A vehicular air conditioning system provided with a cooling heat exchanger and a heating heat exchanger includes a cold air flow path through which an air passing through the cooling heat exchanger bypasses the heating heat exchanger, a hot air flow path through which the air passing through the cooling heat exchanger passes, a plurality of temperature doors configured to allow the air passing through the cooling heat exchanger to selectively pass through the heating heat exchanger, and an interlocking part configured to allow the temperature doors to be driven in conjunction with each other.