Before you do anything use the OBD to try and pin point the problem. Turn the ignition to run, press and hold the "off" and "warmer" buttons on the Climate Controll Center. The fuel gauge should flash 888 then start listing off numbers (E.E.45, F.12, ect.). Write them down and refer to a Shop manual for their meaning.
Otherwise this is what I did to fix the same problem. Remove the glove box and find the mixer door controll unit (black box with 5 color coded lines runnig into the bottom of it). Change the temperature on the climate controll centrer. The metal rod connected to the air box should gradually move as the temp is adjusted. If it doesn't, pull the multi colored vacuum harness from the mixer door controll unit. Place your finger over it (engine running) there should be signifficant suction. If not, a common place for a break is on the filter box under the hood (located in between the Maxi fuse center and the brake master cylinder on the firewall). Two lines connect to the bottom of the box make shure both are still connected. If you had vacuum suction the whole time but the rod to the air door wouldn't move replace the mixer door controll unit. If you still have promlems trace every vacuum line for leaks or replace the PROM chip in the BCM computer. Hope some of this helps.
