CSLB C-20 HVAC ContractorCooling and RefrigerationMedium
A technician installs a new condensing unit and ensures its crankcase heater is energized for 24 hours before the compressor is started. What is the primary purpose of a crankcase heater?
- ATo reduce head pressure during compressor startup
- BTo keep the compressor oil warmer than the surrounding refrigerant, preventing refrigerant migration and oil dilution during the off cycle
- CTo prevent frost from forming on the suction line
- DTo increase compressor cooling capacity during operation
Show answer & explanationAnswer & explanation
Correct answer: B. To keep the compressor oil warmer than the surrounding refrigerant, preventing refrigerant migration and oil dilution during the off cycle
During the off cycle, refrigerant can migrate to the cooler compressor crankcase and condense into the oil. A crankcase heater keeps the oil warmer than the surrounding refrigerant vapor, preventing this migration and reducing the risk of oil foaming and liquid slugging on startup.
Why the other options are wrong
- A. Head pressure is unrelated to crankcase heater function; it manages oil/refrigerant separation, not pressure.
- C. Frost prevention on the suction line is unrelated to the crankcase heater's purpose.
- D. Crankcase heaters do not affect cooling capacity; they protect the compressor during standby periods.
Crankcase Heater
An electric heating element wrapped around or inside a compressor crankcase that keeps oil warm during the off cycle to prevent refrigerant migration and startup damage.
- Prevents liquid refrigerant from mixing with oil during shutdown
- Reduces risk of oil foaming and compressor slugging on startup
- Should be energized for a period before initial startup or after extended power loss
Memory trick: Warm oil stays put — cold oil lets refrigerant loot.