In an oil safety switch for a refrigeration system, the oil pressure must always be above the ______ side pressure for oil to flow.

• A. High
• B. Low
• C. Medium
• D. Vacuum

Answer: (B)

Oil can flow only when the lubricating oil pressure is higher than the pressure on the low (suction) side of the system. The oil pump pushes oil through the lubrication paths and bearings, but it has to overcome the pressure on the low side for the oil to move toward the compressor and back to the sump. If the oil pressure drops below the low-side pressure, oil flow stops, risking the compressor’s lubrication. That’s why the oil safety switch is set to trip when oil pressure falls below the low-side pressure.