The present invention relates to a method for operating a vehicle air-conditioning system (3) having a refrigeration circuit (13), in which a refrigerant circulates, and having an evaporator (14) for cooling an air flow (12), and to a thermoelectric heating device (18) for heating the air flow (12), the heating device (18) and the evaporator (14) being situated in a duct (11) leading into the vehicle interior (2). The refrigerant circuit (13) is activated in order to cool the vehicle interior (2). In order to improve comfort conditions by a perceptibly rapid response of the interior cooling system, the heating device (18) is operated as a cooler during a start-up phase of the refrigerant circuit (13), such that the heating device (18) extracts heat from the air flow (12).