A/C has almost no power

What is your question?

I recently had my A/C rechanged since it wasn't cold anymore. That fixed the cold problem, but now the A/C doesn't blow very hard. I have two questions: 1) How involved a problem is this; i.e., can a mechanic fix this on the side, or do I have to bring it into the shop? 2) Which part is it, and roughly how much should this cost? Thank so much, Jeff