Heating or air conditioning unit

A unit for conditioning air in a motor vehicle, comprising:

• a housing with at least one receptacle;
• at least one of a heater and an evaporator supported in the housing;
• an inlet opening for receiving air;
• an outlet opening for discharging conditioned air;
• at least one duct arranged between the inlet and outlet openings;
• at least one air control element for regulating air flow through the at least one duct, the at least one air control element including an installation frame supporting a plurality of louvers;
• and
• the installation frame comprising at least one frame side having a profile for positive-locking engagement with respect to the housing receptacle.