Heating or air conditioning installation

The invention relates to a heating or air conditioning system for ventilating a passenger compartment with a climate box (10) in which a heat exchanger (11) is accommodated and at least one air mixing chamber (13, 14) is formed, which has an inlet opening (16) for warm air flowing through the heat exchanger and an inlet opening (17) for cold air flowing around the heat exchanger, as well as at least two outlet openings for ventilating the passenger compartment, and with an air mixing device (30) controlling the inlet openings. To ensure ventilation that is comfortable for the passenger in every operating mode of the system with minimal structural effort, a throttle member for throttling the opening cross-section is arranged at an outlet opening, whose actuation by the air mixing device takes place such that the outlet opening is maximally throttled when the warm air inlet opening is maximally released and is completely released when the cold air inlet opening is maximally released.