What is the purpose of a crankcase heater and when should it be energized?

• A. To cool the compressor during start.
• B. To increase refrigerant charge.
• C. To protect from flash gas by preheating.
• D. Prevents refrigerant migration into crankcase and keeps oil warm; energize during startup in cold ambient conditions or per manufacturer.

Answer: (D)

The crankcase heater’s job is to prevent refrigerant from migrating into the crankcase and to keep the compressor oil warm so lubrication stays effective, especially at startup. In cold conditions, refrigerant can condense inside the crankcase and migrate into the oil, diluting it and making startup lubrication less reliable. By energizing the heater during startup (or during cold ambient conditions, per the manufacturer's guidance), the crankcase is warmed, which reduces condensation, keeps oil viscosity in a safe range, and minimizes the formation of flash gas when the compressor starts. This combination protects the compressor and improves startup reliability.

The other options don’t fit because the heater does not cool the compressor or increase the refrigerant charge. While preheating can influence gas behavior, the primary purpose is preventing refrigerant migration and keeping oil warm, with energizing tied to startup in cold conditions or per manufacturer.