ActronAir Crankcase Heater 30W (Metal) maintains compressor oil temperature during off-cycle periods on small-to-mid 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. The 30W rating is the most common crankcase heater in the ActronAir range, suited to the majority of residential split ducted compressors. Isolate power at mains before replacing any crankcase heater components.