Before doing surgery to the refrigerant system pull inside output vents and check for sealing of cold air from going inside roof instead of inside coach.Buy a rool of aluminum Duct Tape and fix if there are gaps.
Then on top pull cover off ac and check for cotton wood tree seeds and any other blocking and clean and the fan too.
Have someone turn it on from inside while observing and listening on top.
Low refrigerant will cause the evaporator to freeze up and water should drip from ducts inside as well as drain if that is the case after turning off and given time for ice to melt.
The front ac always catches whatever is in the air going down the road first.