Not knocking the Dealers, but they are always suspect due to they want to do everything from A to Z and not what really just needs it. I had a similar problem with mine in the rear and in the front too. Hard to type, but is it ever intermittent? Where like you get non-stop cold air, but if you shut down the truck you get heat? Then it is OK, but then loses it and you are kinda going back and forth like that?
Their is a part behind the right side under the huge plastic on the right side cargo window called a blend actuator. This is what tells it to blow what temperature of air. Meaning it controls if it is going to blow hot air, warm air, or the AC? where it is bad and has no clue what temperature air what to blow by what you set it at. Just like if you put on the AC in the summer and got hot air. Get the picture? This part controls that. Super easy to change and I could walk you through it and takes probably 20 minutes if that.
With the front ones I have been through them as their are I guess 3 of them in the front and the 1 in the rear. They all look identical, so just don't get one they all are different.
Mine started with the front and it was like possessed where it started in the summer with my front one. I would have cool air blowing on me and passenger would say they have heat, or just warm air. Then I would shut it down and start it back up. Then it could be me with warm or hot air and passenger with cool air. No rhyme or reason with what it was doing obviously.
Fronts are a no brainer and all simple to change but 1 and they start out going bad by you hearing a clicking noise. Then they get erratic, then they break.
If you could give more details on the 30 to 45 minutes to get heat if that is all the time? Can you shut it down when it is blowing cool air and then you get heat? Did it ever do anything like that before? I know rough with you driving just like me with driving and not always having a passenger as how mine was discovered due to I did not know. If it is that part the back is super easy to change, but put out some more details or message me I have replaced the front 2 times now and the rear once.
To me it sounds like it could be the blend actuator in the rear went bad, but message me some more details or put it on here due to that is what controls the temperature you are going to get.
