Sounds pretty cool, but just preprepared put more into the AC. If an air-conditioner needs a freon charge that's because there is a leak somewhere. A healthy AC system will never leak. My guess is AC work on a Mercedes would be out of sight.

I would take it somewhere and get a diagnosis of the AC, before you commit to it. Might be something as simple as a hose, but I doubt it. Usually the compressor, that's the moving part.