Why Refrigeration Compressor Takes Suction from Crankcase?

Since crankcase is pressurized, no air can enter the system. No refrigerant gas is wasted by even small blow pasts from the compressor pistons. Refrigerant gas is miscible with oil. This property helps the gas to bring the oil in the system back to the compressor.

Why does refrigerant from evaporator enters the compressor through crankcase?

Because liquids and vapors flow from high- to low-pressure areas, the refrigerant will migrate to the crankcase, which is the lowest pressure point in a refrigeration system.

Does refrigerant migrate to crankcase in compressor?

Refrigerant migration occurs as a result of a difference in vapor pressure between the oil in the crankcase of the compressor and the refrigerant vapor in another part of the system. Normally, the refrigerant vapor migrates back from the system's evaporator through the suction line during the off cycle.