Right from new the air-conditioning on my 2006 PA Mitsubishi Challenger has performed very poorly. The dealer tells me it is operating as it should and an independent specialist tells me the same, but it's not as good as the system in the NJ Pajero I owned before the PA. Given that the Pajero and the Challenger basically share the same V6 engine, would it be possible to upgrade my system using Pajero Components.
It's possible that you could change the system, but I would consult an air-conditioning specialist to get a clearer picture of the differences between the two systems, particularly with components like the compressor, drier, heat exchanger etc.