Another possibility,,,, particularly on these sometimes strange MB's is a vacuum line misplaced... some of these cars use the heater to modify the passenger/driver temps... and so the heater flap could be engaged where hot air is blowing... as compared to ambient temp air blowing... don't know if he was making that distinction in his description or not...



My 300-D had a similar problem. The air never really got cold enough, yet when my mechanic checked it the freon level was fine. He showed me an inexpensive trick to keep the heat from combining with the cold: get a little vise-grip wrench and crimp the elbow shaped hose near the firewall of the engine compartment. Be sure to wrap the hose with some electrical tape first. This will prevent any heat from entering the cabin, but you will no longer have any control over the temperature of the AC (it will always blow at the coldest temp). That method worked for me instead of a costly repair. To regulate the temperature I simply turn off the AC for a little while. Near winter, I'll remove the clamp and have heat as usual.
Hope this method isn't too unconventional and it helps. (BTW, my mechanic is pretty well respected in the DC area.)