Copper for various reasons

1. Thermal conductivity: the refrigerant flows through the coil, which transfers the heat of the room to the outdoor unit, where the refrigerant is cooled again to flow again through the evaporator and complete the next cycle of transfer. On the scale of thermal conductivity, copper ranks second, right after silver, while aluminum ranks fifth and other alloys perform much worse. The high thermal conductivity of copper helps to lower the room temperature much faster.
2. Power consumption: in an inverter AC, where the compressor can be operated at different speeds, power consumption is lower when the speed is low. The faster the heat transfer is completed, the sooner the compressor speed is lowered, resulting in low power consumption. If an alloy is used instead of copper, heat transfer is delayed, resulting in high power consumption.
3. Durability: Copper has a much higher density than aluminum or iron. Because of this higher density, the metal has a very high evaporation temperature, making it last longer in numerous condensation and evaporation processes.
4. Repairable: Leaks in copper tubing are easily repaired by soldering. If your technician’s visit is delayed, you can use a few layers of copper tape to achieve decent temperatures. With aluminum or another alloy, we may need to weld to repair leaks. The welding heat and melt can react with the refrigerant in a way that defeats its purpose, and so repairing leaks often involves refilling refrigerant, which actually costs more than repairing copper tubing.