A blower unit for a heating, ventilation, and air conditioner system (HVAC) of a vehicle. The blower unit includes an inside/outside air switching box. A switching door disposed in the inside/outside air switching box that is configured to selectively open and close an inside air introduction port and an outside air introduction port of the inside/outside air switching box. A fan is also located inside the inside/outside air switching box and blows air introduced into the inside/outside air switching box from the inside air introduction port and the outside air introduction port into the passenger compartment. A first plurality of ribs is provided on an inner surface of the switching door with a first perforated panel coupled to each of the first plurality of ribs. The first plurality of ribs and the first perforated panel reduce noise generated during an inside air introduction mode.