These RV roof air conditioners are unfortunately considered by the industry as being disposable rather than serviceable. They are not like automotive or building central air conditioners that have valves for adding refrigerant. Many other consumer products such as window air conditioners, refrigerators, freezers, etc. are the same. The refrigerant is added during the assembly process, and the copper tubing is crimped and brazed shut.
This Spring I also had to replace my front roof air conditioner. I took off the shroud cover and could see where the refrigerant had leaked at a brazed "T" connector on the copper tubing. My kid and I installed a new roof upper unit for $430. It was actually pretty straightforward and took less than an hour. The new one worked with the existing relay board box and interior ceiling vent.
2010 Georgetown 373
2013 Jeep Wrangler