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Refrigeration & Air Conditioning Mechanic Red Seal · Question

In a refrigeration system with a vertical suction riser, what is the purpose of installing a P-trap at the bottom of the riser?

A P-trap at the bottom of a vertical suction riser is designed to collect compressor oil and ensure it is carried up the riser by the velocity of the refrigeran

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Question: In a refrigeration system with a vertical suction riser, what is the purpose of installing a P-trap at the bottom of the riser?

Answer options:

  • To collect and return refrigerant liquid to the compressor ✅ To prevent lubricant from draining back into the evaporator during off-cycles
  • To reduce noise transmission from the compressor
  • To isolate the compressor from evaporator vibrations

Correct answer: To prevent lubricant from draining back into the evaporator during off-cycles

Explanation: A P-trap at the bottom of a vertical suction riser is designed to collect compressor oil and ensure it is carried up the riser by the velocity of the refrigerant gas flow, preventing oil from draining back into the evaporator coil during off-cycles and potentially causing oil logging, which impairs heat transfer.

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