A method for upgrading an air conditioning system (40) for a vehicle (58) having a motor, wherein the air conditioning system (40) comprises an air guiding structure (8) configured to guide an air flow (34) generated by the air conditioning system (40). The method comprises the step of arranging an ultraviolet (UV) light source (4) in a position, in which the light source (4) emits UV light (36) irradiates the air flow (34).
