First thing that comes to mind is the blend door actuators. I know in my 97 PA I had mixed air not just coming from the "mid" dash vents, so there was a loss of air pressure and not that cold either. Long story short, I pretty much had to replace 3 door actuators, to get it working right.
When u turn on the auto setting and lowest temp the air should be on the middle vents only, is that where all your air is coming from for starters?. When on defrost, I also had mixed air on floor, before new actuators were installed.
Chances are the actuator may not be closing outside air so it is not getting as cold as it should. #604111 They look like this: http://www.rockauto.com/catalog/x,ca...parttype,10721
They are located behind glove box near firewall inside.