R134a (1,1,1,2-Tetrafluoroethane) is the refrigerant. It is a gas.
Every compressor also needs lubricating oil.
What Type Of Refrigerant Oil Is Used In R134A Systems?
Either PAG =polyalkylene glycol
Or PAO = Polyalphaolefin
Or POE =
Polyolester Oil - this is the one used in our cars.
Traditionally PAG oils were mixed with a fluorescent contrast agent for UV leak detection.
The POE oils used for electric vehicles do not have this UV leak detection.
(Although new brands are now coming on to the market :-
uv-dye-for-electric-vehicle
Now look at the Kia Soul EV manual :-
refrigerant_direction_control_valve_repair_procedures
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The transition from R134A refrigerant to R-1234yf is about the Global Warming Potential. It has nothing to do with the transition from ICE vehicles to EVs.
Following the Montreal Protocol in 1996 that eliminated CFCs because of their Ozone Depleting Potential, the Kigali Amendment was created in October of 2016 to phase down hydrofluorocarbons (HFCs) like R-134A because of its high Global Warming potential (GWP).
The latest EPA regulations require new vehicles offered for sale (starting in the 2021 model year) to use a refrigerant other than R134a.