HEAT PUMP SYSTEM FOR A VEHICLE

A heat pump system for a vehicle is provided to improve cooling and heating performance by applying a gas injection device selectively operating in an air conditioning mode of vehicle interior to increase the flow rate of the refrigerant. The heat pump system includes a compressor, an HVAC module, an external heat-exchanger, a first expansion valve, an accumulator, a first connection line, a chiller, a second expansion valve, a gas injection device, and a second connection line, where a flow direction of the refrigerant is controlled depending on at least one mode for a temperature control of a vehicle interior.