My front and rear ac worked together as a system. The front wouldn't work unless the rear was on. They shared a compressor but I think they have separate evaps. I had the carrier system in my bus. It is now removed. No more AC.
My 2000 E-450 Aerotech had a roof mounted rear condenser but no engine mounted condenser at all. I removed the rear AC to make way for a shower so I had to put in a new condenser in the engine compartment. Had to buy a few new hoses to hook it up but at least they're easily available.
that rear ac blew so cold i decided to keep it. i was able to drop it to the floor fully connected, with only minor things to weld back together. Im going to mount it under one of the bunks so i won't have to run a generator while traveling.