If the refrigerant suction line rises vertically from the compressor, a trap must be installed at the ______ of the riser.

• A. Top
• B. Middle
• C. End
• D. Bottom

Answer: (D)

When a suction line rises vertically, gravity makes any liquid or oil that forms in the line want to settle at the lowest point. Placing an oil/liquid trap at the bottom of the riser captures that liquid at its lowest point and provides a path for it to drain back, helping keep the compressor suction gas dry and preventing liquid slugging or oil migration up the line. If the trap were higher up or at the top, liquid would not be reliably collected and could ride up into the compressor, which is undesirable. Therefore, the trap is installed at the bottom of the riser.