Stuck on defrost?

Hello my name is Dave.

The most likely issue is in the vacuum system, without vacuum it defaults to defrost. I am attaching a diagram of the vacuum system for the HVAC for your truck. When you look at the diagram the part with the reservoir is the part that is under the hood. More than likely this is where you will find your problem.

When you find the reservoir, which is on the passenger's side of the engine bay, pull the hose off of it while the engine is running and check it for vacuum. If you have vacuum getting to the accumulator (reservoir) then it could be that the reservoir is leaking, a simple way to test this is to remove the hose going to it, plugging it and see if you get air from your vents when you switch it to them.

If you don't have vacuum to the reservoir trace the hose back to the check valve and from there back to the engine, looking for a cracked line causing a vacuum leak. If you find that your vents will switch while your engine is idling but not while the truck is in motion then you will need to replace the vacuum check valve.

If you could follow the steps I have outlined and let us know the results we will be glad to assist you further if necessary, either way would appreciate it if you could keep us up to date on your progress.

We look forward to hearing back from you and thank you for using 2CarPros!