Carrier HT31AZ241 Crankcase Heater L99H008 this specific model requires a this specific model requires a 230V 3 phase power supply The silver dot is typically located on the face or side of the limit switch body to designate the specifically calibrated 240 degree trip point used in Reznor factory specifications Compatible with Carrier 5H series compressors and compatible HVAC R equipment Standard technical protocols for 5H compressors require the crankcase heater to be energized for at least 24 hours prior to initial startup or after long periods of inactivity to ensure all migrated refrigerant has boiled off from the oil