Heat pump system for a vehicle

A heat pump system for a vehicle, the heat pump system comprising:

• an air conditioner unit comprising a compressor, a first heat-exchanger, a second heat-exchanger, a first expansion valve, and a third heat-exchanger that are connected through a refrigerant line to circulate a refrigerant through the refrigerant line;
• and
• a chiller connected to the refrigerant line through a first connection line, and configured to adjust the temperature of a coolant by heat-exchanging the refrigerant supplied from the air conditioner unit with the coolant,
• wherein the air conditioner unit further comprises:
• a first valve provided in the refrigerant line between the first heat-exchanger and the second heat-exchanger;
• a second valve provided in the refrigerant line between the third heat-exchanger and the compressor;
• a second expansion valve provided in the first connection line;
• a second connection line having a first end connected to the refrigerant line between the first heat-exchanger and the second heat-exchanger, and a second end connected to the refrigerant line between the second heat-exchanger and the third heat-exchanger;
• and
• a third expansion valve provided in the second connection line.