An air conditioner for a vehicle includes a heating line having a condenser at an inlet thereof and having an outlet communicating with an interior of the vehicle. A cooling line has an inlet communicating with the inlet of the heating line, an outlet communicating with the interior of the vehicle, and an evaporator connected to the condenser inside of the cooling line. One or more doors are provided to control a flow stream of each line and to control a temperature of air introduced into the interior of the vehicle.