Kabra

Wondering if any other W212 owners have the problem of cold air blowing out upper vents when it's cold outside. This is in the Auto setting and system should be in heater mode.

Typical scenario is start car up in morning. Interior warms up as it should and then at some point I keep getting very cold air (Low to mid 50s F) out the dashboard vents right on upper body and face.

It's at the dealer and they claim everything is working fine but it's not. I'm going back Monday morning to drive it with the shop foreman so I can show him. Just wondering if anyone else has this problem or any insight into it?

KEY08

I know the W211 had issues with the heater control valve. I have not heard of any of the same with the W212, but maybe yours is faulty. I believe there are also blender doors that may not be functioning properly in your car.

Kabra

Interesting about the heater control valve. Do you recall what the problem was that people were having with it?

KEY08

Sure, the control valve was not diverting warm coolant to the heater core. The valve itself stopped opening and closing. It was like a $60 part. Once replaced, all went back to normal.

lovemymercedes

I have the same in my car, there is only 100K KM on it, it works beautifully for 10 minutes then I start having cold air, I took it to a local mechanic , did scanning but didn't show anything, changed the thermostat but didn't help, would appreciate it if you figured it out what's wrong with your car

Kabra

I'm just waiting for it to get colder outside and take it back to the dealer. Then I can show them for example that it's 48F outside, temp set to 70F and the A/C is blowing 45F air on my face. They also did the scanning but couldn't find anything. But that was in summer when it was mid 60s so it wasn't compelling. I'll certainly let you know how it all turns out. Shouldn't be too much longer.

lovemymercedes

Thanks for your prompt response, and I'll let you know at my end if I had it fixed.

Oda112

It might not be an issue with it whatsoever, and I'll explain why: the automatic climate control will regulate the airflow in such a way to keep an overall constant previously requested temperature. Usually, when the temperature outside is lower than the one requested by the user it will blow warm air in the footwell and not so warm (sometimes cold) throgh the mid/face vents and windscreen vents. This is to not make the driver drowsy over long driving trips. On some vehicles, you'll have the color coded wheel between the two center face vents and you can change the temperature of the air coming through those, but on the W212 that wheel doesn't exist. In my experience (I own 3 cars with automatic climate control) the air blown through the center vents will always be perceived as colder than the air blown through the other vents. I would get concerned if the footwell air is cold when the outside temp is lower than what you've requested via your climate control buttons, or if there is no perceivable temperature difference between the inside of the car or the outside.
One way of testing your climate control operation is to take it off auto mode, make it blow air only through the mid/center vents and have it set at the highest temperature possible. Do this when the engine has reached operating temperature, and wait 2 to 3 minutes before measuring the temperature of the air, if it's still cold then you have an issue.

Kabra

You may be right that it's all by design but if that's the case I'd say it's bad design. First of all the passenger side has the same problem so that would argue against the keeping the driver awake hypothesis. Also in that regard, the air gets so cold I turn the vents off which would again defeat the driver alertness idea. The temperature of the air coming out of those vents is really cold, often in the mid to high 40s (F). As my baseline for comparison are two 5 series BMWs that I previously owned and a Toyota Tundra that I currently have. Those vehicles all work wonderful in this regard. That's why I feel that either there is something wrong or it's bad design. This is the one thing I really despise about this car and it needs to be resolved one way or another.

Oda112

If it's too cold then you have an issue. I was driving my W212 yesterday, the temp outside was around 60 and the one I requested inside the car was 74. The air blown through the mid vents was feeling cold but overall, the whole car was warmer than what was outside so I was comfortable. I have a E60 530xdrive as well and it behaves similar. Maybe both of my cars are broken somehow, that's a possibility too.

Arrie

You say the car first warms up so first it blows warm air. When it blows cold does it also blow cold in the foot well areas too?

mnje350

Ahh I think he is stating that the ENGINE warms up quickly yet the ventilation system blows cold air.

mnje350

OK, reread OP’s post so I should not have commented on Arrie’s reply so quickly, sorry Arrie. However, once the climate control system warms the cabin, there is always the effect of the solar heating that the sun sensor detects and it may be trying to compensate for that. I just direct the vents away from me and the problem goes away. Cabin is comfortable and I don’t have the vents blowing in my face. This is common in NC where we can have cool mornings but the solar heating is intense in the car. Just my .02 worth.

Arrie

No problem man, but I don't really believe to the sun effect on this unless the OP's car gets really hot while it is blowing cold but he does not state that.

But I have a scenario here that could explain the problem. This is very weird but it happened to me with one of my previous vehicles the 2004 Chevy Tahoe. This happened to be our Independence Day in 2010 so it was not about blowing cold in cold weather but it can still explain the OP's problem.

So, going to get fireworks and I get "Engine Coolant Temperature High" message in the cluster. The temp gauge went to red indicating the same. I pull over and check the coolant level in the expansion tank and it is between the Low and High marks much closer to the High mark. I drove the car about 10 more miles and the condition stayed the same and I decided to check the coolant again and pulled in the parking lot of an AutoZone. The expansion tank was at the same as I saw it already earlier so I checked the level in the radiator. After removing the cap with all precautions as it was hot I came to find out there was no coolant to be seen in the radiator. I went in the parts store and bought a gallon of antifreeze and poured it in. Still could not see the level. Went and got another gallon and poured almost all of it in, only about a cup did not fit. The coolant was almost two gallons low yet the expansion tank showed correct level and this is why I did not get the low coolant level message as the level is measured in that tank and level there was fine.

