Can the roof AC be recharged ?

Yes, they can. BUT, to NEED Freon, there has to be a leak in the metal sealed system. There are no rubber or any type seals that can leak like a home or Auto type system. So, if you need Freon, then you must FIND the leak, fix the leak, then install Schrader valves and evacuate and charge. THAT process takes more time and money than just replacing the upper unit. RV units have had this design for over 50 years. Doug