The very famous and expensive BMW AC "wheel" found on the E23 and some E32 seven series and I believe five series as well does break down (stops working) almost on a yearly basis and has to be replaced. This unit controls the volume of air you get inside the cabin -- when it breaks -- no air whatsoever -- which is really a pisser for those of us who live in hot weather states !! This is, in my opinion the worst by far car part BMW ever made -- which is vexing because the cars from this era (1980's) are so well made and beautiful otherwise. Things could be worse however -- my friend owns the new 745 -- do not mention "idrive" around him or you will have a heart specialist capable of murder on your hands