I've got a 2000 Grand Caravan that just developed a weird problem. When the Heater Temp slide is set to the Hot end, heat only comes out of the Defroster duct by the windshield regardless of the setting of the vent control. Set it on floor,vent,etc it still only comes out of the defroster duct and makes no sounds as if it is even trying to change positions, BUT if I push the A/C button(and move slide to cold) then I can change the location the air comes out and I hear a loud clicking or snapping sound from the defroster vent area when going to and from the defrost position on the ****. Any ideas?

 

Could be a mode door or actuator.You may want to have the van check for codes in the HVAC system.