The _________ must be insulated to decrease refrigerant temperature rise and exterior moisture condensation during the cooling mode of the refrigeration system.

In a refrigeration or air conditioning system, the vapor line (also known as the suction line) carries refrigerant vapor from the evaporator to the compressor. It must be insulated to prevent heat gain from the surrounding environment, which helps in maintaining a lower refrigerant temperature. Additionally, insulation helps to avoid exterior condensation, especially during the cooling mode. Condensation occurs because the vapor line can be cooler than the surrounding air, causing moisture to condense on the exterior of the line. Insulation prevents this, which is essential for efficient system operation.