Humidity Sensor
The humidity sensor is installed in a bracket attached to the inside of the windshield close to the rear view mirror. The sensor is concealed under a cover, which clips onto the bracket.
The sensor comprises three individual elements:
- A capacitive humidity sensor
- A NTC thermistor, air temperature sensor
- An infrared windshield glass temperature sensor.
The humidity sensor has a power supply connection from the BCM/GWM assembly. The data from the three individual elements of the humidity sensor are transmitted in LIN bus messages to the HVAC.
The HVAC use these signals to control the following:
- Adjusts the humidity of the air in the vehicle as necessary, to provide the optimum comfort level for occupants.
- Calculates the dew point temperature of the air at the inside of the windshield.
Humidity within the vehicle is controlled by raising or lowering the temperature of the evaporator. An increase in evaporator temperature increases the moisture content of the air at the windshield. Lowering the evaporator temperature reduces the moisture content of the air in the interior.
If the dew point of the air within the passenger compartment rises to be close to that of the windshield, temperature misting is likely to occur.
To prevent this, the HVAC will:
- Increase the blower speed
- Reduce the evaporator operating temperature to its lowest safe running temperature
- Increase the temperature of the air leaving the climate control assembly
- Adjust the position of the demist distribution motor to direct more air to the windshield
- Adjust the position of the recirculation motor to admit more fresh air
- Send a message to the BCM/GWM assembly via the HS CAN comfort systems bus, to energize the windshield heater (if equipped).