Hey guys, just bought a 1987 300D Turbo with 250K miles.
RUNS GREAT fast and solid.
3 problem with it
1. fixed no cruise controled, replaced some old vacuum hoses and cruise control works
2. NOT FIXED sunroof doesn't open I hear the cable moving so maybe a cable problem, will look into it later, but here is my real problem:
3. NOT FIX - A/C not working, compressor and clutch good. The car has been recently converted to R134a. The diagnostic is - NO POWER TO AC COMPRESSOR. I have been told that the ACC unit inside the car is not good,
all the buttons work fine, fan, heat etc.
I just open the fuse box this morning myself and saw that the fuse no. 6 is missing - checked what it was for , horn, turn signal and I forgot what else, anyway I tryed to replace the fuse and all my dash board lights went on, as if you try to start the car, including the buzzer box. the horn and turn signals work fine though with out that fuse, but they work all the time, even when no key in ignition.
The auxiliary fan comes as soon as you try to start the car and never shuts of unless you turn the car off. One mechanic told me that it is a short somewhere that's why the fuse 6 is always hot.
Thanks guys and please ask me any additional questions. I'm on my way to the benz dealer to buy a new ACC unit, I live in Sacramento California and the temp is about 103F today

Who diagnosed it and how did they come to this conclusion?

A mechanic at Imorts specialists shop in Sacramento

OK, then.

Hopefully he nails it. But, it's a complicated system with all kinds of sensors that can prevent a compressor engagement.

I recently spent an entire weekend chasing a similar situation.

You purchasing a brand new pushbutton unit?? That's got to hurt.

The dealer doesn\t have the ACC unit in stock, anyway I was about to walk away from the $696 bill anyway
I took the ACC unit apart, looking for unsoldered wires, connectors, items etc

Have you considered a rebuilt ACC unit? The cost is more like $275 plus a core deposit, and they are fairly simple to install. Most of them have some kind of warranty.

Yes, That's what I will do, but I would really want to know for sure that is the problem. I have read here a lot about defective ACC units, from fan blower problems to not blowing any kind of air at all. Mine works fine, everything on it, except when I turn it to cold max AC compressor doesn't engage. I say again AC compressor works fine when tested. Also the same mechanic replaced the AC relay controller with another one and still no power, then he diagnosed the ACC unit to be faulty. Also how come the aux fan is always on and the fuse no. 6 is crazy? Any idea? Thanks a lot I really apreciate all this help.

If he replaced the AC relay controller (Klima), the question I would raise is whether he confirmed that the Klima is not receiving the ground signal from the pushbutton unit. If the Klima fails to get proper speed signals from the compressor, and the engine, it will default, deliberately, and cut power to the compressor. In this case, replacing the pushbutton unit won't accomplish anything.

I already have my doubts about the capability of the mechanic if he simply replaced the Klima and it did not solve the problem. He could have easily confirmed whether the pushbutton unit is sending the ground signal to the Klima. Only if there is no ground signal would the pushbutton unit be suspect.

I can't take the ACC main board out without breaking the buttons. LoL
I messed up one already but managed to fix it. is there a misterious way to get inside the box?
also I forgot to mention that the GERMAN,... EUROPEAN really, plastic are REAL GARBAGE! they break as soon as you barely touch them

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I never intended for you to go inside that unit. That's a hopeless proposition. I don't think you can be successful in attempting to repair it without very specialized equipment and a thorough knowledge of its relay logic.

My curiosity was simply whether the unit was providing a ground signal to the Klima, or not.

Brian, I know you are right, just closed the unit. How do I check if it sends a ground signal to the Klima?

I agree, this does not sound like the "usual" failure mode of the ACC unit. I would hate to see you buy a new (or rebuilt) unit if it's not the problem. The folks that sold me a W123 rebuilt unit (General Development Laboratories) told me they could test my old unit before they sold me a new one, but I don't think they sell W124 units (http://gdl-online.com/begin.html). Maybe you can find a ACC rebuilder that will check yours?

You install the unit back in the vehicle.

Go under the hood and remove the Klima. It just unplugs.

Set the temperature control to full cold, all the way to the stop.

Start the engine.

Press the a/c button.

You need an ohmmeter. You are looking for a ground on one of the sockets that the Klima plugs into.

On the SDL it is socket #10. However, I can't confirm that the W124 is identical. If someone has the W124 schematics, hopefully they can confirm this.

If you have a ground signal at this socket, then the pushbutton unit is not the problem.

Brian, Thanks, got it
The unit is installed back in the car, everything as it was.
The only problem is that I don't have an ohmmeter anymore since I gave it to a friend that never returned it back.
I was wondering if there is some way to bypass the KLIMA and somehow "HOT WIRE" the AC unit, like a direct connection in the Klima socket

Oh Brian I forgot I don't have an AC button, you mean just turn it all the way down to "MIN" cold? Right?