The liquid line is the smaller of the two copper pipes in a refrigerant line set, carrying high-pressure liquid refrigerant from the condenser to the indoor unit. In cooling mode, this line is typically warm to the touch and does not require as much insulation as the larger suction line. However, protecting this line is still important for the overall efficiency of your heat pump condensers. Proper sizing of the liquid line is essential for the evaporator coils to receive the correct amount of refrigerant. You can find pre-flared liquid lines in our mrcool-accessories-1-4-1-3 and other line set collections. Ensuring both lines are properly handled is key to any diy-1 project.