My F-150 recently decided on it's own to blow my A/C, heat, or defrost out of the windshield and floor vents only. No matter what I selct on the dial, I only get floor and windshield.

Is a vacuum line defective or are these electrically controlled? I'd like to fix the problem before summer shows up.

Thanks,
GLW

If you have the climate control ac , some have a module that controls the airflow, with a small processor. Others are a combination of mechanical/vacum controls. Check under the hood, on the passenger side, there should be a plastic vacum line going through the firewall, or into the evaporater /heater core housing. These are bad about cracking and breaking. Here where we live, we have a problem with rats and mice. They love to chew on those lines for some reason, and sometimes in spots that are hard to see. This line goes to the control on the dash, and is usually where the problem is. Some have a cable that controls the heat selector, not sure which setup you have. Good luck.
Later
Ed
.

Just to let you know. I finally had time to work on the truck today and you're brilliant. It took about five minutes to solve th problem after noticing the cracked hose near the firewall.

Thanks again,
GLW