Device for detecting risk of misting of a vehicle window and installation having such a device

The detector for fogging of a motor vehicle windscreen uses values of the average surface temperature (Tr) of the screen (Tv) and a dew point temperature (Tr) for the air in the passenger space. Comparison of the two temperatures is representative of the risk of fogging of the screen. A computer estimates the comparison between the screen and dew temperatures and delivers a risk value signal. The signal can be fed to an air conditioning control. The computer can have a memory for storing the values. Claims include a ventilation system for the vehicles using the detector