a/c blows cool air in the front but blows warm air in the rear passenger on dodge durango?

The flapper is located inside of the rear interior panel that corresponds to the hoses entering the truck from underneath. The blower unit, a/c condenser, heater core, temperature selector flap/actuator and vent/floor selector flap/actuator are all behind that panel connected to one large unit.

It takes a bit a disassembly of interior panels to get in there to do the work, but it's nothing terribly tricky if you're used to working on car interiors and are handy about it. Just be warned, there are a ton of screws if you have to go in there.

Definitely check the core for hot send and return hoses first. It could save you a lot of time and hassle. If those are hot, then you'll have to check out the actuator door. I kind of had to carefully pry the unit apart to inspect it, remove the broken flapper/pieces, and install the replacement.

I got a replacement actuator and flapper door for about 20 bucks at the junk yard and it took a few hours to get in there and finagle it into place and reassemble everything. I tried to avoid taking the whole thing out and succeeded.

If the actuator flapper door failed, I'd have to suspect that either the collar that connects it to the servo motor broke and/or the door's mount broke. The servo motors don't seem to fail. Unfortunately, the actuator servo that drives the flapper door is very powerful and can easily overpower the little plastic tab-stops on the assembly. Once those fail, the door travels a bit further than it should, and then bottoms/tops out inside of the HVAC unit. At that point, the actuator keeps going and then snaps off the flapper's mount.

Once it is broken, the flapper door just lays on top of the heater core, which allows the air to just bypass the heater core altogether, much in the same way it would had it been fully functional and you selected cool air (or AC).

Since the part and servo I got from the junk yard wasn't broken, I figured it would be worth using the servo motor that came with it instead of keeping the one that broke the other door in the first place. It was a slightly different make than the one I had in my truck, but it was still a plug & play operation.

I really wouldn't let the dealership do this repair, as it is a little on the labor-intense side for disassembly and reassembly. The part is cheap and the actual repair is quick though. On top of that, the dealership will want you to buy an entire new side to the HVAC unit, which is big $$$ and much more than you need to buy. Who wants to buy the entire unit when all they need is one or two small parts? It saved me a ton of money to do it myself (as the rear heat and a/c is really not a crucial system anyway), and it shuts up winy passengers in the winter.

These heater lines-------- run under the truck and enter the underneath side of the rear passenger side corner. There are 2 hoses (heater) and 2 hard lines (air conditioning) under there.

Read this session of one of the user facing this same problem:-----

I have an 01 Durango SLT, 4.7L and my Rear Defroster button is Flashing and the AC button next to it is inoperative as well. Also cold air blows out in the rear(Front heat works fine). Took it to the dealer where they scanned the HVAC module with a DRBIII scanner and a "Rear Blend Doors Broken" code popped up.

Took the car back and I disasembled the passenger side interior trim myself exposing the whole Heater/AC Assembly. I found that the first door flap and white plastic nob that controls the door flap which circulates between hot air and cold air is broken.Replacing the broken parts solved my problem.-------
Here's what I found out and what I did to fix my rear HVAC. It turns out that Dodge no longer offers a replacement temperature blend door, at least by itself. It seems they realized a design problem, and so they have redesigned the half of the HVAC housing that holds the actuators and doors. So to get a new flapper/door, you've got to buy the whole half of the housing. Which also means you probably have to remove the whole unit from the vehicle to do this work, too (mine was still in the rig). Cost? $189.00. So I decided to attempt to repair the broken piece myself.

The good news is that the actuator knob, actually called a coupler, is available, and so for $10.10 I had a new coupler. This saved me the trouble of trying to repair the broken limit tab from the original coupler. The parts look like this:

The flapper door and it's broken piece are obvious. The new coupler is the black piece. The broken limit tab from the original coupler is the small white piece. Note how they've redesigned the coupler tab as a beefier lug that runs the length of the coupler hub.

I epoxied the door pieces back together, and reinforced the joint with some small gauge wire. Everything went back together fairly easily. Here's the HVAC housing before replacing pieces:

The white "knob" in the middle near the heater core plumbing is the original actuator coupler. I drilled this out and replaced it with the new, black coupler.

After getting it all back together I ran it through the different operating ranges. Thankfully everything worked. The system appears to self-calibrate. The temperature actuator cycled itself from one extreme to the other, and then the unit responded properly to changes of the temperature setting. One problem -- I noticed that when the coupler was rotated to full clockwise, it appeared that a fine crack was just starting to open between the HVAC housing and the limit stop built in to the housing. So I made an aluminum support for this limit stop, not wanting to have to tear into this if the limit stop broke later.

Hope this is useful for the reader.---------------

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