A vehicle air conditioning system is provided and includes a heating duct through which internal air and external air are introduced and a cooling duct through which internal air and external air are introduced. A condenser is disposed in the heating duct and an evaporator is disposed in the cooling duct and is connected to the condenser. A phase change material (PCM) stores thermal energy of the internal air passing through the heating and cooling ducts. An internal/external air door controls the mixing of the internal/external air introduced into the heating and cooling ducts, and a PMC door controls the external air introduced through the heating and cooling ducts whether to pass through the PCM.