ActronAir Crankcase Heater 90W (Metal) maintains compressor oil temperature during off-cycle periods on large-capacity Classic Series and ESP Plus residential split ducted systems, preventing refrigerant from migrating into the compressor sump and diluting the oil -- which causes bearing damage and premature compressor failure on the first start after a cold soak. Compressors on systems operating in warm climates where compressor off-time is limited may not require a crankcase heater -- consult the system installation guide before fitting. Isolate power at mains before replacing any crankcase heater components.