I am having an almost identical problem as mb96 on my 91 300E. The defrost was working fine a few days ago. Yesterday, as I was driving and had the fan on, heat started coming out of ALL the vents. I adjusted the temp wheel all the way down to see if start blowing cold air but it did not improve. It got so hot I had to pull over the side and noticed the dashboard was hot and the little light in the recirc button was blinking. I shut the engine off and when I restarted the engine, the fan does not run anymore but I can still feel the heat from around the dashboard. Any idea as to the cause of this problem? Also, psfred mentioned about fuses. Can anyone tell me the location of the blower fuses. Thanks.