Weak blower even after regulator replacement - Page 2 - Mercedes-Benz Forum
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post #11 of 16 (permalink) Old 05-08-2019, 08:47 AM Thread Starter
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OK, I did some investigation just now and it seems that the evaporator temperature sensor always shows a too high temperature. I put the AC in LO and when the in-car temperature sensor showed 18C and the heat exchanger sensor showed 15C, the evaporator sensor showed 27C which probably cannot be true. I also pulled both the heat exchanger and the evaporator sensors and measured their resistance. I waited a bit until they were certainly at ambient temperature, and the former had a plausible resistance reading while the latter indicated around 10C more than it should have.

As far as my winter experiences go, maybe the problem was that the compressor actually was running even though it was freezing outside, because according to the evaporator temp sensor it never got cold enough to disengage the compressor.

Anyway, this looks extremely promising. I'll have to figure out where I can find a replacement sensor quickly. Thanks everyone, especially @Ears !
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post #12 of 16 (permalink) Old 05-12-2019, 01:51 AM Thread Starter
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I got and installed the new evaporator temp sensor on Friday and yesterday I was able to test it when the Finnish MB club had an R129 30th anniversary drive and gettogether. The problem is gone!
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post #13 of 16 (permalink) Old 05-12-2019, 05:59 AM
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I got and installed the new evaporator temp sensor on Friday and yesterday I was able to test it when the Finnish MB club had an R129 30th anniversary drive and gettogether. The problem is gone!
Boogity! I believe this issue is more common than reported, as it is not easily recognized. When this system is working as designed, it is a thing of beauty. When I overhauled the ACCIII in my old 107, I was greeted with the same realization. The R129 is no less "magical".

Glad you got it sorted out...

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Where is it again that we are going... And why are we in a handbasket?
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post #14 of 16 (permalink) Old 05-12-2019, 12:40 PM
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I know where the evaporator temp sensor (2108300772) is in the driver's footwell, but where is the heater plenum temp sensor?
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post #15 of 16 (permalink) Old 05-12-2019, 03:18 PM
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I know where the evaporator temp sensor (2108300772) is in the driver's footwell, but where is the heater plenum temp sensor?
Directly behind and a little left of the climate control panel and radio. You can change it thru the opening without removing anything else. Easy-Peasy...! When I changed evap sensor, it made a big difference... When I changed the plenum sensor, it corrected all issues, and the system worked better than I expected.

I'll look and see if I have a picture. 126 830 17 72
https://www.benzworld.org/forums/r12...l#post17484471 Sorry, No Picture.
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File Type: pdf Heater core temp sensor location.pdf (29.6 KB, 10 views)

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Where is it again that we are going... And why are we in a handbasket?

Last edited by Ears; 05-12-2019 at 03:42 PM.
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post #16 of 16 (permalink) Old 05-12-2019, 09:24 PM Thread Starter
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I know where the evaporator temp sensor (2108300772) is in the driver's footwell, but where is the heater plenum temp sensor?
The heater core sensor is in the wall right behind the AC control unit. The part number is A1268301772. Mine is OK so I didn't replace it. I might have, but there seems to be little to no aftermarket availability, OEM seems to be the only way to go, and I couldn't get one quickly. Maybe the fact that it's a 126 number means the original design is still fine and they don't fail often.

Edit: Oops, didn't notice Ears posted already. Oh well.

Last edited by juuso; 05-12-2019 at 09:53 PM.
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