A heater that keeps compressor oil warm so refrigerant does not migrate into it during the off cycle.
Refrigerant migrates to the coldest part of a system when it is off and dissolves into the compressor oil. At start-up the pressure drop makes it boil violently, foaming the oil out of the crankcase. A crankcase heater keeps the oil warmer than the rest of the system to prevent that. Many manufacturers require the heater to be energized for a set time before first start.
Exam work areas
E · Commissioning and start-up