offgridQLD wrote: The gas would only need to be replaced if it leaks out. Same as a refrigerator or home Airconditioner this shouldn't need doing and can hold tight for decades.
Though the week link in a automotive AC units on a ice car is the rubber flex lines from the compressor to the engine bay hard lines. They are more or less unavoidable due to the twisting vibrating engine.
I can't remember last time I looked at the Imiev AC system but it could be possible that it has no need for any rubber flex lines as the electric compressor unit is mounted to the chassis and could use hard lines all round (though will confirm that)
As long as the AC is performing well no need to replace gas.
An off-topic comment: the weak links in traditional automotive A/C systems are the hoses and the face seal.
Barrier hoses were introduced with R134a, a quarter century ago. They leak much less (1% or less) than traditional rubber-only hoses. While the diffusion isn't negligible as it is with steel or copper lines, it is rarely an issue.
The face seal is the rotating shaft seal, required because the input power comes from an external belt drive. It's typically two disks with a carbon-carbon, carbon-steel or carbon-ceramic interface. The initial pressure provided by a spring which is supplemented by the internal gas pressure. Each disk is sealed with an o-ring, one against the shaft and the other against the case. Even with wide disks, there is some migration of refrigerant past this seal.
Getting rid of the external drive allows eliminating the shaft seal. It also might allow getting rid of all flexible lines, although sometimes it's easier to design or assemble with them.