AC blowing on windshield, climate button problem
 

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

Can't give an anwser about the vents. As for the temp, try checking at the MONO valve (if you have one on a 123 car). I had the wires unhooked over the winter, and this spring had warm air coming into cabin when running A/C. Plugged wires back onto MONO valve, and had cold air again.



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1984 MB 300 SD Turbo

Welcome to the forum.


The system has a series of vacuum operated "pods" that move the air doors.

When the diaphragm fails in the pods, the doors don't move. In the case of the defroster door, it's default is OPEN. So, if the pod has failed, the system can't close the defrost door and you'll get full defrost in all modes. The problem can be the pod itself, or it can be the electric switchover valve that controls vacuum to the pod.

In the case of the defrost setting, the system sends full heat and full blower to the windshield.........regardless of ambient temperature. The a/c compressor is also engaged to dry the air. Nobody can leave the system in full defrost for more than one minute or so. It's not the best of designs.

I also have a problem on my 96 E-320 with AC air blowing on the driver side windshield vent only. The pod box with all the vacuum lines operating from it seems to be fine. At least upon opening and checking oms, they were consistent. When you hand pumped the vacuum manually the vent closes. Does the climate control for each side have a heater sensor valve somewhere for each side. Could this be whats causing it to only blow on the drivers side glass only. Other than that it blows out of all the vents as normal operation would have it, with low blow from drivers side vent by the door.