % control range is equivalent to a 700 Ohm input signal variation.

The control unit is located on the left of the heating and air conditioning assembly.

The complete control unit is protected against electrical overloads by a flying (in-line) fuse at the right of the heater and air conditioning assembly. This fuse is accessible from the glove box.

The fuse is of 5 Amp miniature pattern.