If they are set up anything like the Neons then they are cable operated doors. If so then the cable could be off on the back of the control head or at the heater box. The doors inside the box are probably plastic. When it's on the defrost mode it will only be on vent mode. That's the way my Neon works. Once you switch over from defrost to any of the other fuctions then you can rotate the knob from vent to recirc.