1989 300SE Climate Control - Air Blowing Out Of The Defrost With AC On
 

After consulting the manual I learned that air should not be blowing out of the defrost vents in conjunction with the dash vents with the AC on (Normal mode). Funny thing is, when I move the temp. control to warm, the air stops blowing from the defrost vents, even as the Normal button remains engaged.

Is this a simple fix or an expensive job?

Thank you for the advice.

You need to perform a vacuum diagnostic routine. This will check for vacuum leaks in the system.

You probably need several if not all of the vacuum actuators replaced. I have only done it myself, never at a shop so I dont know the costs. The parts for the 7 actuators came to aaaaabout $250. A lot of disassembly to get them installed. The rubber diaphrams develop leaks and the system no longer works.