What is the purpose of the crankcase heater on an AC compressor?

• A. To heat the room
• B. To increase compressor efficiency
• C. To boil off liquid refrigerant trapped in the oil
• D. To prevent refrigerant leak

Answer: (C)

The crankcase heater keeps the oil in the compressor warm so any refrigerant that has condensed or migrated into the crankcase can boil off and return to the system as vapor before startup. If liquid refrigerant remains in the oil when the compressor starts, it can cause hydraulic lock or poor lubrication, leading to damaged bearings and hard starting. By heating the crankcase during off cycles, the trapped liquid is evaporated, protecting the compressor and ensuring smooth startup. This function is not about heating the room, improving efficiency, or preventing leaks—the heater’s purpose is specifically to manage refrigerant in the oil and prevent startup damage.