Refrigerant Migration:
Occurs during the off cycle when the compressor shuts off.
Refrigerant vapor migrates to the compressor oil in the crankcase due to vapor pressure differences.
Vapor condenses into liquid refrigerant below the oil in the crankcase.
Flooded Starts:
When the compressor starts, pressure reduction causes the liquid refrigerant to explode out of the oil.
This can wipe oil from the low bearing surface, causing significant damage:
Oil foaming
Poor lubrication
Possible slugging
Random pattern of damage on the crankshaft and lower connecting rods indicates a flooded start.
Prevention Measures:
Crankcase Heater: Heats the oil to prevent refrigerant condensation.
Automatic Pump Down Cycle: More effective; evacuates refrigerant from the low side during the off cycle and stores it in the high side.
Systems requiring protection:
Compressors in environments below 60°F
Systems with large refrigerant charges
Systems with long off cycles
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