Just had the truck in the dealership for a bad blend door/ heater core case. Heat would only blow out warm on the passenger side, blows cold on drivers side. Dealership replaced the case, heat works normal on both sides now. It was a little warm out yesterday so i turned on the A/C, frosty cold on passenger side, warm on drivers side, temperature does change when i select different temperatures (dual zone.) Any ideas guys?

 

Take it back to the dealer.