167.Refrigeration migration

Refrigerant migration is defined as refrigerant, either liquid or vapor, traveling to the compressor’s suction line or crankcase during the off cycle. During the off cycle, or especially during a long shutdown, refrigerant will want to travel, or migrate, to a place where the pressure is the lowest.

If refrigerant migration does occur, and the crankcase is lucky enough to have a crankcase heater, the vapor will be forced away from the crankcase and end up in the suction line. This refrigerant may condense in the suction line and cause slugging in the compressor’s cylinders on start-up. Slugging is liquid refrigerant or liquid oil actually trying to be compressed in the cylinders of the compressor. Slugging happens during the compressor’s on-cycle. As we know, liquids cannot be compressed, and tremendous reversal forces are generated often resulting in broken parts. Slugging can especially happen if the compressor is located in a cold ambient outdoor setting. The cold ambient will amplify the lower vapor pressure area and help condense the refrigerant vapor to liquid. The crankcase heater does help keep the oil in the crankcase free of refrigerant from refrigerant migration.