When the air flow comes out of the defrost only. 99% of the time you have a loss of vacuum somewhere. Normally not the control head and after 15 years of working on these A/C problems, I can only remember replacing one control head and believe it or not the new one was worse then the old one. Went to a junkyard and got a used one from another vehicle and it was fine. If the leak is very small, you might experiment by turning your heat on to the floor or dash and in park rev your engine up and see if the vents try to change to the correct settings. this is not full proof but it is a cheap test. If theairattempts toblow out the correct vent then you have a vacuum leak. If not the problem could still be vacuum, just a larger leak. Check hose going to the vacuum reserve (the coffee can shaped thing) normally locatedunder the hood attached to thefender wells, some are a round ball about the size of a large grapefruit. Only one small hose going to it. If you can find the main vacuum line going to the fire wall you might try disconnecting it and see if you have vacuum there. Good luck, vacuum problems are exactly that PROBLEMS...

 

I haven't had a chance to really look into all of your suggestions, but I did try changing which vent the heat blows out of. Mine blows out the dash only. When I changed the direction of the heat to the floor, the system acted as if it was going to switch for about 5 or so seconds and then started blowing out of the dash again. I haven't checked the vacuum reserve yet. But I'm guessing that you are right, that it is a vacuum leak. So, how do I explain it to the dealer well enough to get them to believe me? They can't seem to get past using the computer to do the diagnostic on it. The computer keeps telling them that it's the control head.

 

I thought it was just me but my floor vents don't really do too much either, defrost fine.