I have a 2003 dodge durango and the rear seat heating vents blow out cool air when on heat, but the front row and third row blow heat??

SOURCE: no heat or a/c from second row vents

I have the same problem with my 2002 Durango. After accessing the rear HVAC unit you will find that there is a rear electronic actuator that operates a plastic door inside the duct system. The door switches the rear system between heat and cold. I had two broken items, the white actuator connector has a tab that broke off and the door inside the duct has broken where this connector fits inside. I am still trying to find the parts on line. I do not know what the part numbers are for these two items. Hope that helps, it seems to be a typical problem with the older durango's.

SOURCE: 2003 Dodge Durango front row fans not blowing.

2003 durango, front fan switch only runs on high, rear fan switch runs fine in all settings

SOURCE: rear a/c heat vent do not work

Sounds like the flapper valve for the rear heater/AC core is not doing its job to send the air through the AC core when called for.

Another clue of this is the fact that the air is coming out on the lower vents when it should be up high fro AC.

Have someone listen back by the fan inlet in the back usually on the right while you switch between AC and heat to see if they hear any noise or change in air flow.

Worst case is that the interior panel there has to be removed to service the assembly behind it.