Copeland 998-0002-04 Recharge Oil Sight Glass is a refrigeration and HVAC service component designed to monitor compressor oil levels during system operation and maintenance. It works by providing a clear viewing window that allows technicians to visually inspect the oil condition and level without disassembling the equipment. https://www.partshnc.com/998-0002-04-copeland-recharge-oil-sight-glass