A heating, ventilation, and air conditioning (HVAC) system for a vehicle may include: a casing having an inlet and a plurality of outlets; an evaporator disposed within the casing; a heater core disposed behind the evaporator within the casing; and an air mixing door disposed between the evaporator and the heater core. In particular, the heater core and a rear wall of the casing are spaced apart from each other by a first distance, the evaporator and the heater core are spaced apart from each other by a second distance, and the first distance is greater than the second distance.