Fan having a step diffuser

A fan, comprising:

• a housing with a cylindrical inner contour, wherein the housing and the cylindrical inner contour terminate at a housing outflow-side edge;
• an impeller arranged in the housing and rotationally driven by an electric motor, with blades extending between a hub ring and a cover ring, wherein the cover ring surrounds the blades;
• wherein the inner contour of the housing and a cover ring outflow-side edge of the cover ring define a step diffuser forming an abrupt expansion in a flow cross section formed downstream of the impeller between the cover ring outflow-side edge of the cover ring and the cylindrical inner contour of the housing in the flow direction, wherein a contour of the cover ring interacts with the cylindrical inner contour of the housing with respect to a main flow and a secondary flow through the fan and an imaginary extension of the contour of the cover ring does not intersect the cylindrical inner contour of the housing prior to the housing outflow side edge;
• and
• a guide device having a plurality of guide blades is arranged downstream of the impeller in the flow direction, wherein the guide device is configured to influence the flow in the region of the step diffuser.