I have a 2003 dodge grand caravan sport, 3.8l, v-6. I am having touble with the ac. Or it seems to be the switch/knob that adjusts the volume of air blown out the vents. It works sometimes and then not at all, more recently its not at all. I can put my hand up to the vent and still feel cold air coming through the vent but with out any force behind it or ability to turn the fan volume up. The knob has no resistance but does not feel as if the plastic knob itself is loose, it seems more complicated or involved than that. HELP PLEASE!