Air humidity sensor, function - GF83.30-P-2125-01P

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The air humidity sensor (B31/2) measures the air humidity of the drawn in outside air to regulate air dehumidification.

The value of the air humidity sensor (B31/2) is passed on to the AAC [KLA] control and operating unit (N22) via the AC bus and is used to regulate the refrigerant compressor (A9) as well as the interior temperature.

As a result, air dehumidification can be reduced at low humidity, which facilitates a more pleasant climate in the vehicle interior.

The air around the evaporator is no longer cooled down to approx. 3 °C, as previously, in order to then be heated back up to the desired temperature (Reheat mode).

Reheat mode only takes place, if the reheat-associated air dehumidification effect is required to keep the windows condensation free when humidity is high. Three different regulation zones, which are dependent on the relative humidity, are defined as shown in the following tables.

The air humidity sensor (B31/2) operates in the following value ranges:

Relative humidity of intake air from 0 to 100 %
Temperature of inducted air from -40 to +85 °C
Dew point temperature from -40 to +85 °C

Relative air humidity	Operating condition
0 to 60 %	No reheat mode
40 to 90 %	Reheat mode with progressive temperature control between 0 °C and 12 °C
80 to 100 %	Full reheat mode