Today's passenger cars are equipped with large window areas, allowing penetration of solar radiation and build up of heat inside the compartment. Optimum air conditioning which is primarily regulated by the dashboard louvers is therefore an important factor as far as the temperature in the upper level of the compartment is concerned. Theoretically, an air conditioning unit having a variety of control settings offers an optimum level of temperature comfort under any weather conditions, however, improper control setting is very often the cause of unpleasant temperature conditions. If cold air is blown out directly through the dashboard louvers the temperature can be regulated for either side and errors in control setting can be avoided. Regulation of temperature in air conditioning units which offer only manual setting is achieved mostly by blended air and very often the dashboard louvers are supplied with temperature-treated air, thus improving the comfort level under any weather conditions.