I just went through this. The problem is the recirc door and housing. I got the part for $16.00 from the stealership. They wanted $755.00 to put it on. I freaked and said no and took it home. Now I know why they charge that much. LOL! I had to remove the entire dashboard to get to the passenger side firewall to replace it. I must have removed like 200 screws and bolts. It was a PITA!! I probably will never do it again for myself or anyone else. My temporary fix was to remove the blower fan and reach up and yank out the recirc door. By doing this,,,at least I had all my zones back, I just didn't have recirc anymore. hope this helps some.
Fletch
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2005 4x4 QC 24V, Predator/Power Puck, 315's Mickey Thompson MTZ, Leveling Kit, Dual Steering Stabilizer, Stainless Gage Insert, muffler MIA, Cobra CB, Limo Tint, Sirius, Dual DVD Players, LED Tails, Tailgate Lock and Whelen strobes.