In the first stage, the refrigerant is suctioned into the compressor. The refrigerant is compressed, and become high temperature gas and then go into the condenser. The second stage, the high temperature gas state refrigerant condensed in the condenser. The condenser is normally in the outdoor. The heat is transited from refrigerant to the outdoor air. Refrigerant becomes medium temperature and high-pressure liquid in this stage. The third stage, the medium liquid state refrigerant goes through the expansion valve, the refrigerant becomes low temperature and low-pressure liquid. Finally, this liquid goes into the evaporator. Evaporator is normally in the indoor side of the air conditioners. The evaporation of refrigerant happens here, the heat of the room is transit from the indoor air to the refrigerant in the process of its evaporation. The refrigerant become low temperature gas in this stage and go to the compressor. This is a complete cycle. The cycle keeps running, and the air conditioner keep carrying the heat of room to the outdoor air. So, it keeps the room cool.

Do you know air conditioner can heat the room as well? A component called 4-way valve is added to the system. It can help reverse the flowing direction of refrigerant so as to reverse the function of evaporator and condenser. The refrigerant condensed in the evaporator, and evaporated in the condenser. In this way, the air conditioner can bring the heat from outdoor air to the room, and it can heat the room as well.