A constructional unit for a heat exchanging device that includes at least one housing in which a gaseous medium is at least partially guided on a predetermined path, an inlet device for the gaseous medium, at least one first heat exchanging device, at least one second heat exchanging device, at least one controller that influences the direction of flow of the gaseous medium in at least some sections and that can be adjusted to at least two different positions, and an outlet device for the gaseous medium. In at least one first position of the first controller, substantially no portions of the gaseous medium are guided through the first heat exchanging device.