Greetings,

Somewhere from the late 70s into the early 90s MB used a 5-button with red/white/blue thumb wheel as the the climate control unit (CCU). The air is then directed to either the feet, defroster, center and/or side vents. The w210s and later w140s I have seen have a newer unit with separate left/right settings and an LCD display that often fails.

I was in my friend's w140 yesterday and when I turned on her car air was being discharged from her various vents including her center vent. That got me to thinking, "I can't remember air coming out of my (the older 5-button CCU) center vent unless I put the temp wheel on min and the push-button on EC."

Are there other settings/conditions that result in air being discharged from these older CCU besides the one setting I describe above?

Thanks.

The center should be cool air like ac or colder temp on the ccu

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hum.....
1987 300TD 311,000M Stolen. Presumed destroyed

The center vent should open anytime the car is being cooled, whether the AC is switched on or if the system is in EC mode.

On a 124 if you only got center air when set to maximum cold, it indicates likely failure of the center vent vacuum actuator. The 124 has a 2nd "diverter" door that admits air to the center vent under maximum cooling conditions. When this opens, you got some air.

And more specifically, in the W123 and W124, you do not ever get heat out of the center dash vent unless you modify the plumbing to keep the center vent open all the time. This I have done and it works great.

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

I've already modified my system such that it always runs on partial recirculated air by permanently applying the vacuum to the main chamber of the "recirc pod". I think I'll do the same mod that Jeremy has performed and also connect the pod for the center vent to permanent vacuum as well.