So the rear heat/ac only blows cold as the common problem.
I pulled the back panels off and went to looking for the common issues. Blend door is intact and rotates. Servo rotates. Heater core lines are hot. But the air is still cold only ever so slightly better than cold.
While trying to diagnose the problem I was feeling the lines while running the Durango and noticed the heater core is cold even though both lines are hot. So I undid the screw holding it in place and pulled it out a little and the fins on the core are cold. I am no expert but shouldn't the main part of the core be hot? Correct me if I am wrong.
Just want to diagnose this and buy the proper stuff. Only place I can find a heater core for the rear aotm is on rockauto.

 

Don't quote me on this but I *think* there is actually a pump that circulates the water back there. It's on the passenger side firewall and hooks to one of the heater core lines. If teh pump isnt working then it would make sense that the core is cold. Core could also be blocked.

Bob

 

Did you actually open the box and check the doors? If the in and out lines are hot its probably not a core issue!