Does the display on the DATC say on for the short time after key off that the blower runs? If so, you probably need a new (used) DATC. Fortunately, these are easy to replace and not too hard to find. On the other hand, if the display turns off like it should and it's just that the blower continues running, then it's probably your blower speed controller. Unfortunately, to replace that you have to remove the dash or cut up the AC ducting. If it is the controller, I would replace the blower motor too, since it may have caused the controller to fail if it is drawing too much current for the amount of air flow.