Im having an odd problem with my heater in my 83 300sd. Some times you hit any button and the heater kicks right on other times the blower will turn on but no hot air. Sometimes it just wont turn on all togehther. When it dosent work none of the buttons work and when it does they all work. I dont know where to start with this problem any help.

I had a similar problem with mine. It took me forever to find this. It turned out to be the ignition, after it return to the on position from the start position, it wouldn't go all the way back. There is a notch on the key cover that lines up with the bezel of the ignition see if they are aligned.