1995 F150 A/C Problem
 

I was driving to work the other day with the air conditioner on and the weirdest thing happened. The air stopped blowing out of the dash vents and started blowing out through the defrost vents (WTF!). It did this for a couple minutes and then started blowing out where its supposed to and then started blowing through the defroster again. On the way home the air only came thru the defroster and has stayed that way since then. All thru this time I have not touched the controls. I was thinking its a vacuum leak but I inspected the lines under the hood and under the dash and didn't see any cracks or breaks. Maybe its the vent controls? Someone help me please.:-huh

Take a look at this thread. Especially Sporttruk post.

https://www.ford-trucks.com/forums/8...c-problem.html

Your truck most likely has have a vacuum leak. The first thing I would look at replacing is this little T shaped check valve located on the passenger side inner fender on the front of the heater/ac box by the engine. It the same valve that is pictured in that thread phoneman91 referred to in the post by sporttruck.