When a refrigerator unit is removed, inner surfaces of a refrigeration unit housing extending into a cryogenically cooled system are heated. The method is performed in such a way as to prevent the external atmosphere from coming in contact with the housing inner surfaces, thus avoiding the problem of ice formation within the housing. A heat gun is used in conjunction with an apparatus which fits into the housing and distributes heated gas, such as nitrogen, from the heat gun to different parts of the housing in relative quantities. The inner surfaces are brought to the same temperature in the same time allowing the housing to be cleaned before the refrigeration unit is replaced. The apparatus guiding the heated gas is mounted on the outside of the housing and includes stops on its supports to keep the apparatus from making contact with the inner surfaces of the housing. Spring loaded temperature sensors attach to the apparatus at different points and make contact with the inner end surfaces of the housing, allowing the housing temperature to be monitored during the heating process.