1997 Plymouth Voyager flaching lights on air conditioning a

i have a 1997 plymouth voyager with 191000 miles on it,my problem is that the light on the air condition and recirulation button cone on and a chime chimes as long as the van runs.can you please tell me what is wrong i assume it is some kind of a warning but no one is able to tell me what it means. my manual sayes nothing about this.