In a split system air-conditioning unit, what is the small line referred to?

The small line in a split system air-conditioning unit is known as the suction line. This line carries refrigerant vapor back to the compressor after it has absorbed heat from the indoor air. It typically has a larger diameter than the liquid line and is insulated to prevent heat gain. This line is crucial for the operation of the system, as it helps maintain the proper flow of refrigerant throughout the cycle, ensuring efficient cooling.

In a split system, the refrigerant circulates between the indoor and outdoor units through both the suction line and the liquid line, which is larger in diameter and carries the high-pressure liquid refrigerant from the outdoor unit to the indoor coil. The vapor return and liquid supply are essential components of the vapor-compression refrigeration cycle, where the refrigerant transitions between liquid and vapor states to facilitate heat exchange. Understanding the distinction between these lines is critical for diagnosing and servicing in HVAC systems.