The correct answer is A) you must first remove the stem seal cap. When opening or closing compressor service and line isolation valves on a typical refrigeration system that is fitted with packed valves, you must first remove the stem seal cap. This allows access to the packing gland, which must be loosened to avoid excessive friction and wear on the valve stem as it is turned. Loosening the packing gland is necessary to ensure the valve can be operated smoothly and without damage. The other answer choices are incorrect because: B) replacing the gasket each time is unnecessary, C) you should not avoid loosening the packing gland, and D) turning the valves slowly is good practice but not the primary concern when opening or closing these types of valves.