I had two of those old units but they were beyond repair so I looked into different options - in the end I bought the unit from unwired tools. It took about 1/2 day to put it in. It never failed since I installed it in May 2011.


https://www.unwiredtools.com/

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'80 300 SD, 300k

Whoa. I think you are getting a little hasty with your judgements of ACCII and the UT unit.

If you want to spend your time and money tracking down hard to find and definitely unreliable components to fix up your ACCII, more power to you. I can understand if you want to keep that originality vibe and that's cool.

For the rest of us who want something that works the UT kit is a perfectly viable option. I installed one myself in mine and its been solid as a rock for 6 years now.

@cooljjay fresh air control can be achieved very very simply with the addition of one manual controlled vacuum valve to the fresh air flap.

If you go making assumptions like that couldn't be the problem because those never fail unless you hit them with a hammer then i think you're going to have a tough time getting it sorted out.

Push button units do fail after years of people pushing in the buttons to hard until it shorts out and melts down the electrical connections.

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Current fleet
2006 E320 CDI
1992 300D - 5speed manual swapped

former members
1984 300D "Blues Mobile"

1978 300CD "El Toro"

I am going by my own experience as well as the experience of friends, including one who has been working on these cars since they were brand new on a daily basis.

I would disagree that the servo is an unreliable part. It fails eventually, yes, as most components do. I own a 1980 450SL that was purchased new by my father in 1979. The original servo unit failed, (started leaking), in the early 2000s and was replaced by another factory unit. It is working flawlessly to this day. THat means that the OG one lasted approx. 25 years in Minnesota with brutal extremes in temperature between winter and summer, it was probably used almost every time the car was driven for either heating or A/C.

The replacement part is going on 10 years with no sign of failing. It helps a lot to keep clean, correct coolant in the system. Once again, many supposed failures on cars can be traced to improper or cheapskate maintenance/lack of same. Not all, but many.

I've lost count of how many of these cars I've owned and mechanically restored, returning each one to as close to factory performance as possible. The person whose experience and opinion I trust even more is a friend who has owned a top independent MB repair shop since 1982. Prior to that, he was a dealer tech and shop foreman at one of the largest MB dealers in Los Angeles. He has worked on thousands of w116s/r107s/w123s/etc. from the time they were brand new and he was doing PDIs on them to the present day when many are horrible POS cars. He is also in the position of trying to help customers who may be short on funds and are trying to keep an old w123 or other Benz on the road.

The climate servo unit is obviously an expensive part, until MB recently dropped the price it could be more than the value of some of these old cars. Years ago when I put the new one in the SL, they retailed for around $1200 but were available from aftermarket suppliers for around $500. Then MB jacked the price to ~$1700 and the supply of OEM replacements dried up. Good used ones have always been gold.

Now MB has unexplainably dropped the price of both servos with the w123 part retailing for ~$500, (06 part#), and the 107/116 unit, (03 part#), about $1200 list. This is why I wanted to know the difference, if any. My pal with the shop could not remember what if any difference there was in spec between the two. He told me to check on an internet forum and see if someone knew.

When he says that the push button unit almost never fails, I listen. We're talking 40 solid years of experience including recalls, warranty work, factory training, working on them when they're old and neglected, etc. When he says that the aluminum replacement units are inferior junk and he won't install them, I listen. And I don't even have to ask him about the electronic hack part, it looks like someone on a desert island with nothing but a rusty fork and some old radios tried to fix the system. It is garbage. The original system was quite an engineering feat for its time, designed of course by Chrysler not Mercedes-Benz. They work well if maintained.

Just a few comments from a historical perspective (I joined my first Mercedes discussion list in 1995 and purchased my first diesel, a w116 300sd, in 1997).

Agree: the servos can last if and only if the OE-spec coolant is used. The one in my SD was 9 years old and working fine when I sold the car. I bought my coolant at the dealer.

Footnote on coolant: Bear in mind, however, that Zerex is a relatively new development, and prior to that you had to fork over dealer prices to get the correct spec coolant. Not everyone was happy with that. Even indy shops were known to give customers a choice of whether they wanted the expensive stuff or plain prestone. Prestone, especially if left sitting with the car not used for any period, killed servos.

Agree: the ACC II was a great achievement for its time, given it was likely developed in the early 1970s. I argued this recently in another thread, to much muted snickering and elbow poking among the gathered faithful.

Disagree: that the metal bodied servos were always inferior. George Murphy did not simply invent a market for upgraded servos.

My experience with my SD notwithstanding, there were a lot of the ACC II-equipped cars still on the roads back when I had mine and many, many people saw servo failures of the OE units within 3-4 years. It was a common topic of discussion (lots of people joined the list for that reason).

At that time the OE was ~ $1200 and really only reliably available from the dealer (sometimes guys like the Rusty Cullens/Jabba Hurst show could get them for less, sub-grand).

George Murphy supplied a real niche back in the day. There were complaints from time to time about his version, and in fact he admitted once or twice his producer had fallen off the QC wagon and at times he stopped selling the metal-bodied ones until he found a new supplier.

I don't know what is up now, maybe things are different. (I am not a George Murphy fan by any means, but I will criticize him for what he'd due for it for, not for this.)

Point out: a significant reason that ACC II continues to be the subject of scorn is largely that no one -- and this blows my mind -- in all this time, all these years, has ever done a front-to-back end simplified plain-language DIY for the system. I really don't get it. There are nicely illustrated, well-written articles on all manner of difficult jobs (even converting the system over to ACC I, wow), but only piecemeal stuff for ACC II.

People generally distrust what they don't understand.

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

Perhaps it was installed incorrectly? Two other people in this thread just said theirs works great and they both installed it themselves.

My ball valve "hack" works flawlessly...dare I say guaranteed to work versus 3 leaking servos and $10 is quite a bit less than $500 or $1200 or how ever expensive you say new servos are.

How do you know that all she needed was just a servo from simply looking at receipts? Perhaps the old lady did indeed take a hammer to the push button unit twice? The point is you are making a lot of assumptions here.
Funny. I bought three used servos and they all leaked shortly. My ball valve from Lowe's is holding up just fine. You are more than welcome to pay the bill for parts for my car if it really bothers you!

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2009 ML320 Bluetec
1985 300CD
1981 300TD

Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD

I agree about the servo lasting 40 years and of course it will need to be replaced....a good majority of people on this forum, believe that nothing and I mean nothing is suppose to wear out and need replacing on these cars. Just mention to people that they should replace their starter, because of the age....and you start a huge debate....bigger then the debate on if there is a God.....

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If you replaced your servo with a toilet valve from the hardware store and your ACC works fine now, your skilz are impressive.