I have a 1984 300d. I turn the climate dial to the coldest setting. When I turn on the AC on and press the middle climate control button, air is blowing out the defroster/ windshield vent along with the side vents.

I've been in a few other 300Ds and this does not happen. My AC only gets to 60 degrees on a 90 degree day and I'm wondering if hot coolant is getting into the heater core and competing with the cold air over the evaporator.

I'm also confused why hot air blows through the window defroster vents when the far left button is pressed and the dial it turned to the coldest setting. Do the defrost buttons default to Heat, regardless of the dial?

Any idea how I can stop the window vent from blowing air when I press the middle button?

Thx.

Pete