On my '85 300D whenever I have the climate control pushbutton pushed so that the air will be directed to the windshield, I only have hot air. It doesn't matter if the temp control is set to cold. On rainy muggy days the inside of the windshield will get fogged up and I've always used the defroster/defogger setting to clear it up. However, since this is my first Benz I was wondering if maybe the tmp control is disengaged when that button is pushed.
84 500SEL EURO 87K
85 300D 267K (and still goin' strong)