I have started the ball rolling to come up with a "conversion" kit for the automatic climate control system on the W123/126 models. I have my electrical engineer friend from work involved and I hope we can come up with an inexpensive PLC/manual switch control system that can be installed in the 123/126 models to replace the screwy automatic system. My way of thinking is that we will have a three position switch for the fan and a rheostat to operate the monovalve. Switches will be used to operate the solenoids that operate the damper actuators. I'm going to let my electrical engineer friend figure out the best thing to do with the monovalve. This should be interesting. The subject test vehicle "mule?" is the 300D which, by the way, runs like a scalded dog now with the replacement engine/tranny and the wastegate spring "cranked" down. I will try to document everything and take pictures as applicable. Any comments/suggestions will be appreciated.

Oh yea - the defrost WILL NOT come on blasting HOT, HOT air when the defrost function is selected - this ain't what we need in south Ga.

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Jim

Look forward to the results of this!

....funny you mention the defrost function and HOT air....I just used the defrost for the first time the other night and thought the system was malfunctioning. Every other car I've ever had turns the A/C on when the defrost option is selected.

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Chris
1985 300SD - 'Grace' (198K mi.)
2018 Honda Civic Sport
2018 Honda CRV LX
2010 Honda Fit Sport (RIP)
2013 Honda Accord Sport (Sold)
1996 Lexus LS400 (Retired)
1995 Ford Contour SE (Retired)
1976 Porsche 914 (Sold)
1972 Datsun 240Z (RIP)

Jim:

You're my hero on this one. What a mess I have with leaky actuators which in turn screw up all my door locks, etc.
One of my daughter's cars ('83) has to have 17 things in the right place in order to turn off (all due to the stinkin ACC deal).

Let me know

Don

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DAILY DRIVERS:
'84 300DT 298k (Aubrey's)
'99.5 Jetta TDI IV 251k (Julie's)
'97 Jetta TDI 127k (Amber's)
'97 Jetta TDI 186k (Matt's)
'96 Passat TDI 237k (Don's
'84 300D 211k Mint (Arne- Undergoing Greasecar Conversion)

SOLD:
'82 240D 229k (Matt's - Converted-300DT w/ 4 speed

In the case of the 123 chassis wouldn't it be simpler to just retrofit a manual system from a 240? Sounds cool though, if mine STB I'll be interested. RT

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When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

I second the motion that the automatic climate control is far too much a pain in the butt to cost what it does.

I wuld be quite happy with the same features for an AC that my humble 89 Hyundai Excel has, together with its trouble-free operation.

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Semibodacious Transmogrifications a Specialty

1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)

"Time flies like and arrow, yet fruit flies like a banana"
---Marx (Groucho)

So the defrost is actually supposed to work like that? I always thought mine was messed up. Hope you get something figured out that will work, I'll buy one when you get the bugs worked out.

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1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k

eng.
Let me know if you need any boneyard parts. A nearby wrecking yard has several 123s, including some with the manual controls. I'd be happy to pull whatever you think you might need and contribute it to this project.

Regards,
R Leo

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Never a dull moment at Berry Hill Farm.

I had thought the big troubles were with the 1980 and before ACC servo. What model years have problems? Asking because I was going to replace my center consol with a latter year (along with all the guts), no sence in doing that if they all have troubles.

Thanks
Don

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1980 300TD-T (82 Turbo and Trans) 159,000 Miles "Jackie-O"
1983 300SD 272,000 Miles "Aristotle"
1987 Jeep Wagoneer Limited - keeps the MB's off the ice and out of the snow
1994 BMW 530it

The 80 and earlier are a whole different can of worms that someone else will have to experiment with.

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Jim

V-Dude, I am available for that project... I have a 1980 240d with the prior system.... and I am going to run to that junk yard before my ( so called ) friend in Austin snaps them up.... lets adopt the goal of KISS so your residual knowledge will be enough to get us through the project....

V-Dude, you remember how cars used to have a cable to pull the choke on... and when the car warms up you push it off ? If you need hot water I am thinking cable to valve....
We may not be on the same page....

V-Dude, First you need a shorter name.... LOL
Second... What do you consider the problems with the original system ? Lets start there...

Actually, I kind of like the ACC when it's working properly. My only gripe is the fan switches - low, auto, and high. Most of the time I want low or medium speed, but there is no "medium" speed button! I hate that. I could live without the "auto", maybe just convert that to a "mid" speed? Hmmm.

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Dave
Boise, ID
Check out my website photos, documents, and movies!

Virgina Dude, I think I see your problem. You have a car with the old, hideous ACC system. The early 80's and later cars (80/81 and newer, I think) have MUCH better systems. Might be easier to just trade up from the '79 to a nice 126 chassis, 300SD or something. And all the plastic tubing behind the dash does last a LONG time - doesn't get brittle. The tubing under the hood does, however. It is dirt cheap - a buck or two per METER of new stuff. I replaced all my vacuum & pressure tubing and rubber fittings on both my 124's for about $25 each - BIG improvement! A lot of that stuff was shot (snapped like twigs). But under the dash, that doesn't happen. Anyway the later systems are really not bad...

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Dave
Boise, ID
Check out my website photos, documents, and movies!

I Agree totally, my Buick Roadmaster has a similar control system and it doesn't work well on auto either.
My "84 300D climate control works OK except AC is always operational on low fan speed, at all button positons, even when off is selected!
I am not very adept at diagnosing these types of problems without an electric diagram.
My AC at one time would not activate the compressor. It did activate however when I would short contacts on the relay terminals. I opened the climate control box and discovered a separated copper trace along one side. This tiny electronic repair enabled the compressor to kick in when it was re-sodered.
The climate controls, cruise control and high revs on highway are the big negatives of these otherwise great automobiles.
Manual control is a dream...
-Tom

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'96 C220 138,000mi, '95 E300D 239,000 mi., '87 300TD 214,000mi '88 6.2 Turbo Diesel Chevy Conversion Van 253,000 mi.