I had a similar issue on an 04 I had a couple years back. I read all about the air doors and didn't want to really mess with that process. I ended up removing the blower motor from under the dash and reached up inside with my hands and found the air doors broken and just flapping around in there. I pulled them both out through the opening where the blower motor was removed and then put the blower motor back in and I had heat in all vents including the defroster which I did not have before.
weird but it worked so not sure what the purpose for those doors are
I'm betting the AC leaves a lot to be desired.
The purpose of all those doors is to direct the air flow to all the available options (defrost, vents, heat, AC ducts, cool/hot and all the combinations of each) some people think they need.
My hot rods have a choice of defrost with heat, or off. I can regulate the amount of hot coolant flowing through the heater core, and I can control how fast the blower motor runs, or I can shut the whole thing off and open the outside vents. Gene
