Device for thermal treatment of air for a vehicle with improved temperature management

An air thermal treatment device for a vehicle, comprising a casing including a conveying duct, a heating duct and a mixing chamber which are formed by walls of the casing and are configured to place at least one air inlet opening of the casing and at least one air outlet opening of the casing in aeraulic communication, the conveying duct extending from the at least one inlet opening to the mixing chamber, the heating duct extending parallel to the conveying duct as far as the mixing chamber, the air thermal treatment device further comprising a mixing device configured to be movable between a first end position which prevents the circulation of air between the conveying duct and the mixing chamber, such that the air is intended to circulate in the heating duct, and a second end position which prevents air from circulating in the heating duct, the mixing device including a main flap adapted to be rotatable about an axis of rotation, wherein the mixing device further includes a deflection element protruding from an upper face of said main flap, the deflection element including at least one front rib lying in a plane including the axis of rotation and at least one lateral rib extending one end of the at least one front rib and lying in a plane perpendicular to the axis of rotation.