Defroster Control ... HOT air only
 

Gents ...

I recently purchased my first MB, a 1989 300e. The heating/ventilation/air conditioning controls seem to be working normally, with one exception ... with the temperature selector wheel set at full cold, pushing the defrost button produces only HOT air up on the windscreen and from the left and right dash vents. The temperature selector wheel, although set on full cold, does not seem to have any effect on the temperature of the air coming out if I adjust it during operation. In fact, the output air seems to be full HOT. Any suggestions on some trouble shooting steps I can take myself?

Thanks very much ...

John Washbush
Heltonville, Indiana

Sounds perfectly normal to me?

x2 - that is normal operation.

Well ... , he said.

I guess that the funny yellow stuff you see now is the egg on my face.

We have some terribly high humidity days here, especially in the early mornings, and it is possible to get the windows to fog up even though the temperatures are well above any need for heat in the car. I wanted to run the A/C to dry out the air but throw the air up on the windshield to speed up the fog removal. I moved the selector to full cold, hit the defrost button and was totally surprised to find serious hot air blasting out of the side dash vents when the temperature inside the car was 60 to 65 degrees. I thought that maybe there was a vacuum operated door somewhere that wasn't opening or closing properly, maybe something associated with the heater. So ... from now on, I will just close off the left side dash vent so I don't wilt myself when I get blasted with the hot air.

Thanks guys ...

John