Cabin Temperature Sensor / Switch: Description and Operation

In year model 1985, the cabin sensor has a hose going to a separate fan.
From year model 1986-, the sensor has a built-in suction fan which sucks cabin air past an NTC resistor. NTC stands for Negative Thermal Coefficient and means that resistance decreases as temperature rises.

In year model 1995, the sensor is powered from pin 33 and grounded on pin 15 on the Automatic Climate Control (ACC) control module.

The suction fan is supplied with voltage from pin 16 on the ACC control module and is grounded to grounding point G8.

The cabin temperature is the ACC control module's most important measured value and is compared with the selected cabin temperature to decide if the blended-air temperature should be raised or lowered.

Cabin temperature is adjusted with reference to the outside temperature to achieve the physical sensation of the selected temperature. If the difference between the selected temperature and the adjusted cabin temperature increases, the speed of the ventilation fan will also increase.

As heat behind the facia affects the reading from the cabin temperature sensor during short stops, the ACC control module rechecks the reading 45 seconds after the engine has been started for year model M1995.

For the same reason, the sensor suction fan continues to suck air through the sensor for 20 - 50 seconds after the ignition has been switched off for year models 199094 and for 4 minutes for year model 1995-.
Both these features reduce the risk of erroneous data.

If there is no reading from the cabin temperature sensor, temperature 'is set at +18° C (64.5° F).