If the back is blowing cold and the front blowing hot the most likely culprit is the temperature blend door or servo motor, could be jammed, broken or the motor has just quit, most repairs on this means that the entire dash has too be removed, so I would recommend that you take it to a shop you trust and have it checked.
The other culprit could be the ac expansion valve not working correctly its under the hood on the back firewall passenger side, it looks like a block of aluminum.
Search Dodge Durango Questions
Dodge Durango Experts
Related Models For Sale
Used Cars For Sale