A method for conditioning air in a temperature-insulated test space of a test chamber and a test chamber serving for receiving test material, in which a temperature ranging from −20° C. to +180° C. is generated within the test space. A cooling cycle has an internal heat exchanger, which is connected on a high-pressure side of the cooling cycle downstream of a gas cooler and upstream of an expansion valve, the internal heat exchanger being coupled with a medium-pressure bypass of the cooling cycle, the medium-pressure bypass being connected downstream of the internal heat exchanger or the gas cooler and upstream of the expansion valve on the high-pressure side as well as upstream of a high-pressure compressor and downstream of a low-pressure compressor on a medium-pressure side of the cooling cycle, refrigerant being dosed in the medium-pressure side from the high-pressure side via the internal heat exchanger by a second expansion valve.