I have a 2006 Ram with the 5.7 liter Hemi. Recently the A/C ducts and vents stopped working correctly and now pretty much don't work at all. What I mean is that the fan works and the temp works but I can't get the air to go where I want it by selecting the windshield defrost or directing it to my feet or whatever. It's like the valves or gates, whatever you want to call them, don't move when I turn the selector ****. I should be able to hear and feel the valves changing positions when I go from defrost to another position but now nothing happens about 95% of the time. Once in a while I will hear and feel it change something but usualy not what I wanted to change. And even if I get it to change to a certain position I don't get the air flow I should. When it worked, if I put the fan on high it would pretty much blast the air out at you. Now it feels like it's on low or maybe medium low. I usualy just get a tiny bit of air coming from the defrost, the main air vents and the foot vent, all at the same time. Very weird. I looked up under the dash while changing the setting but saw nothing moving at all...not that you can see a whole lot under there. Do these things still work on vacuum like they did back in the day or are they all electric? I have had this truck for 3 years, almost 50K miles and this is pretty much the only problem I have ever had with it.

 

I have read about this in other threads, i think it is call the blend door or something like that. From what I have read it is a pain in the *** to replace yourself and pretty spendy to have the dealership to do it since the dash has to come off. If you search the forum you will find it.

 

This might help
https://dodgeforum.com/forum/3rd-gen...-with-air.html

https://dodgeforum.com/forum/3rd-gen...ator-door.html

 

If you still have warranty, take it in. Depending on which door it is, it can be an expensive fix.

Here's an aftermarket do-it-yourself fix with metal doors so it does't happen again. The video gives you an idea of what going on there in the HVAC. It shows you how to fix without pullling the whole HVAC box out. Not for everyone though as you do a little hack and slash to the HVAC box.
http://www.heatertreater.net/Dodge%20Ram%20Video.html

 

I just resolved a similar problem, even with a warranty the dealer was going to charge me $50 just to determine the cause. I investigated it myself and discovered that the door that changes the air flow from outside (fresh) to inside (recirculate) had broken off it's mounts and was laying across the top of the blower fan, not allowing air flow to the fan itself. It was really easy to remedy, 3 or 4 screws let the fan drop out without disassembling any of the dash. Once the blower was out, all I had to do is reach in and pull out the "flap", it is big, but will come out through the hole. It now blows like it used to. I do plan on taking in the door to the dealer and asking if "this piece that seems to happen alot" is under warranty, but for now it works just fine without it, Really who cares where the blower inlet air comes from.

 

It's normal to charge diag time. but when it turns out to be warr the diag time go's away if your dealer charge you diag after they find out it's warr call chrysler. the problem is that untill they know what's wrong they dont know if it's coverd. You may think everything is coverd but thats not always the case. I had a cust with an elec problem. Lights not working stuff like that . when I pulled the controller out it was full of water. he had a plastic water bottle he kept on its side laying on the dash and the lid was loose . Not coverd even though it was 2 years okd and had 15k miles on it. so ask the service writer if it is warr you will not be charged for diag?

 

I had a broken Re-circ door replaced on my '06 Ram under warranty also. Seems pretty common.