Final answer:
Crankcase heaters and automatic pump down cycles are used to prevent liquid refrigerant migration or slugging in refrigeration and heating systems, which can protect the compressor from damage.
Step-by-step explanation:
A crankcase heater and an automatic pump down cycle are utilized in refrigeration and heating systems to prevent liquid refrigerant migration or slugging. When a refrigeration system is not in operation, the cooler refrigerant may migrate to the oil in the compressor, which can then lead to compressor damage when the system restarts. The crankcase heater keeps the oil warm, preventing refrigerant migration. An automatic pump down cycle, on the other hand, operates to remove refrigerant from the evaporator and suction lines and store it in the receiver before the system shuts down, thereby protecting the compressor from potential damage caused by liquid slugging when it starts up again.