Climate Control Question - PeachParts Mercedes-Benz Forum

willrev · #1 01-06-2005, 11:32 AM

I am trying to diagnose what is wrong with my climate control. Last Summer when I pressed the button just to the left of the EC button, I got recirculated air through the center dash vents. I started having intermittant problems with air flow coming out of the center dash vents. You could hear a door or flap closing and opening in the dash and when it did, it changed whether or not air would flow through those vents when cooling. Now, when you get into the car after it sits all night and start it up, you can hear a flap either open or close (pop sound) in the dash. Air is constantly flowing out of the rear seat vent in the center console, but will not blow heated air. Owners manual says it should blow heated air.

I am wondering if the vacuum pod that controls fresh-recirculate is stuck open and this is why I am not getting air out of the center vents when in air-conditioning mode and also why cold outside air is blowing in console vent into back seat.

TX76513 · #2 01-06-2005, 11:47 AM

You are going to have to look at (diagnois) the vacum pods and diaphrams that operate the flaps. In regards to the center console vent - in my SDL it does not produce heated air. If you have the repair CD for your model there is a good troubleshooting section on the ACC. Is the problem on the SD?

Here is a link that may prove helpful CCU

jbaj007 · #3 01-06-2005, 12:30 PM

The vent to the rear seats at the very back of the center console should only blow outside air or cooled air, never heated air. In winter it is closed with the little lever on the vent grate. Heated air for the back comes from vents under the front seats. FWIW

willrev · #4 01-06-2005, 03:02 PM

Quote:

Originally Posted by jbaj007

The vent to the rear seats at the very back of the center console should only blow outside air or cooled air, never heated air. In winter it is closed with the little lever on the vent grate. Heated air for the back comes from vents under the front seats. FWIW

You are absolutely right and I realized this after I re read the owners manual. My airconditioning does blow out of rear seat console vent.

I don't seem to get much heat on my feet in the front. My feet stay cold. My air conditioner is really cold air, but it should blow out of center vents and doesn't. This is what I am trying to diagnose. Heat is not supposed to come from center vents. It does not in mine. I am basically getting no air from center vents.

I am guessing it is the fresh air - recirculate air vacuum pod but am not sure. I am wondering if anyong else had this same symtom on a 300 SD.

ytr1903 · #5 01-06-2005, 03:40 PM

Willrev,

I am no expert on this subject, but my 300SD is also not blowing air through the center vents. Here is my take on the problem. The recirculation pods aren't directly related to the center vents, in other words, whether the recirculation door is open or not will not affect the operation of the center vents. The recirc door can be either open or closed and the center vent will blow cold air, if the correct buttons are pushed and correct ambient temperature is present. There are a number of possibilities for diagnosis. One, the center vent pod, which is located directly behind all the pushbuttons, has a bad diaphragm; Two, the switchover valve that operates the center vents is inoperable; Three, there is a major vacuum leak elsewhere, that prevents the center vent pod from opening because of lack of vacuum; and Four, the pushbutton unit has gone south. In my case, the recirculation pods have major leaks, thus preventing the center pod from opening. (If I close off the vacuum to the recirc pod, then the center vents will open) I have ordered new pods from Phil today. I hope this helps and if I have written anything that isn't factual, I am sure that someone will correct me.

Tom

PS-In re-reading your question, I hope that I have addressed your problem at all. Good luck!

TX76513 · #6 01-07-2005, 08:22 AM

When I replaced my CCU my center vents started working again

It is a PIA to work on these things (diagnois) but if you use the troubleshooting chart step by step you can figure these things out. All in all they are great when working properly.

side bar - if anyone needs a CCU pushbutton I have one # 126-830-02-85 various years SD and if I remeber right some years 560SEL.

SD Blue · #7 01-07-2005, 12:18 PM

Quote:

Originally Posted by willrev

.......I don't seem to get much heat on my feet in the front. My feet stay cold. ........... My air conditioner is really cold air, but it should blow out of center vents and doesn't. ......... I am basically getting no air from center vents.

I am wondering if anyong else had this same symtom on a 300 SD.

Will,

I am having the exact same symptoms on my '84 SD. After troubleshooting with a mightyvac, I found that the vacuum elements for center flap (center a/c vents) leaked like a seive and the footwell wasn't a whole lot better. About the only thing that worked real well was the defrost. The fresh/recirc. worked fine (this can be viewed by pulling the little plastic plug inside the glove box and a flashlight) (this is also where I use "air freshener"

)

My determination was that most of the vacuum pods needed rebuilt. Here is a link to a guy who carries the replacement diaphragms and a little tool with instructions: www.autoluxmbz.com When you order, tell him the model of your car and he will send you a complete kit ($65 incl. shpg) or a selection if you prefer. Fortunately, on the W126, the pods are fairly accessible.

Hope that helps,

Sam

dannym · #8 01-07-2005, 01:18 PM

I get air out of all my vents at all times.
When in heating I get cool air from the center vents and rear seat vent. All the other vents blow heat.

when cooling it blows cool air from every vent.

Just another thing to check when I get the time. Wish I had a copy of that troubleshooting chart.

Danny

willrev · #9 01-07-2005, 02:25 PM

My climate control unit seems to work fine. It cuts off and defrost kicks in well. The auto function works well. When the problem started, you used to could punch in the last button to the left before the full defrost button and the center vents would start blowing. Then if you switched it back to the normal air conditioning button the center vents would blow. Or if you punched the button in right after you immediately started the car and it had not built up a lot of vacuum pressure yet, it would blow from center vents, but if you waited, to punch it on, then they would not blow air.

I really think it is the pod on the center vents. I just don't know where this one is or how to take my dash off to get to it.

I think it is right behind the vents under the dash cover.

ytr1903 · #10 01-07-2005, 04:10 PM

Willrev,

The center vent pod is right behind the pushbutton unit. Take out the ashtray, radio and pushbutton unit and you will see it in the upper left corner of the hole you just created by removing the above. That pod can be checked at the bank of switchover valves. It is the valve labeled #3. Pull off the vacuum hose and apply vacuum to the hose going toward the pod. If doesn't hold vacuum and you don't hear the door open, you have found your problem.

Tom