The Breezaire 4SM21C Sight Glass is a crucial component in WKSL models, designed to provide a visual indicator of the refrigerant flow and system charge. It allows users to monitor the refrigerant level within the cooling system, helping to ensure that the system is properly charged for optimal performance. By providing a clear view of the refrigerant status, the sight glass helps prevent potential issues caused by low or high refrigerant levels, which can affect the cooling efficiency and longevity of the system. Regular inspection of the sight glass is essential for maintaining the efficiency and reliability of the unit, ensuring that the wine storage environment stays consistent and properly controlled.