Final answer:
The crankcase heater in an HVAC system prevents refrigerant migration by keeping the crankcase warm, which helps reduce compressor wear.
Step-by-step explanation:
The primary purpose of the crankcase heater during the off cycle in an HVAC system is to prevent refrigerant migration (a). Refrigerant migration can lead to several issues, including refrigerant condensing in the compressor’s oil during periods of inactivity, which may wash the lubricant from the bearings and cause increased wear on startup. By keeping the crankcase warm, the heater ensures that the refrigerant remains in the vapor phase, decreasing the possibility of it mixing with the oil and thus reducing compressor wear over time.