I have similar problems with my W202 that already ran on R134 when it rolled off the factory.

I can get almost no cooling if the car is at rest.... and only acceptable A/C when the car is on the freeway.... street is similar.

When you stop the A/C is pretty much non-existent.....and if you switch on AC (leave ACC to auto and set a lower-than-ambient temp) and park your car for a bit the water temp goes up to 100C....

before the R134 recharge it would not do that.... but I was confirmed by other members that this was normal. I haven't driven the car in the really hot weather yet (never above 25C) so I don't know if the hot weather will make the A/C work better or worse.

But if your car isn't moving yeah the A/C is definitely not too happy about it.