Done in again!

My beloved movable chair, the 96 S 420 in the garage, has done it to me again! Took it to ole smilin sam who replaced the leaky evaporator. Since that replacement, the cooling stops after driving for 90 to 120
minutes. Turning the compressor off lets things melt or cool down or something and the ac will work again after 15 to 30 minutes go by. Suggestions included low freon (or that new stuff that does good things to the atmosphere when it leaks out) or a bad or missing or improperly reinstalled evaporation temp sensor. So Ole Smilin Sam checked the fluid and found it 0.5 lbs low. He thinks that may have been causing the problem. But that would not explain why ac screwed up the first time I drove it anywhere after the new evaporator was put in - trip took place within a week or so of the repair. I asked Smiling Sam about the temp switch, but he ignored the question. He says that something is probably heating up. And ole growly cookie monster who runs the office suggests that it could be the temp control switch. They did have to keep it a second day, so perhaps they did go in on the left lower side of the dash behind the gas pedal to fix the evap temp sensor, but I think they would have mentioned that.
So now my question is - can any of these things be tested?
If so, I may consider visiting Heavy Carl, the local stealership. They will charge at least $100 to test anything, of course, and then minimum $1000 to repair it. But this may be cheaper to do than to buy the current 5.5 gas eater version of the new computerized S Klass. And if I can't get the thing fixed, I will have to buy a different car before April, probably a used Kudzu Kar cause the new Kudzu Kar is koming out this fall.
mcbrue warminguply under the bridge in the trailer down by the river
96 S420
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Sorry to hear that the saga continues with the S-klass. Heck, this one has been goin' on for longer than "Gone With the Wind" (perhaps we should call you "Rhett" and your car "Scarlet"?). While I'm not sure if it will help your specific diagnostic I did find a really nice article on how to get diag codes off of the 124-model console. It does have some information that seems to be very similar to the problem you described with the evaporator temperature sensor.
https://www.continentalimports.com/ser_ic40142.html
Josh
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Josh wrote:

Wow, great article, the earlier one applies to my 124 model though:
https://www.continentalimports.com/ser_ic60046.html
The Kilma A/C controller module was intermittent, and was having the symptom where the A/C would be fine for 10-15 minutes before the compressor cuts out, also seemingly at random.
Wish I had seen the article, would have made me less mystified.
Working well after replacement.
Cheers, WS
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What a great exposition on M-B A/C diagnosis and repair! Very well written; this fellow must have a PhD in the subject.
The other side of the coin is M-B's calculated effort to cheapen the components' quality as they raised the system's complexity.
That approach is what's now - years later - biting them in the ass and encouraging us owners to look elsewhere for new cars.
Suggest Mr. McBrue take a little road trip to visit this north Florida expert - if only to test his 140's system prior to the hot weather.
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Josh wrote:

Uh oh:
"Two of its finest lines of the last 20 years, the 124 and 140 chassis, now come with footnotes about their cost of ownership due to air conditioning costs. We will probably do 10-15 of the 12-hour 124 model evaporator replacements this summer, and two or three of the 22-hour 140 chassis evaporator jobs."
I'm beginning to think that it's not such a bad thing my w124 came without AC. I'm thinking of having an aftermarket (manual) Diavia AC unit installed this spring. I was quoted 1700 EUR for that. Anyone have any experience with aftermarket units like this? Sounds like it could be cheaper than an evaporator replacement...
Ximinez
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and an almost fanatical devotion to the Pope....
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