Abstract: An air conditioning system for motor vehicles having a flat roof construction for installation of the air conditioning system on the roof, is presented. The air conditioner comprising a condenser unit accommodated in a housing part and an evaporator unit accommodated in another housing part, wherein one of these two units in the direction of travel is mounted substantially in line behind the other of the two units. The evaporator unit has an inside housing part in which a circulating air opening from the passenger compartment opens out, through which the air from the passenger compartment via evaporator registers and/or heating registers which extend substantially parallel to the direction of travel, as well as via a blower arrangement can be fed back into the passenger compartment. The evaporator unit lies in the direction of travel in front of the condenser unit and in the front face of its housing part has a fresh air inlet opening that can be closed off.