Commercial Refrigeration II Practice Exam

To safely isolate a semihermetic compressor from system pressure, you need to block all paths that could push refrigerant pressure into or out of the compressor. Front-seating the suction and discharge service valves does this by sealing off both sides of the compressor at the valve seats. With both valves front-seated, there is no pressure path from the system into the compressor, and the compressor can be serviced without the risk of refrigerant release or pressure on internal components. Opening the valves fully would reintroduce system pressure to the compressor, and closing only the charging port or removing the service manifold does not reliably isolate the compressor from both the suction and discharge paths. Front-seating both service valves is the proper, safe way to achieve complete isolation.