A/C question, no middle vent air???

I know this probably wont help much but then again it may. Here is the only diagram I have that deals with the AC system. I beleive that which vent the ac blows from is determined by some sort of vaccum system and that most of it is accessable without tearing the dash all the way out. Maybe removing the ac controls or under the dash. I know its not much but maybe a start for you.

http://www.veryuseful.com/mustang/tech/engine/images/mustang88AC_Controls.gif

It could be the vacuum line.
Get your head into the passenger foot well and look up under the dash next to the center console and look for a vacuum control cylinder, (brass in color). A yellow vacuum line should be connected to the side of it via a nipple. If it is disconnected, you will have the problem you described.

I have this exact same problem... sorry that doesn't help u much.

the vacum control!!

its not on the passenger side its on drivers side towards center of car behind the door/igniton dinger and to relays are in that location its behind their when u flip your switch control it should b movin one way or the other if its not check the clear vinyl line that is the vacum line remove it and hold your thumb over opening in the line u should feel suction when u move control one way and release when moved to another positon if you feel this transfer line is ok then it will probably be a bad vacuum diapgram. if you donot feel a trans fer of vacuum then it could be in your switch control!! i have my dash apart now if you need photos let me know i will take them of everything you should look for!!

check the little beer keg with thw yellow line and if its not that check the vacuum coupling under the glove box i had the same problem and it was one of the lines by the glove box. good luck phil