I have searched this forum and not found a problem like mine. I hope someone can give me some help.

My car is a 1979 300sd.

In the summer the acc works perfectly.(auto-low and auto-high work ) Thanks to Larry Bible for talking me into keeping it R12 freon...Even in Augusta Ga, in the summer, it will keep me cool.

Now the problem, when I try to use my heater the auto-low and auto-high buttons will not work until I press the defrost or bi-level button. Once I press either of those buttons, the system works as it was designed.

If I shut off the car, I once again have to push the defrost or bi-level button to get the heater to work correctly. It is not a huge problem since I can get the system to work...but I would like it to work as it came out of the factory.

My thoughts are, if there are loose solder connections or if the servo is broken, why would work after pushing the defrost or bi-level buttons.

Thanks
Augusta