The liquid line is the smaller of the two copper pipes in a mini-split Line Set. It carries the high-pressure liquid refrigerant from the outdoor Central Condenser to the indoor unit. In our standard Installation Kits, this is typically the 1/4" or 3/8" diameter pipe. It is usually insulated to prevent heat gain and to ensure the refrigeration cycle remains efficient. When installing a Multi-Zone system, each indoor head will have its own dedicated liquid line. Proper flaring and torqueing of this line are essential to prevent leaks. You can find the exact line sizes for your model in the Technical Data section. This line is a vital half of the "loop" that keeps your home cool.