A device for heating and/or air conditioning for a motor vehicle comprising an air inlet for feeding air; an air transmission branch and an air heating branch , both fed by the air inlet and communicating with each other through a mixing zone ; and mixing means configured to distribute an air flow between the air transmission branch and the air heating branch , wherein said mixing means are movable between two extreme positions comprising a closed position, wherein the mixing means prevent a communication between the air inlet and the air heating branch and force the air flow to flow through the air transmission branch ; and an open position, wherein the mixing means prevent communication between the air inlet and the air transmission branch , and force the air flow to flow through the air heating branch ; wherein said mixing means comprise a tilting flap arranged between the air inlet and the air transmission and air heating branches , said tilting flap comprising a first end hinged to a sliding transmission element configured to drive the tilting flap , and a second end guided by a sliding guide configured to orient the tilting flap relative to the air flow, wherein in said closed position the tilting flap closes an inlet of the air heating branch and deflects the air flow into the air transmission branch , and in said open position the tilting flap closes an inlet of the air transmission branch and deflects the air flow into the air heating branch , the device being characterized in that in said closed position the first end of the tilting flap is in abutment against a first wall of the air inlet , and the second end of the tilting flap is in abutment against an inner partition separating the air heating branch from the air transmission branch , and in said open position the first end of the tilting flap is in abutment against a second wall of the air inlet , opposite to said first wall , and the second end of the tilting flap is in abutment against said inner partition . wherein said mixing means comprise a tilting flap arranged between the air inlet and the air transmission and air heating branches , said tilting flap comprising a first end hinged to a sliding transmission element configured to drive the tilting flap , and a second end guided by a sliding guide configured to orient the tilting flap relative to the air flow, wherein in said closed position the tilting flap closes an inlet of the air heating branch and deflects the air flow into the air transmission branch , and in said open position the tilting flap closes an inlet of the air transmission branch and deflects the air flow into the air heating branch , the device being characterized in that in said closed position the first end of the tilting flap is in abutment against a first wall of the air inlet , and the second end of the tilting flap is in abutment against an inner partition separating the air heating branch from the air transmission branch , and in said open position the first end of the tilting flap is in abutment against a second wall of the air inlet , opposite to said first wall , and the second end of the tilting flap is in abutment against said inner partition . <EOS>