Barry45RPM

OK. Its 91 degrees here in NYC, and the absolutely hottest air I have ever felt starts coming out of the rear A/C ducts in my car. The air temp can't be reduced in the rear no matter what I do, so I have to shut the A/C System off for the day. The front A/C was NOT able to overcome the extra hot temps generated to the rear so I have to ride with open windows.

Tonight the system works fine. This happened twice this weekend. Anyone know why? Anyone know what I should tell the SA tomorrow?

alewifebp

I've experienced this many times. Was any change made to the set temperature of the rear? While I can't reproduce it, one thing that would occasionally cause it to happen was by changing the rear temperature.

jimbo1mcm

Even if the A/C fails, keep the windows up, because we don't want Camry drivers, etc to think our A/C isn't working.

vettdvr

I would try lower the temp by 1 degree at a time and give the temp control system time to adjust. Allow about 5 minutes between changes. If it does begin to move then move the set point to about 72 and leave it there. My biggest ac complaint is how slow the system is to react to setting change. Jim

Barry45RPM

This is not a normal temperature adjustment problem. It is Full-On Maximum heat from the rear vents no matter what controls are adjusted. Its almost like an electronic hot water valve is stuck open feeding the rear... all the while, the front dash outlets are delivering cold air.

The heat build-up is so tremendous in the rear that the heat bakes your head, and the front seats get unbearably hot. The center console gets very hot around the A/C outlets.

No one would ever or could ever call for this much heat.

Sometimes I wish I was in love with "The Girl Next Door", instead of a Beautiful, statuesque High Maintenance model.

alewifebp

I can also confirm that this is not a normal amount of heat. In fact, since the system thinks that if you lower the temperature, that would naturally mean that you want it to be cooler, it increases the fan speed and delivers MORE heat. Trust me, I've played around with it many times, but at a certain point you just give up and wait till you restart the car. I had a passenger that changed the temp and this happened, and he was wondering what was going on. Since we were all MB owners, we had a good laugh. I have a feeling that the 4-Zone runs on Windows 3.1.

Brav

I have this exact same problem. Also, warm air comes out of driver side front vents as well. Will be taking it in.

Benz-E-r

I just started seeing the same problem this past week and have my car going in next week.

Car is fine in the morning after sitting in the garage all night (and granted it is much cooler in the morning here albiet a humid week). After sitting in the lot at work all day in 90+ degree weather I have cool air (I would not call it really cold) in the front and it blasts hot air out into the rear. Next morning all is well again and on at least one occasion it seemed like after the car sat in a cool area for an hour or so the air was cool in the back, but I did not drive the car far at that point.

I have heard of people having trouble with a gasket going causing one side of the front to blow hot air, I would expect the same would be true for the back. It think the system defaults to routing hot air when the climate control is on, so a problem with the control or gaskets will result in no cold air to a location.

MBenzNL

When te rear only blows HOT air, you can start by closing teh airducts in the B-pillar and center console...adjust the temp for the rear all the way to MAX and then down again...if that doesn't help go to MIN then to MAX and then down again...most of the time that does help.

Underneath the hood is a magnetic valve that controls the hot water that goes into the heater system for the rear outlets - that valve is broken (happens quite a lot on the W211s with 4zone heater systems)...the part itself is rather cheap and fairly easy to exchange...shouldn't take too long at the dealership to get it fixed.

greetingz,

Benz-E-r

As always you have the info! Now I should be able to get them to fix the problem right the first time!

ElDiabloJoe

I have this exact same problem too!!!!

EDJ

Frank Wiesmann

I have a question about this. When this occurs, are the temperature settings in the rear on "hi" heat or at a normal level?

jsloan01

that's a classic post.

good luck getting your car fixed bro!

Barry45RPM

At a normal level. I keep all of them set at 72 all year round and never adjust them.

One thing to understand... This is NOT operator error. It is design error.

alewifebp

EXACTLY! We have all not done something wrong. It works "most" of the time, but it's a real pain when it doesn't. I also keep mine all set uniformly all year round at 68.

During the winter, it was the opposite, cold air coming out of the fronts.

AMGB

It is a value problem just like the earlier post. I just had mine fixed.

ElDiabloJoe

How much for part, how much for labor?

EDJ

Frank Wiesmann

Please let us know what the part was called that you had fixed. Thanks!

ElDiabloJoe

^bump

Brav

mine was recently fixed. will get the PN tomorrow.

ElDiabloJoe

My local independent repair station advised the job would run $450!!!

rukman

This just happened to my today as well. Will be taking car in next week anyway for a scheduled service, but anything specific i shouild tell them to check out?

is there a a TSB for this?

thanks!