I had a similar problem on 98 caravan. Try running it thru its diagnostic cycle. You do this by warming up the engine, with the engine running, turn the fan all the way on high, set the vent control to dashboard (not defrost and not floor), turn the temp selector all the way to hot. Then I held down the rear wiper and rear window washer buttons simultaneously until all buttons begain flashing. The system will then cycle through heat and A/C taking turns to blow out the floor, the panel and then the defrost vents. AFter it is finished, the lights should all go out.