I have a 2013 Ram 2500 Cummins. It is a tradesman model so it doesn’t have seperate climate controls for driver and passenger. At highway speed the AC doesn’t blow cold on the driver side. Driving around town or idling the cab gets nice and chilly but as soon as I hit the highway the drivers side vents warm up.

 

Hi, I had this problem on my Wrangler JK. It was the interior radiator that was blocked. We had to dismantle the entire dashboard to change the radiator. I don't know if there is the same problem at Dodge, but it was an original problem. There was sand inside the cooling circuit which blocked the heating radiator. If it helps, good luck.