Not long ago I discovered that I had a dead battery. After recharging @ reprogramming my 98 SL500 everything seemed fine. Then when I killed the car I sat listening and hear a small, very quiet fan blowing up thru the Defrost. The only way I can keep it from draining my battery is if I remove the large green 15 fuse. I have to open the hood and plug it in to have AC or heat now... Can anyone tell me which part needs replaced?