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 D — liquid refrigerant returning to the compressor

Frosting or sweating of the compressor crankcase coupled with unusual mechanical noise indicates liquid slugging. Liquid refrigerant is returning through the suction line, boiling off in the crankcase, washing away lubricating oil, and threatening catastrophic compressor valve or mechanical failure.