If the refrigeration compressor crankcase is sweating or frosting and is operating with an unusual noise, what is most likely the cause?

Correct Answer: Option A — liquid refrigerant returning to the compressor

Liquid refrigerant migrating or returning to the compressor crankcase lowers oil temperature and boils off, causing heavy condensation or frost on the exterior shell. This liquid slugging creates severe mechanical knocking and unusual operating noises.