Why foam? - PeachParts Mercedes-Benz Forum

okyoureabeast · #1 12-22-2009, 09:22 PM

So I discovered that this foam tubbing under the dash which i believe is called the aspirator tube ruptured and a small hole formed causing my heat to be wonky and all around not warm (heat only on max and while accelerating).

I'm happy I discovered this and it wasn't something more costly like the monovalve or the aux water pump.

However I am kind of befuddled why MB decided to use a foam tune there instead of just joining the two rubber pieces together.

Any particular reason why they did this? I'm reading around and no one seems to know why.

I'm replacing it with some rubber hose for a windshield washer line.

aaa · #2 12-22-2009, 09:28 PM

Wouldn't be the first time somebody did that.

shadetreemechan · #3 12-23-2009, 07:57 AM

The foam acts as an insulator to help the temp sensor react more quickly to changing cabin air temps. With the rubber hose you will find that your temp regulation has more delay because the rubber will heat or cool slightly the air as it travels to the temp unit.
I have replaced mine with clear vinyl hose and It works ok, just slow to respond.

dablk1 · #4 03-29-2010, 11:37 AM

Where is it located and how do I access it? 1991 300D 2.5 turbo

Biodiesel300TD · #5 03-29-2010, 11:46 AM

Quote:

Originally Posted by dablk1

Where is it located and how do I access it? 1991 300D 2.5 turbo

Not sure you car will have it. He is talking about a 123 chassis 300D. But they are directly behind the glovebox in the 123's. So if yours has one that is likely where it is.

I found mine in pieces when I pull my glovebox. I too put a piece of vinyl hose on it. shadetree I like your explanation. It make sense.

dablk1 · #6 03-29-2010, 12:14 PM

Thanks for the rapid response. How do I pull the glove conpartment?

vstech · #7 03-29-2010, 12:33 PM

... does the 91 D have a glove box? my 93 has a console storage, but there's an airbag where the glove box is on a 123...

dablk1 · #8 03-29-2010, 12:36 PM

Yes, it has a glovebox. It only has driver side airbag.

babymog · #9 03-29-2010, 02:14 PM

The temp sensor is in the overhead / dome-light assembly.

aaa · #10 03-29-2010, 04:59 PM

With a (rubber) tube that goes all the way from the dome light to the evap box. And a miniature fan too I believe, the 123 didn't have that. The aspirator fan's behind the glovebox.

polarisrmk · #11 04-01-2010, 02:22 AM

Does anyone know the sensor configuration on the 126? I have an 85 SD and my car is cooking me out with the heater on and doesn't regulate the temp. Or as my friends call it "unclimate control"

bmwpowere36m3 · #12 04-01-2010, 09:41 AM

The problem with Shadetree's explanation is that the sensor itself is located right at the duct opening for the air temperature sensor (plastic grill on the dash). The long tube to the blower motor is only used to pull air from the cabin across the sensor. By the time it reaches the foam tube section it has long since passed the actual temperature sensor.

If anything I think the foam acts part as a strain relief, allows for some expansion and contraction, and second offers some heat insulation (but why isn't the whole tube insulated?). Then again, this is how my ’81 300CD is configured, but I doubt any other W123 with ACCIII is different.

LUVMBDiesels · #13 04-01-2010, 10:38 AM

When I did the hose in My '81 300SD I used a piece of foam pipe insulation. I simply used E tape to wrap it so that it would not split open and it looks like the factory hose. I never thought of using just a piece of rubber hose... I THINK that on the early W126 the sensor is located by the air box and not up by the opening in the dash, I do not remember too clearly though...

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