I'm wondering how PepBoys determined that the system is fully charged. It seems that the most likely scenario is that the refrigerent level is low, resulting in poor cooling.

Has the system ever been converted from R12 to R134a? If not, then I'd suspect that the refrigerant level is too low. Can you see the center of the compressor turning when the air is on? That is, the area on the front of the compressor inside the pully should turn. If it's not turning, then the compressor is not functioning. It could be because the refrigerant is too low and the pressure cutout switch is preventing the compressor clutch from engaging. If the pressure is OK, there may be an electrical problem with the compressor clutch.

I think the first thing to do is get another opinion. I can't imagine too many circumstances where the charge would be OK and the compressor would be fully functional but there would be no cooling.

Let us know if it's R12 or R134a, and how they ensured that the system is fully charged. That may provide a starting point for diagnosis before you spring for a mechanic's bill.

Robert