Only three times in four months has this symptom occurred, but I'm wondering how serious it is.......The climate control in my 90 500SL will select full fan and full heat and won't relent, almost regardless of the temperature setting. I normally leave things in AUTOMATIC mode at about 70 degrees. I have to open the center "Cold" vent just to make things bearable. This has occurred in outside temperatures ranging from 25-40 degrees. Things seem to get back to normal operating mode the next time I use the car, which is often the next day.....Any ideas of the extent and expense of this problem???