A mixer, which forms the core part of an air-conditioning assembly of a rail vehicle, has two inlets, an outlet, and a central region between the inlets and the outlet. A first inlet is connected to a fresh air supply, and a second inlet is connected to a circulating air supply such that fresh air and circulating air reach the central region, where the circulating air is mixed with the fresh air to obtain supply air. The central region is connected to the fresh air inlet via an opening, which forms a transition region between the fresh air inlet and the central region. The transition region contains a profiled section with a wing-shaped cross-section in the transition region where the supplied fresh air generates negative pressure along the transition region, and the circulating air is suctioned into the central region of the mixer with a boost from the negative pressure.