Abstract: A system for removing lubricating oil from a refrigeration system the lubricating oil being used together with a first type of refrigerant in said system and replacing this oil with an oil which is compatible with a second type of refrigerant, to convert the refrigerating system or heat pump system from a system which operates with said second type of refrigerant, by flushing the system to be cleansed of oil with a circulating refrigerant of the first type. The refrigerant is capable of dissolving the oil and has a higher density than said oil so as to be able to lift and entrain the oil during the flushing process. The refrigerant is circulated through the entire refrigeration system and through an external apparatus used to circulate the refrigerant.