Migration of refrigerant to the compressor’s crankcase during an off cycle is a serious problem. Significant compressor damage can occur if the problem is not remedied. If refrigerant migration does occur, an immediate drop in crankcase pressure will occur when the compressor starts. This will cause the refrigerant and oil mixture to explode violently and foam up through the cavities of the compressor and cause broken discharge valves and reeds.
The only sure remedy for compressor migration is an automatic pump down system. One must clear all refrigerant (liquid and vapor) from the evaporator and suction line before every off cycle. Automatic pump down is accomplished with a thermostat controlling a liquid-line solenoid in combination with a low-pressure controller terminating the on cycle once the evaporator and suction lines are void of any refrigerant. This will ensure that there is no refrigerant in the evaporator or suction line to migrate towards the compressor.