I'm trying to help my friend (really) diagnose and fix a climate control issue with his newly acquired '96 E300D. Here in St Louis, the temps are hovering around 100F, coupled with 300% relative humidity (a joke).

Anyway, when he starts the car and begins driving, the A/C works pretty well, cold air out the center vents and side vents. After a few moments, however, I can hear some squeaky sound from deep in the dash, which seems to be related to door flappers, or CC control valves of some kind. A moment or so later, the cold air no longer comes out of the center vents, but is directed to the defrost vents at the base of the windshield instead. The side vents continue to put out some cold air.

No amount of jiggling, turning off and on, or fiddling with the controls will get cold air to come back to the center vents.

All of my previous experience is with W201's and W116's, which all use vacuum actuators to open and close the CC vent doors. From what I understand, the W210 is controlled by electrical servos and solenoids.

Can anyone describe the most likely cause for this condition (cold air out the defroster ducts, but not the center vents)? I have searched the W210 Climate Control threads, but haven't seen this particular issue described.

Thanks,

SteveM.

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'93 190E/D 2.5 Turbodiesel 5-speed (daily driver)
'87 190D 2.5 Turbo rustbucket - parts car
'84 Dodge Rampage diesel - Land Speed Record Holder
'13 Ram 2500 Diesel
'05 Toyota 4Runner