[MidnightBlues]

On my truck there's a vacuum thingy on the firewall on the righthand side wich moves the flap for the defrost/heater outlets.It's near the heater box.It is controlled by vacuum,and moves when I go from airco to heater.When in airco position,it shuts the heater outlets.Maybe there's something wrong with yours,at least there was with mine.I removed the vacuumhose.I don't use the airco.
Hope this helps.