Doing some minor tinkering. We filled the A/C system with R134a over the weekend because the rear air barely blows cold on these things. It has 50 feet of aluminum lines and a separate rear evaporator and expansion valve in the right rear corner, quarter panel. It takes 6 cans and the high side system spec is 330 psi according to the factory manual. Filled it up to spec and still not very cool at the outlets.
One of the reasons for the underperforming rear A/C is that it also has a heater core and 50 feet of aluminum line running to the same ac/heater box in the rear corner. The only thing separating them is a flapper valve to direct the air flow from the bower motor. But the heater core still is in the same box and all that ambient heat just does a "Reverse Uno" card move on the cold evaporator.
So I decided to add a heater core bypass valve in the engine compartment. They make these for this exact reason: to bypass the hot water going to the heater core in the summer and return it to the radiator instead. In the winter you just turn the 90-degree valve and you are back to normal. Already seeing an improvement in coldfulness coming from the upper roof air outlets. Don't know why I didn't do this years ago?
Here's the valve:
https://www.amazon.com/dp/B0CLTZD1TW...sin_title&th=1