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A/C Evaporator Drain Tube Replacement

on the 1984 300SD (W126)

by bodyart27

(edited by whunter)


Just got back from a road trip to Houston (from Dallas) and when unloading the car last night I noticed the carpet behind the driver's seat (where the rear floor mat lays) was saturated. Real wet. Pulled back the carpet and put a fan in the car overnight (still damp this morning). Not rusty - had to be recent.

Hmmmm. I opened the sunroof and poured water into the rails on both sides (poured in the middle). Car took a pee onto the pavement from the rear wheel wells. Drains were not clogged. That seemed right.

I got nailed in a rain storm in Houston driving in on Friday, and overnight sitting in a parking lot. Maybe a door ajar? Window cracked? Water forced in somehow?

Initial look at the trunk - looked dry. I can't recall anything (like a water bottle) that could have leaked back there.

If water came in on the back edge of the sunroof - where does it go?

Can condensation from the A/C get back there? the front floors / floor mats are dry.

Any thoughts? Something to look for? I guess if it only does it once I'll rack it up to a door/window ajar?

But, long story short, I pulled the panel back, found the A/C evaporator drian tube easily and installed it. The old tube had deteriorated to the point where I could see the inner coil spring that is inside the foam of the drain tube (inner spring is there so it doesn't collapse as there is a wiring that crosses over it). I really think this could be designed better. But, then again, it lasted 23 years. If you click the "buy parts" link and look up a/c evaporator tube you'll see what I'm talking about.
Click Here for Fastlane Link

So finally got some time to add some pics.

First pic is just the new A/C drain tube. Very odd construction - not too impressed, but the original did last 23 years.

Inside the spongy foam tubing is a spring that prevents it from collapsing.

There is a wiring harness that goes across the tube, so I guess the engineers wanted to be sure there was no condensation on the outside (thus the spongy foam).

Old and new drain tubes

As you see in the pics:
1. You remove the kick panel and knee bolster (the panel that goes above your knees under the steering column) to see the drain tube, not too difficult. image

2. There is a wiring harness that is strapped with a reusable zip tie over the drain tube, I suggest unplugging the top connector and loosening the zip tie to make it easier to remove the tube.

3. There is an ivory colored ring clip at the top of the tube, the tube had deteriorated so much that I just pulled it off the connector at the top, clip and all, then I undid the clip (hinged on one side, just a hook clasp on the other).
4. The drain fitting on the A/C evaporator has a little lip (like on a radiator). The clip goes past the lip (like putting a hose clamp on a radiator) so the tube won't back off.

5. You thread the tube under the wiring harness and poke the rubbery end into the transmission tunnel.
That's all there is too it.

The Mercedes Benz evaporator drain part numbers are:

LEFT MB# 126 830 11 96

RIGHT MB# 126 830 04 96

I have had some wood blocks under the carpet to get the SD to dry out. So far so good!

Discuss this DIY here.


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