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 B — liquid refrigerant returning to the compressor

Liquid refrigerant returning down the suction line into the crankcase boils off the lubricating oil and chills the compressor body. This phenomenon, known as liquid slugging or floodback, causes severe mechanical knocking noises and exterior frosting.