Sorry, it's not an "a/c" button per se. Again, I'm using the W126 as the baseline, but the button that will engage the a/c is the middle button in the group of five. The defrost button (all the way left) and the bi-level button (second from the left) will also engage the compressor, but, let's just stay with the standard a/c function which is the middle button.

If the W124 does not have five buttons in a row, then ignore the above advice. A W124 member will chime in.

Yes, I can direct you on how to hotwire the Klima, if it is determined that this is the problem. But, this is a relatively complicated task and it's of no value unless we confirm the pushbutton unit is doing the proper job.

Furthermore, the W124 pins are slightly different so I'll need to get the advice of another member (BrierS) for assistance.

Beg, borrow, or steal an ohmmeter or go to Radio Shack and buy a small meter for about $15.00. I have one of these for 20 years and it's great for small jobs when you don't want to drag out the big meter.

This is how it looks like
I took a pic when it was out.
The reason I asked to hotwire the AC bypassing the klima was to find out the ceap way if indeed the klima is the problem. If it works then I'll buy a klima rely, if not I'll get the ACC unit. I found it online rebuilt for about $239

Personally, I'd be looking for the electrical gremlin related to fuse #6 before I was thinking of "hot wire" to the A/C unit. May be related.

I disconnected everything related to fuse no 6. Still the same problem. Also what is crazy is that as soon as connect a fuse at no 6 my aux fan starts and I hear a lot of clicks around the engine, maybe even ac compressor clutch? The auxiliary fan is in no way related to that fuse. it is related to fuse no.7. I started the car and then pluged in a fuse at no 6 nothing happened, but the AC compressor didn't come on, I stoped the car and took the key out, and every single light inside the dash is on,... everything including the glow plug warm indicator, buzzer going and the fan spinning.... crazy?

Again, you have the cart before the horse.

First you must determine if the Klima is getting a proper signal from the pushbutton unit (that's the same unit on the SDL, BTW).

Then, if it is, the Klima might not be the culprit. It might be any of four signals that the Klima receives. The whole purpose of the Klima is to dump the compressor if any of the signals are not within specs. Many people have replaced the Klima and the problem persists because the poor Klima was simply doing its job.

Tell you what:

You go out and get that meter. I'll do the research and figure out which pins to test for you to confirm the problem.

How's that?

Sounds good. I'll do that today

OK, once you get the meter, set it to read ohms and perform the following tests:

Test #1:

1) Pull the Klima from under the hood.
2) Set the temperature wheel to full cold, all the way to the stop.
3) Start the engine
4) Press in the middle button on the pushbutton unit (PBU)
5) Connect one lead of the meter to ground on the battery
6) Connect the second lead of the meter to socket #10 of the Klima relay.

See if there is continuity. Is there a ground signal on socket #10?

Go back inside the vehicle and press the fourth button from the left (the button to the immediate right of the center button).

Return to the Klima sockets.

See if there is a ground signal on socket #10 (repeat the test).


Test #2:

With the engine running, use a test lead and connect sockets #5 and #7.

The compressor should engage. Confirm that it does.


Report back with your results.

Alright Brian, here is the result:
the meter set to OHM reads OL constantly on all OHM settings 20K 200K 2M etc when connected the black to the ground of battery and the red to #10 on the klima socket. I tried with the ACC setting to cold all the way until it clicked and the middle button fan on high, then with the button on the right.
When connected the #5 and #7 the AC clutch did not come on. I looked at #7 and didn't see a metal connector like for instance #5 or #10.
Thanks for your help man and need your advice further more

I need some additional clarification:

The meter, when set to ohms, will either swing all the way over to zero on the far side of the scale, or it won't move at all.

So, with one lead in the #10 socket and the other lead connected to the negative battery terminal, tell me what the meter does.

Please clarify what you mean by "no metal connector". Socket #7 should have a proper metal socket, just like socket #5. If it does not, then you have not identified the socket numbers properly, or, that vehicle is not the same as the W124 where I found the info for the test.

Are we positive that you have found and removed the Klima and are testing the correct sockets? How many pins are on the bottom of the Klima?

Some things are not adding up and we can't go further until they do.

ok Brian, sounds fair
the meter I got is electronic
when I set it to OHMS apears OL on the display.
I'll take a shower and rush to the car. I am sure I pulled the Klima relay. I'll count the pins and get back to you, also with the number on the relay itself
In my car is right above the regular fuses, you have to take about 6 screws out. there are about 6 silver relays on top of it.
I'll get my cam today and take some pics.

BRIAN, man you were right, stupid mechanic, I was messing with the wrong relay.
I found the "real" Klima relay, it is behind the battery it writes something like this "D-KLIMA KIKCKDOWN 12V 001 BLA BLA"
First test car running pin #5 and #7 connected (btw #7 has the same connection as the 5 and 10) AC clutch ENGAGED.
Test number 2 - I got ground signal when middle button pressed and the climate set to MIN
Test number 3 - Button to the right of the middle, pressed no ground signal, nothing really readding OL
Thanks man, let me know what do you think is going on, when you have time to read this
Cheers

Excellent results.

So, we know the pushbutton unit is working properly. The problem is with the Klima itself or with one of the signals to the Klima.

In the morning, I'm going to give you specifics to bypass the Klima.

You will need a small relay. If you have an extra "ice cube" relay, like the one's that are in the fuse box, that will be perfect.

If you don't, you need to pick up a relay that will be good to handle about 5 amps DC.

LMK when you get the relay. I need to know the contact numbers for the coil and the contact numbers for the load.

Brian, Thank you man. I was wondering where can I find a cheaper Klima relay. I will like to have the car as original as possible. I haven't try the Benz dealer, but I'm sure it's overprized like crazy.
If you know about a place let me know....
Also I was sondeing if you would like to help me fix my fuse no. 6 mistery once we fix the AC.
Thanks

The problem with getting another Klima relay is that we have not confirmed that the Klima relay is the problem. There are signals that go to the Klima, and, if one of the signals is bad, then the Klima properly shuts the compressor off. So, if you buy a brand new Klima, the problem might still persist. There are specific tests of the signals to the Klima to confirm or deny whether the Klima is working properly.

What I was attempting to do, for you, is to have you setup a temporary solution, so that you have a/c, until a proper diagnosis is made to determine if the Klima is receiving the correct signals, or whether the Klima is actually NG.

A question: Do you have a single serpentine belt on that vehicle? I tend to think that you don't. One of the primary functions of the Klima is to protect the serpentine belt, however, if you don't have a serpentine belt, then the Klima is probably not performing this function. In this case, it's probably there to shut the compressor down if the engine temp gets too high or when you use kickdown (the pedal is to the floor). Both of these functions are certainly not necessary to properly run the a/c.