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You've been a busy bee.

I can't wait to see more.

Can you show us via picture, of where your evaporator failed ?

Please see my post here:
WTD: current W124 BEHR evaporators pics: no more dissimilar metals ?

:-) neil

I do not have convincing proof that the evaporator did fail. The best pictures is Pic147 and that doesn't show a leak. I found a large amount of dust on my evaporator when I replaced my blower motor about 6 months ago. I had had an ongoing leak from my AC which the dealership could not locate. Then I noticed that the heating in my car had also become weak, seemingly due to low output from the blower. All this made me think that the problem was the evaporator - a leak in a place where the dealership would not look, compressor oil leading to buildup of dust on the evaporator, and consequent poor heating output due to low airflow that did not improve with the new blower motor and vacuuming because of dust lodged within the fins of the evaporator.

It turns out my reasoning was faulty. After putting the new evaporator in and partially reassembling everything, I checked my airflow and found that it was still lousy - plugged evaporator fins were not to blame. I then opened up another of my cars in which the airflow was relatively good but in which the blower motor would occasionally not start. In that car, I suspected that the brushes were to blame since the voltage to the blower motor regulator was normal (I have 3 of the same car so that I can compare and contrast them). My plan was to replace that blower and use the broken one in this car to test whether perhaps just the blower motor in this car was weak. However, it dawned on me once I looked at the failing blower motor in the other car which had decent airflow that I had installed the new blower motor in the car in this post backwards 6 months ago. After placing the blower motor in this car in the correct orientation, I got the good airflow I was looking for. The mistake occurred because 1) the mercedes instructions did not note orientation as being an issue, 2) I have become used to all parts from mercedes having some mechanism to prevent reverse installation, and 3) the acm blower that I installed had the electrical connection on the opposite side as that of the original Behr blower.

Finally I put the new blower in the other car and found that the little bit of vacuuming I had to done on that evaporator resulted in a noticable increase in airflow. I have attached pictures of the dust before vacuuming on that car.

To summarize:
1. I don't know for sure that my evaporator failed.
2. In my experience vacuuming even a moderate amount of dust off the evaporator improves airflow.
3. It is easy to install an ACM blower backwards and significantly reduce airflow.

None of this is included in the original post because it had little to do with the "how to replace this" nature of the post.

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1991 300TE 4matic 205k miles (bought 2000)
1992 300TE 4matic 200k miles (bought 2000)
1992 300TE 4matic 150k miles (bought 2004)

Funny, the first time I replaced the blower with the ACM unit, the same thing happened, but I caught it right away, before bolting everything up.

The ACM blowers don't have a "polarized"/"keyed" mounting like the BEHR, so you need to take a picture of the blower-fin orientation to remember which way to install the ACM unit.

:-) neil

I am preparing to do the evaporator on my father’s 95 E300 in a few weeks, so I very much appreciate the time you took to post the details of your work!!

I also did battle with an aftermarket blower in my 300TE, and had to modify it's mounting bracket to get it to fit, but I checked it powered on before I reinstalled everything. Bummer that it bit you.

I have the 124 service manual and CD, and have been bookmarking relevant threads as I see them. Your’s will be the first I print out- many thanks in advance.

Dave

Thank you for the pictures. They have been helpful for reference. My 1992 300TE has a leaking evaporator, and other A/C leaks, which this is the first time I have done this job. It is a good learning experience without breaking everything.

David, this is an incredible write-up! Very Impressive.

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2012 E350
2006 Callaway SC560

Here is a pic of the evaporator leak and evaporator/heat core assembled.

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This is a great post. I wish I could find detailed instructions and photos for other repairs like removing door panels, for example. But I can't believe you did all that work, practically dismantling the whole car, it seems, only to find the evaporator was most likely not the problem. Thanks for the note about the blower being able to be plugged with reverse polarity. I will keep that in mind if I ever have to replace it. This also sounds like a good lesson in why to replace the cabin filters on a regular basis.

Many thanks for taking the time to do such a detailed summary of the repair.
In fixing a baulky blower motor on my 92 300 TE4 I found a wet evaporator so will be undertaking this same repair soon.

Jim Cross

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92 300 TE 4matic