What is the role of an oil separator in an ammonia refrigeration system?

• A. It absorbs moisture from the system oil.
• B. It filters solid particulates from the liquid refrigerant.
• C. It cools the refrigerant before compression.
• D. It removes oil from refrigerant vapor and returns it to the compressor.

Answer: (D)

Oil separators in an ammonia refrigeration system are there to remove entrained lubricant from the refrigerant vapor and return that oil to the compressor. As the refrigerant vapor leaves the evaporator, it often carries oil shed from the compressor. If this oil rides along with the vapor all the way to the condenser, into the receiver, or back to the compressor, lubrication can be compromised and oil can be carried into parts of the system where it isn’t wanted. The separator provides a chamber where the vapor slows, oil droplets coalesce, and the accumulated oil drains back to the compressor crankcase or oil sump through a dedicated return line. This keeps the compressor properly lubricated, minimizes oil carryover with the refrigerant, and helps maintain efficient heat transfer and overall system reliability.

Absorbing moisture from system oil would be moisture control, not oil separation. Filtering solid particulates from liquid refrigerant describes a filter for liquid line contaminants, not oil in the vapor. Cooling the refrigerant before compression is the job of the condenser or intercooler, not the oil separator.