W140 A/C Push Button Control

I have a 1996 S420 with a MB # 210 830 04 85 (now 140 830 24 85) A/C Push Button Controller. The EC button is broken in the on position...I don't think the A/C compressor is running as a result.
Does anyone know the diagnogistic codes and procedure to get to the diagnostic mode? MB wants $866.00 for a new one, and I cannot find one used.
This is a great car, but with no manual to troubleshoot, MB service...as good as they are...has me by the short hairs.
Thank you to all who respond.

I have checked the codes by pressing the rest button...on number 9, the readout is E. I've read somewhere in the threads that #9 represents software status. What does the E mean?

[JimF]

my S500 page?

Click "www house" below, select menu #15.

I have to say, your website is one of the most informative I've seen!!! It's fantastic.
I did discover yesterday that by pressing the rest button, I can read the operational check of the A/C System. I do have what I think is an error...Under test step No. 9, I get an E. I assume that it means that something in the Pushbutton is bad and that nothing else is affected...however, I have not read out the DTC's yet. My A/C Pushbutton is newer than the one you have shown...I'm still trying to figure out how to get to the DTC codes.
Any information on this would be much appreciated.
Thank you

[JimF]

are for W140 chassis up to 8/95. For your car, the 'values' are different and have been expanded.

A "9" for my car ('94 ) is software status but for your car, there is no "9", so maybe that's why you get a "E".

A gentleman from Continental Imports was kind enough to send me in the right direction. I am told that the EC light usually means that the system is low on freon. I'll have to take it in for a check. I cannot figure out how to access or delete the DTC's...I'd like to give that a shot first. Hopefully someone can give me some insight before I give up and take it in.
Hope the problem is not too expensive.
Thank you for your assistance.

[JimF]

then I would agree that you can't acess the codes and start the compressor. You can verify that pretty easily, just look and see of the clutch is engaged. If not, the EC button must be fixed FIRST.

Under number "7", the refrigerant pressure, in BAR, can be seen; 13'1 = 13.1 bar (191.1 lbs). This is nornal pressure for a 'avearge' day, temp, etc.

Unfortunately, Number 7 shows a value of 34??? I do not think its representing the pressure. Number 24 however shows a value of 14.1...perhaps that's the pressure we're looking for. I've done some exhaustive research and cannot find much on this subject. You have been most helpful.
Thanks,
Charlie

1996 W140 S420 Sensor Values...
1 In vehicle Temp Sensor w/ Aspirator Fan
2 Outside Temp Sensor
3 (1) left Heater Core Temp Sensor
4 Right Heater Core Temp Sensor
5 Evaporator Temp Sensor
6 (1) Coolant Temp Sensor (Climate Control)
7 Coolant Pressure (06 = 6 Bar)
8 refrigerant temp Sensor
10 Blower Control Voltage
11 Emissions Sensor Voltage
12 Sun Sensor Voltage
20 Current for Aux Fan in Milliamps
21 Engine Speed in RPM
22 Vehicle Speed K/Hr
23 (2) Battery Voltage at Terminal 58D in Percent
24 Battery voltage
30 Left Heater Core Temp. Sensor
31 Right Heater Core Temp Sensor
32 Rear Evaporator Temp Sensor
33 Rear Blower Voltage
34 Left Rear Temp Sensor
35 Right Rear Temp Sensor
38 - 43 Hardware and Software Status

(1) - Display will show 2 digits, for example...104 F will be 04 F
(2) - Voltage is displayed in percentage, for example: 99.0 will be 99% Battery voltage

I have the DTCs also if anyone is interested.

[h_shek]

very imformative I must say.

Can I ask how any of these checks can be done if some of the buttons aren't working? (or should I say works after pressing 50 times in different angles)

I have that problem and my AUTO, REST and Recycle Internal Air buttons are all like that!!!!

I suspect its a bad button sensor. Any advise?? If I can't get AUTO and REST, I can't do any of the checks mentioned.

Any help appreciated and well done on the web!!

Cheers

I've spent some time on this and have learned a lot...In your case, the little tabs on the other side (the working end) of the Push button(s) are probably broken. I took mine apart a few days ago and discovered this condition. You would be amazed as to how intricate and flimsy the assembly is. So with a little ingenuity and some glue, I managed to get them working again. However, the EC light remained on so my problem runs deeper than that...
I took it to my mechanic who informed me that yes...a constant EC light means the system is low on refrigerant (1996 S class on up)...and sure enough, he had to charge the system and add a dye pack to find the leak. It will take a few weeks to bleed enough to trace.
My climate controller, however, seems to be missing some brain cells...it still thinks the system needs refrigerant even though it has been charged...the light sporatically comes on. It too probably needs to be replaced.
MB wants $866.70 for a new one...pretty stiff, my mechanic says he can get a rebuit one for approx $500.00 and in the meantime, I'm looking for a used one. Not much luck at this time.

[JimF]

for keeping us posted.

Didn't know about the EC light for '96 and later. You are a man after my heart: there's nothing that a little ingenuity (and some glue) can't fix! Good stuff.

On the bottom of my main page, there's info for networks that specialize in getting Mercedes parts: used, OEM, second source. It has worked for me in the past.

[h_shek]

you got to be kidding me. You took the wood panel out, took the A/C control unit out, remove the buttons from the unit, apply glue on the thing, put the buttons back onto the unit and finally put the unit back to the car. All that??? Are you serious!!!

If so, I would like to know the following:

1) what tools you used to take the becker radio out? The radio removal key? or are there something else we can use?

2) What tools u used to remove the A/C unit? Screw driver or special tools?

3) What tools you used to remove the buttons from the unit? Is it screwed on? or glue on? or clip on?

4) You mention "glue" something behind the buttons? Is it dangerous? Is it easy? Will I damage something?

5) I assume everything can go back easily, right?

6) Can you unplug the unit from the car for a long time, like 1-2 days? Will it resets itself with no power connected? Did you remove yours or you just did all that while connected?

7) Buying a new unit, again can a new unit just plug-n-play? or we need MB to program it to work on the car?

8) Is your control unit the same as the one shown on "JimF" page? You know, seperated into 3 segments with 1 wheel on each segment? or you have the later model with one long LCD panel?

Mine is a 92 W140, hope what you said will really give it a kick. I really need some of those buttons.

Thanks a million for your reply and help.

Good luck in sourcing the unit, but my advice is a brand new unit. Mine had the same button problem in 98, had it replaced by MB, and gone again in 2001. Lucky the "0" button works.

Lots of questions...but you have the older model W140...mine (being a 1996) removes easily with the radio removal keys...it takes just a few seconds. After removing the unit, there's three screws to remove and some pieces snapped together. From there, the back side of the buttons are exposed with all the broken parts. I glued the tabs back on, then reinforced them with some old cut up credit card plastic...doesn't sount pretty, but it worked to get the buttons operational. It didn't help the software problem however...as you can see from my earlier posting.
Jim F...If I had only known about this site a few years ago, I would've saved a ton of money. MB likes to keep the W140 a big secret. I'll check your sources.
Thanks Again...
CK