Defrost vents blowing in dash vent mode. ( Help.) - PeachParts Mercedes-Benz Forum

Austin85 · #1 06-02-2017, 12:58 AM

Yes I have done searches and seems complicated enough where more than half owners just sell their cars rather than repair climate control issues. I do not want to have to do this. I'm in South FLorida and having proper AC ventilation is required here. Especially when it's been 96 and sunny for the past week.

Issue: With AC on to blow out of dash vents I get my defrost vents blowing when they should be shut. MY center vents still blow cold air but I guess on 50% power with the other 50 going up out of the defrost vents. My side vents are very weak and I have a rear seat vents behind the console that seems to work the way it should.

I hope this will not require removing the dashboard. I would rather zip tie the defrost vents shut if that's possible than get the dash removed.

My climate control unit seems to not have any effect on redirecting air flow, if this makes a difference... although I am not 100% sure about this as I've really just been concentrating on cold strong AC out of my dash only.

Any input, comments, and suggestions are appreciated.

Austin

Mxfrank · #2 06-02-2017, 07:52 AM

On the Porsche there's an actuator under the dash, about where the driver's right knee is. It's accessed by removing a plastic cover. The plastic connector on the end of the actuator arm is notorious for breaking. It's been a long time since I owned the Porsche, so unfortunately I don't remember the part number.

As for the Mercedes, there is a collection of vacuum pods behind the dash that control the defroster, air blend, leg flaps, etc. It could be a pod or a rubber connector, or it could be the vacuum switchover valve which is also located behind the dash. The defroster pod is usually located roughly behind the ignition switch, and can often be reached just by pulling the instrument pod. If this isn't the case for whatever car you're working on, then the entire dash would need to be pulled. This sounds much worse than it is. I could probably remove the dash on my 190 and have it back together over the course of a weekend. It's just fasteners and electrical connectors, patience will get you through it.

tyl604 · #3 06-02-2017, 08:41 AM

Actually all you need to do on a temporary basis is put something like a towel over the defrost vents. My dash is black and I use a very discretely folded black towel folded lengthwise over the dash vents. Magically all the AC comes out the center and side vents again. In the winter I just remove the towel.

Like you I do not want to tackle the very difficult job of replacing the center actuators.

Austin85 · #4 06-02-2017, 09:12 AM

Plan A is greatly appreciated in such detail and also for my 924S if that ever becomes an issue.
I am going to try Plan B today to see if this simple idea works for me.

Thank you Frank and Ty.

Hit Man X · #5 06-02-2017, 04:35 PM

I replied to you yesterday.

http://www.peachparts.com/shopforum/3715821-post9.html

If you have to replace the center vent. It is not that big of a deal. Start with the three I mentioned.

tinypanzer · #6 06-05-2017, 04:26 PM

Quote:

Originally Posted by Austin85

Plan A is greatly appreciated in such detail and also for my 924S if that ever becomes an issue.
I am going to try Plan B today to see if this simple idea works for me.

Thank you Frank and Ty.

I did two videos on YouTube regarding vacuum pods on w126 cars. Although, in my case it was GenII w126 not a GenI. I believe the pods are the same however, although I do know that the solenoid setup is completely different. At any rate, look at YouTube channel 'hugeshows' and I have two videos... One explains the part and the failure, the other shows the entire heater box outside the car.

At any rate, it's almost certainly a torn diaphragm in one of those pods, or a vacuum leak causing it to not have enough vacuum signal to open. A test with a mityvac will quickly tell you which. It's designed to fail in this mode - defrost is what you want if the diverter flap has to get stuck in one position, for safety reasons.