Humidity Sensor

The humidity sensor is located within the interior mirror and comprises 3 individual elements:

• A humidity sensor
• An air temperature sensor
• A windshield glass temperature sensor.

The readings from these 3 sensors combine to reduce the risk of misting on the windshield.

The humidity sensor element is contained behind a nylon mesh cover. The sensor comprises an element made up of film capacitors on different substrates. The dielectric is a polymer which absorbs or releases water proportional to the humidity of the air being drawn through the sensor. This causes a change in the capacitance of the sensor.

Humidity within the cabin is controlled by raising or lowering the temperature of the evaporator. An increase in evaporator temperature increases the moisture content of the air in the cabin. Lowering the evaporator temperature reduces the moisture content of the air in the cabin.

The capacitance of the sensor, together with both temperature values, is provided as LIN bus messages to the ATC module. The ATC module uses these signals to calculate the dew point of the air at the windshield. When the temperature of the windshield glass reaches or falls below this value, misting is likely to occur. In this instance, the ATC module will:

• raise the temperature of the air leaving the heater assembly
• adjust the position of the demist distribution motor
• adjust the position of the Recirculation motor
• reduce A/C compressor displacement
• power the windshield heater elements (if fitted).