I am trying to fix a '93 Ford Areostar van and service manuals are no help with the problem. The AC and heat both work and the fan speed seems to adjust fine but all air comes through the dash defrost vents making the AC useless. This is the longer version van (4.0L) with rear fan controls. The dash is the electronic style, but the Heat/AC switch is standard turn knobs. I have been told it might be a blendor motor or vac. switch but no one, even service techs, seems real sure of this or even where these parts are located.

Paul Creef, July 2005

Usually on gm cars and vans when it only blows out of defrost you have lost vacum to the ac and heater control head in the dash. If you look for vacum line going into dash under the hood you can proably find it .......pinched line or correded , split line.
Or pull ac control head and check for vacum @ the 9 port vavle

bg, October 2005