Body relaxation for air conditioning installation and valve unit used for this purpose

An expansion device for an air conditioning system, for example CO2 for motor vehicles, and a valve unit that can be used in particular for the latter, comprises a fixed restrictor 16 between a high pressure side of the valve, upstream, and a low pressure side of the valve, downstream. The expansion member 17 contains a control valve, which is biased by the refrigerant of the low pressure side or by a physical quantity related therewith, as a manipulated variable or a new type of valve unit . The valve unit includes a fixed throttle and at least one other valve component in the form of a pressure relief valve 27 disposed in a bypass line bypassing the fixed throttle or a regulating valve influencing section passage of the fixed restrictor.