sorry to say but symptoms suggest a leakage somewhere. if the evaporator has never been replaced, it is a likely culprit for a 2002. evaporators usually dont last that long. this will be a difficult diy as the dashboard needs to be removed. maybe worthwhile to go to a good ac shop that has the capability to check (e.g. dye injection) and identify the location of the leakage. if evaporator is the culprit, the last owner may have cheated you.