I have a 2003 Supercrew 5.4 Lariat with the electronic climate control. Problem with the air conditioning is that most of the time the cold air comes out the defrost vents. (Air is cold. It’s just coming from the wrong vents.)

What I have noticed is that when I put the engine under a load (like accelerating or going uphill) and then release the load (take my foot off the gas), then moments after I release the load the problem will correct itself and the cold air will come from the dash vents like it is supposed to. Everything will be OK for a few minutes, but eventually it switches again and the air will go back to the defrost vents.

I can repeat this anytime I want while driving down the road. I hit the accelerator and then let off, as I let off the gas the air comes back to the dash and then it eventually goes back up to the defrost vents again.

One time several years ago I a similar problem, except at that time the air was always coming from the defrost vents. I did some research and found a broken vacuum line between the vacuum reservoir (on the back of the battery box) and the firewall. I fixed that leak and it solved the problem. This time I replaced that entire vacuum line from the reservoir to a check valve in that line just before the firewall, including replacing that check valve. This time it did not solve the problem.

If anybody has any advice about how to diagnose or fix, I would much appreciate it. Dealer will charge me a boatload to fix what I’m afraid is a simple vacuum leak. I’m not above spending a little money and time to replace a bunch of vacuum lines on the hope that it will fix a problem (like I did with the one I just described) if that’s what it sounds like to somebody, but I really don’t know where to start to begin to diagnose it.

Any help is much appreciated. Thanks a million.

 

I had this problem, the air would always blow to the defrost replaced al the o rings in the control unit I found a lot of help from others google it is how I found it. Best I can do for ya