A/C Selector???

what could be wrong? my a/c selector is stuck on defrost. it wont go back to the vents when i move the selector. could it be a bad selector, vacuum problem, or my blower motor. my blower motor is acting up too. i only have one speed and that is like the lowest speed ever. any help is appreciated. thanks

The defroster is the default position. It sounds like you have a vacuum problem. Check the vacuum connections on the engine side of the fire wall. Depending on the year of truck, you should find a three way connection which is a check valve tow connections are small and a large one from the vacuum tree. One of the small ones goes to the vacuum reservoir and the other goes through the fire wall to the selector control. Either you have a broken line or component. On later years the check valve is built into the connection to the vacuum reservoirs.

I had a similar problem. Mine was not switching to vent when I turned it on. It was indeed a vacuum leak. On the passenger side, right at the air box (where the blower fan is) there is a vacuum line that controls an arm to an internal door, which directs the airflow. The arm is easy to see, right in the corner of the engine well. You can manually push it, and feel how it operates. If you've lost vacuum, it won't work at all. Look at a bundle of wires coming through the firewall just to the right of the air box (when standing in front of the truck). One of those is a vacuum line that goes directly to the control inside the cabin. Mine was broken right there. It's small (about 1/8" or so) and black (I think, or if not, it's red), and looks almost like an electrical wire...but it's not. I took a piece of small diameter rubber tubing and spliced the vacuum line back together. Works fine. I think it's probably more likely to break inside the engine well, as it's partially exposed, than inside under the dash...unless you've been working under the dash.

Snowman74 >-