Uses electronic enlargement valve to exactly control the circulation of R290 refrigerant in the evaporator as well as a 4-way valve to divert the refrigerant circulation with the defrost Procedure Air source heat pumps use the same type of technologies that keeps a fridge or freezer amazing – but in https://purethermal.co.uk/media-news/q4-launch-lithium-large-capacity-r290-ashp-from-pure-thermal-and-enerblue/