If you hold your finger in front of the brush with the trigger down, do you at least feel air coming out? If so, and assuming that it "Feels About Right" then the problem is in the paint system. If not it is in the air portion somewhere.
I'm not a Paasche person, I use Badgers, but I found a parts breakdown of the "H" model on Paasche's site and it had this information in it:
HOW TO OPEN CLOGGED FLUID PASSAGES
1. Agitate color in Bottle Assembly by placing finger momentarily over HC- Aircap while air is passing through the Airbrush. This will blow color back into bottle thus opening clogged fluid passages. Do not do this with a cup as color may blow out of cup.
2. Should H-1, 3 or 5 Color Adjusting Part Assembly become clogged, loosen H-153 Set Screw, unscrew HT-1, 3 or 5 Tip from HN- or HNS- Needle, gently pull back through ball-shaped support and remove Tip.
3. Clean Parts carefully, using nothing harder than a wooden toothpick.
4. To reassemble, reverse this procedure, making sure the shoulder of the Needle seats up against ball-shaped support.
5. If the needle and tip are completely clogged, soak in a closed bottle of proper solvent until clean.