w126 vacuum element troubleshooting - PeachParts Mercedes-Benz Forum

4thesporty · #1 07-06-2010, 01:21 PM

I am in the process of ordering parts to overhaul my A/C, however I want to get the pods correct first.

I am losing most of my airflow from my dash to the defrost vents while the A/c is on. Last year I removed the dash and removed the door that controls air to the center vents, that worked marginally at best. Now, I thought my defrost pod could be the culprit so I removed the glove box and tested it and it was good. Here is a pic for those interested:

I then removed the carpet to get to the vacuum manifold ?? This:

I found all but number 2 hold vacuum, and when I unplug number two and hook up a gauge to the black hose I get ~15".

I guess my next step is to remove the center console to get to that pod. Which one does #2 control? Should I replace all while the dash is off?

And, this thing is not coming on all the time, If i tap the wheel it will spin for a moment, then stop. I believe it is the cabin air temp sensor?? Can I take it apart and clean it, or should I replace it?

Also, what is this?

It is hooked to a dummy connector in the foot well.

Thanks in advance!

thayer · #2 07-06-2010, 02:12 PM

I have the exact same issue. So I just left the glove box insert out and closed the defrost vents all the way. That way I don't have the condensation on the windshield and all the air comes out the 4 main vents.

My car doesn't like to turn off when my ACC is set to Economy mode. I'll be following this thread.

The pod could hold vacuum and still not be pulling the vent completely closed.

4thesporty · #3 07-06-2010, 02:27 PM

I'm glad I'm not the only one!

I thing is, sometimes that defrost pod pulls all the way in, sometimes it does not. My thoughts are that the lack of vacuum from the leaking pod (#2) is robbing the rest of the system and not pulling the defrost pod (#1) in all the way.

I just don't know why sometimes it works and sometimes it doesn't.

I think tonight I will leave #2 connected, pull one of the other lines and measure vacuum. As stated when I pull #2 I get ~15", if there is less vacuum from, say, #5 then I think the problem should be with the #2 pod, which I don't know which one that is till I pull the console (radio, PBU, etc)

thayer · #4 07-06-2010, 02:35 PM

Sounds good. Also, the FSM says that when running the acc to cool the vehicle, both in econ and compressor modes, that air will leak from the defrost vents. I have no idea why they did that. Potentially just some german engineer saying that cold air falls and hot air rises. So in the summer we need some of the air to come from the defrost vents to allow the most even cooling. Seig Hiel.

DAVECAD2.0 · #5 07-07-2010, 04:34 PM

Quote:

Originally Posted by thayer

Sounds good. Also, the FSM says that when running the acc to cool the vehicle, both in econ and compressor modes, that air will leak from the defrost vents. I have no idea why they did that. Potentially just some german engineer saying that cold air falls and hot air rises. So in the summer we need some of the air to come from the defrost vents to allow the most even cooling. Seig Hiel.

You are correct. I just replaced all 6 pods on my 420 SEL. All but 2 were shot. Went after them because of windshield fogging. Turns out no matter what mode the controls are set at, it stills always blows some air out the defrost. And here in the "Swamp" (Florida) its a huge PITA. Never need defrost here just defog on occasion. So.............. I fixed the defrost flap in place so that just a tiny amout comes out the "defog" vent and plugged the vac line. Works like it always should have.

4thesporty · #6 07-07-2010, 05:12 PM

Dave, do you remember which pod #2 went to, I should say the second from the top in this pic, the red/yellow one:

4thesporty · #7 07-07-2010, 10:12 PM

Quote:

Originally Posted by DAVECAD2.0

. So.............. I fixed the defrost flap in place so that just a tiny amout comes out the "defog" vent and plugged the vac line. Works like it always should have.

I just re read this post. I'm curious how you made the defrost flap stationary. Honestly, i'm not going to do it myself as I do need defrost in the winter sometimes, but am curious how you did it as it may come in handy sometime down the road.

JeffreyNMemphis · #8 07-06-2010, 03:42 PM

Subscribed... Thank you for the photographs!

I am trying to work out my AC issues. My windshield was moisturized that I had to use the windshield wipers to see last night.

Skid Row Joe · #9 07-06-2010, 03:45 PM

Quote:

Originally Posted by JeffreyNMemphis

I am trying to work out my AC issues. My windshield was moisturized that I had to use the windshield wipers to see last night.

In Houston, even new cars have a challenge getting the windshield fog free in the evening humidity there.

4thesporty · #10 07-06-2010, 04:27 PM

Quote:

Originally Posted by JeffreyNMemphis

Subscribed... Thank you for the photographs!

I am trying to work out my AC issues. My windshield was moisturized that I had to use the windshield wipers to see last night.

Your welcome, if anyone wants more specific photos, I will be glad to take them while I'm in there.

jimandsuzy · #11 07-06-2010, 06:42 PM

The 2 connectors may be for the factory alarm. Most are unpluged because of erratic working.

4thesporty · #12 07-06-2010, 08:30 PM

Quote:

Originally Posted by jimandsuzy

The 2 connectors may be for the factory alarm. Most are unpluged because of erratic working.

That was my first thought, that, or heated seats, which i do not have. I guess since they just plug into a dummy connector under the carpet molding that it is basically an alarm delete?? To my knowledge there is no alarm on this car.

4thesporty · #13 07-06-2010, 09:44 PM

Well, to compound things, I went to the car tonight and now I cannot get the defrost pod to pull shut anymore. I watched it do it repeatedly last night. However, when I pull vacuum from the top (#1) nipple it holds vacuum just fine; they all do except number 2; it will pump up to 20" and slowly fall to 0.

I do get a solid 18" vacuum from all supply lines.

I also noticed tonight that when cycling through the different modes on the CCU when I go from auto to off the fresh air door opens slightly then slowly shuts, is this normal? This is the only time that door opens.

I am thinking that when I get the CCU out I will also check and touch up all solder joints. Need to do some reading on that.

Since I have to drive this car to work everyday I won't be opening up the center console till friday evening for more troubleshooting.

Any comments or suggestions are appreciated.

thayer · #14 07-07-2010, 10:42 AM

The detail you are searching for is in the repair manual. They sell the CDs on ebay for +-20$. I don't have one, but I am gonna go buy one. The vacuum weirdness is pretty tangled in the 126.

Jer · #15 07-07-2010, 10:49 PM

Quote:

Originally Posted by 4thesporty

I also noticed tonight that when cycling through the different modes on the CCU when I go from auto to off the fresh air door opens slightly then slowly shuts, is this normal? This is the only time that door opens.

Keep in mind that there are 3 positions of the fresh air/recirculation flaps: 100% fresh air, 80% recirc/20% fresh, and 100% recirc. This is accomplished with the large-lift and small-lift vacuum elements.