The refrigerant circuit forms the heart of every refrigeration and air-conditioning system. It consists of four main components: compressor, condenser, expansion valve, and evaporator. The refrigerant absorbs heat from the medium to be cooled in the evaporator and evaporates. The compressor increases the pressure and temperature of the vapour. In the condenser, the refrigerant releases heat to the surroundings and condenses. The expansion valve reduces the pressure before re-entry into the evaporator. Common refrigerants include HFCs such as R410A or R32, as well as natural refrigerants such as R290 (propane) or R744 (CO₂). The EU F-Gas Regulation governs the phase-down of high-GWP substances.