Hello- I just wanted you to know that my daughters' 190d has exactly the same problem.
Was recharged last week, they said that they couldn't find any leaks. (previous owner had stated there were leaks) 10 minutes after leaving the shop in slow city traffic it started to cool down a tiny bit. On the freeway it actually got cool enough to i could take it off 'max' setting. Alas, when back in traffic, we both had beads of sweat on our foreheads. Perhaps because we spend $200 for a five degree temperature drop?
The only thing we've been able to do is keep it on the max setting and keep the vents at 1/2 way open...this seems to make the air cooler by limiting the flow. Sad, i know, but I wonder if you might be doing the same thing...

Frank


1986 Mercedes 190D
1996 Saab 900
2004 VW Jetta GLI