Patient is a 2004 2500 TD 6Spd 4x4 QC 8ft bed (if that matters).

My tuck has dial ***** for fan speed and vent configuration. Few years ago, I noticed that sometimes when I switched to blow air on the windshield, air would not go there. I used to play with the dial **** until it eventually switched. Guess what? That work-around doesnt work anymore. The air can still be sent to legs or front vents, but will no longer go to windshield, which is highly annoying when it is fogged up. I have not looked at the problem at all yet and was wondering if this is at all a common problem, whether there is a common culprit and in what order should I start to troubleshoot this?

Thanks in advance!

 

You have one or more broken mode doors. Google Heater Treater, and they will give you the info on how to diagnose.

 

For the record, I ordered the 4-door heater treater kit. Their "certified local installers" did not return calls - I tried 3 different outfits. The fourth told me that they do not install customer-supplied parts...

Anyway, ripped the dash apart to get at my air boxes. The job is a sizeable pain in the *** and the latter steps called for you to cut/dremmel the actual air box! These parts are not direct fit - they effectively have you slice open the air box in different places to get at the various doors, then give you some goo to glue the holes back together. The instructions weren't great and the videos left something to be desired. Honestly, didn't sound like something that I wanted to do.

I did however test the function of my doors, as they instruct in their videos and all of my doors were in perfect working order. I ended up mailing my kit back to them and eating the 15% restock and shipping fees. In the end, I am 99% sure that the selector switch on my heat control panel is dirty. I sprayed the crap out of it with electric contact cleaner and it works much better now. Will need to replace it at some point.