In order to efficiently perform heating of a vehicle interior in a state in which the external temperature is low and heat generated by a heating element is not sufficient in an early stage of driving the vehicle, a heat pump system for a vehicle is provided. The heat pump system utilizes various heat sources in a general heating mode of the vehicle interior, and at the same time, maximizes the system performance by increasing flow of the refrigerant. The heat pump system may include: a compressor, a heating, ventilating, and air conditioning (HVAC) module; a heat-exchanger; a first expansion valve; a first connection line; a chiller; a second expansion valve; a second connection line; a third connection line; and a fourth connection line.

A vehicular air conditioner includes a console duct and a rear floor duct configured to blow air discharged from a front seat blower to a rear seat passenger side and a rear floor side, respectively, a rear seat mode door configured to control air distribution from the front seat blower to the console duct and the rear floor duct, a rear seat blower installed in the console duct so as to increase an air flow rate and air pressure of the air blown to the rear seat passenger side, a rear seat console door installed in an internal passage of the console duct so as to adjust the air flow rate of air blown to the rear seat passenger side along the console duct, and a control part configured to control an opening position of the rear seat console door with respect to the console duct.