a/c not cooling correctly
 

I have a 1990 911 C2 that has had an ongoing cooling problem. I have replaced all filters, evaporator, and drier. There were some leaks on several hoses and fittings allowing freon to escape, and all these issues have been fixed. The pressures are all holding and at the correct levels. My mechanic seams to think that the air flow is not directed over the evaporiator coil, or there may be some hot engine compartment air flowing under the dash and conflicting with the a/c effectiveness. Anyone ever had this issue, or have any other ideas for this issue. The car is black and I live in South Texas where we use a/c about 9 months a year.