When opening or closing compressor service and line isolation valves on a typical refrigeration system that is fitted with packed valves, what must you do?

Correct Answer: Option C — you must first remove the stem seal cap

Packed marine compressor service and isolation valves feature an external stem seal and packing gland. To prevent refrigerant leakage past the valve stem during manipulation, technicians must first remove the brass stem seal cap before operating the valve stem.