I later learned that these trucks had a problem with a "porous cast" heads that allowed coolant to leak internally inside the engine to the intake and was burned so there was no coolant dripping under the car. In my case there had to be a faulty valve in the radiator cap not allowing the coolant to flow from the expansion tank to the radiator so the level did not drop and so no low level message.

So, to the OP's case. If the car first warms up it means the heating works but then after a while it starts blowing cold. This can be caused by low coolant and I have experienced this with my old pick-up truck. With low coolant there is no adequate flow thru the heater core as the thermostat opens to circulate the coolant to the radiator. When the car first starts the thermostat is closed with only a small weep hole to the radiator. Almost all coolant flow is directed thru the heater core and this allows the car first to warm up until the warming coolant causes the thermostat open enough so that due to low level there is not enough coolant to flow thru the heater core any more. Result is cold air blow.

This condition also explains why the dealer service says everything works fine. They do not check the coolant level in the radiator so if there is a faulty cap not allowing flow back in the radiator it can cause low level and it does not show in the expansion tank. And, of course, everything electrical is fine and they cannot find the problem.

If I was the OP I would check the coolant level in the radiator. I assume here that these cars have the radiator cap like other cars with the two way valve have it. I would not think the plastic expansion tank and the rubber hose to it are strong enough against the cooling system pressure during operation.

belarus27

So was this the water heater valve (same issue that was with w211)then?
have had this for a while , never paid too much attention to it.

i can only feel the heat when its about 80-HI(actual heat is at 84 or HI though) , lower than that all feels about the same , kinda warm/not so warm air coming out from vents.

kajtek1

First time I read the topic and did not try to get every word, but here are my experiences.
1. MB expansion tanks are working under the pressure and coolant flow via them all the time, so if you see coolant in it, that means radiator is filled.
2. center vents on MB have been always blowing cold air only. Not sure if they changed it on W212, but since the design is like 100 years old, I don't think so.
You have air flow control on the vents. Use it if you are not comfortable. I drive in warm weather year around (actually it was freezing 47F this morning) and cold air in the center never bother me.

belarus27

yea it was 43 in CA as well.

so if i close my center vents , i should be getting warm air just from the outter 2 vents? Need to try that , it might work. I was already thinking about changing that water heater valve, if its gonna work like this , i might be able not to give a crap about it for now.

KEY08

Center vents on the W212 and W211 blow warm or cool air depending on your control setting like any other car brand.

Arrie

+1
If I set my temperature up so that heating is necessary in AUTO mode the warm air starts to blow from floor vents. When I give it one click up on the MODE BUTTON the hot air will switch to the center wents.

KEY08

Yes, exactly. The W211 did have an additional control in between the two central dash vents which allowed you to introduce outside air to those two vents. I believe this was a hold over to the MB philosophy of having cool air year 'round to blow on your face for whatever reason(to keep you awake?).

El Cid

Just found this topic. For past year I have experienced something similar, but mainly in spring and fall. Keep the auto temp on 68, but if outside temp is in 50's, cold air blows out of upper vents. Dealership did their magic computer check and No Faults Found. So no problem.
May try just using manual setting and see what happens. Right now, I just turn off or greatly reduce airflow from upper vents. It does blow warm air out of footwells.
I know from previous cars that all systems are likely to blow cooler air out of upper vents to keep driver alert and maybe to help with keeping windshield and side windows from fogging up.

pezzy669

Mine does this as well but only in the weird in-between fall and winter temps (typically 50-60 F outside) where it may be warm to hot standing directly in the sun out but still a bit chilly in the shade - I equate it to the bi-level mode in old GM's where it would pump cold air to the vents and heat to the floor. While its logic is great I would say 60% of the time it worked well to keep my sun-drenched upper half cool, the other 40% of the time I was turning the vent away to not blow right on me or fiddle with the temp settings to stop the bi-level mode.

Similar to above these are the only times I find the auto not working to my liking - during every other extreme (cold or hot) it works flawlessly. I think the mild in-between temperatures is where it might be programmed to the 80th percentile so is not going to make everyone happy.

Kabra

I'm the OP and like you guys I also find it to be much more of a nuisance during the colder months. I never got anywhere with the dealers and my '14 is out of warranty now. The dealer's argument was that the temp inside the car can become elevated from sitting in the sun even on cold days. Yeah but it shouldn't be blowing 47* air on you when it's 38* outside (or whatever). I think it might be a blending issue where the dealer may be correct that the cabin needs cooler air but that air should be blended with warm air so it's not blowing ice cold in your face. The '05 BMW 545 I had before this Benz worked well in that regard, as does my '08 Toyota Tundra.

El Cid

This is pretty much my experience as well.
I guess the real problem is that we expect or want the automatic HVAC in a car to work the way a thermostat in a house works. Bottom line, it's a car and what with the roof, sunroof, windows, etc., there is a wide temperature variance inside the car.
Anyway, thanks for help.

kajtek1

No, not me. Household HVAC is design for keeping the temperatures with low variations, while working most of the day. If you shut down heating going for winter vacations, on your return the house can take more than 6 hr of constant heating to bring interior to comfortable temperatures.
In my cars I often enter the 150 F interior. Takes really just seconds to have cold breeze into my face and just couple of minutes for the interior to be bearable.
For years MB was making center vents "cold air" only and I think starting with W211 they do get some heat.
My wife does't like cold breeze and when I don't let her play with thermostats, she turns louvers into the ceiling. Problem solved.