zafcom

Hi all, I have an issue that's driving me mad (especially in winter )
I own (and love) a 2007 E220 CDI (S211) Classic.
Some months ago I started noticing that the central vents located in the front (above the radio unit) somewhat stopped blowing the usual warm air (it was cold outside), letting in an abnormal flow of cold air. By "cold" I actually mean COLD, not just "a little lukewarm" or so on.
Asked 5 different MB dealers, and had 5 different answers, but mostly "oh, they're meant to do so".

Now, I drove this car for the past 4 winters, so I actually KNOW those central vents are made to blow the same air the other vents do (I remember VERY well putting my hands on them while driving back from work in December, and feeling grateful it went warm so quickly), so no: it's not normal.

After some months I convinced myself and yesterday had it "repaired" by my local MB dealer / repairer. I was charged a small sum for a "butterfly valve reset", but after much reassuring that the problem "should be fixed" I noticed little to no change at all.

The symptoms are (Auto mode ON unless specified):
- After engine start / warmup, central vents blow warm air, at the very same temp as side vents do. Top, bottom and rear vents do the same.
- After some KMs, center vents start becoming increasingly colder. Lukewarm at first, than cool, than damn cold.
- Cold air intake is stronger on the left (driver) side, a little less strong on the right side. Both vents blow in more air than side vents do.
- In the meantime, the side, top, bottom and rear vents continue their normal heating.

TESTS performed:
- Auto mode OFF, "front vents only" mode active > side and center vents finally blow WARM air (but the lowest part of the central vents still blows cold air, as if unmixed)
- Auto mode OFF, all other vent modes > central vents STILL COLD
- Auto mode ON, temp set to MAX on both knobs > central vents STILL COLD.

On another MB forum I read someone swearing this is a typical behavior from a faulty Changeover valve.
BUT reading this MBworld post I always read of people having always cold / always hot air, NOT center / side.

Those who have right side hot / left side cold have a coolant level issue, but my coolant was replaced just hours before I noticed this issue...

Please, help me troubleshoot this problem
I have no StarDiagnosis, and I really don't know where to search for.
Is it a Heater Control Valve issue? Or is it just some malfunctioning flap? (which one? I hear absolutely NO noises...)

konigstiger

Dealer repair attempt should have included pulling stored fault codes with MB DAS, check invoice. May be actuator given normal start and eventual malfunction, attachment covers actuators.

Nikola T.

Hi I have exactly the same problem. Heater exchange valve was replaced, but from center dash vents still blowing cold - TO COLD.
If I switch to manual heating and select mode to upper part then it is heating also in central part!?
Zafcom, how you solved your problem?

Overheated

KT...are you saying the codes must, or should, be re-set when the heater valve is replaced? I replaced mine and works fine, no codes.

Perhaps it's his heater core?

Nikola T.

I checked with Xentry all flap motors.... all tests are OK. No error detected on AC unit!?
Also when in Automatic mode (AC is OFF) from center vents on dash cold air is blowing. I think it is air coming from outside because some of flaps are not properly aligned.
With Xentry I also started all tests and teach-in procedures which could set travel of flaps within air distribution unit.
I still didn' found the cause or solve the problem. Rear center console is heating, but I think it used to heat more in the past.

dudaronamous

My impression is that AC is designed to be “always on”, and that when AC is in off position you are just getting outside air vented into the car (Not 100% sure about this). Does heat work when AC is ON?

Nikola T.

I would say all heating is working just fine. ONLY FROM CENTER VENTS above radio is blowing always cold, except first few minutes after start of cold engine if outside temperature is below freezing 0°C. Just like Zafcom reported.

Heater valve is new.
Auxilary electric circulation pump is working.
No error code with Xentry diagnostics detected.
Flaps seems to work OK
Temperature sensors (top and near ingnition key) are sucking air properly, but can't say whether they are accurate.

More likely would say that air is trapped in central heat exchanger or clogged ??
I would like to know the cause and solution if somebody SOLVED the same problem.

mildenbenz

Me too. I noticed the same on mine but thought it was normal till I ran across your post. Manually I can get the heat out of the center upper vents. But it goes back to cold when switched to auto.

BenzClass

My w211 station wagon started doing this a couple of months ago.
Has someone been able to find the cause and the solution?