Abstract: A heating and ventilation unit for a motor vehicle comprises a mixing chamber containing a heat exchanger and disposed within the vehicle interior. Pipe connections extending from the heat exchanger pass through the rear wall of the mixing chamber. An aperture in a wall of the mixing chamber is provided for enabling the heat exchanger to be withdrawn from the mixing chamber into the vehicle interior. The aperture is formed in a side wall of the chamber and is dimensioned to permit passage of the heat exchanger as well as the rearwardly projecting connections. A closure and support element is provided which is insertable through the aperture and which, when inserted, serves to support the heat exchanger within the chamber and prevent forward displacement of the exchanger away from the rear wall of the mixing chamber.