Ford Repair: a/c, vent air, control switch

Question
85,5.0 4v GT  a/c runs in all modes exept vent .air comes in when off.temp ctrl works.is mabey bad selecter switch ?

Answer
Joe, a schematic would be very helpful for your concerns.. the compressor is designed to run if the control is set to 'Max', 'Norm', 'Floor-Def', or 'Def' to cool and dehumidify the air.  It shouldn't run in 'vent' or 'heat' positions.  If it does, I would suspect the control switch is burnt and shorting a couple of the pins together.
The blower motor should not run in the 'off' position either, so that again sounds like the control switch is burnt.
Hope this helps..
Clay