acc push button module (3rd version) - PeachParts Mercedes-Benz Forum

erubin · #1 05-31-2003, 07:58 PM

After much time and some parts replacement i have an airtight vacuum system in my 1982 300D turbo. The lock system works fine and the climate control vacuum system is completely air tight. All check valves and vacuum elements (pods) were checked and replaced as necessary. The final problem I have is that the climate control flaps remain in the defrost mode (windshield vent and extreme right and left vent are always open). The pods never change state no matter where the temperature dial is set or the push buttons are set.

All the fuses are good but I did notice something which may be key in narrowing down the problem. When i rotate the temp dial from low temp (AC compressor on) to high temp (heat starts blowing) i don't hear any of the electric controled vacuum valves (located behind the push biuttons) making a clicking sound. I do this with the fan set low so I can better hear the characteristic clicking sound when one of the valve should be energized. Some of the electric valves should change state when the system goes from AC to heat mode in order to activate the cooresponding vacuum pod (e.g. footwell or center vent pods).

I suspect the ACC control module or whatever it is that powers the switch/valves is the culprite. Does anyone know how to test this and how to get to the area that needs testing? I guess a new ACC module is expensive and don't want to start swapping parts without troubleshooting first. What can prevent the valves from functioning? What needs troubleshooting and possibly replacing?

While I'm there I would like to convert my dial from Celsius to Fahrenheit as I'm the only "scientist" in the family. Celsius along with the other SI units never did catch on in the 80's cause Ronald Reagan couldn't understand them.

Thanks

leathermang · #2 05-31-2003, 11:21 PM

I have a hard copy of the MB air conditioning and climate control service manual ... for the 123 chassis....
You would not believe how complicated those diagrams are for those switches you are talking about...
I heartily recommend you try to find one of these books for your car... because there is no way I could even begin to help someone with a 123 chassis based on these books.... it boggles the mind how much STUFF they put behind the dash... and how complicated the test procedures are....

--------------------------------------------------------

Another reason I am the proud owner of a 1980 manual control ac, manual shift, manual windows, no sunroof 240d.

erubin · #3 06-06-2003, 08:55 PM

Does anyone know how to test the ACC pushbutton module? I don't want to gamble $200 on a rebuilt part if its not the problem.

My car is a 1982 300D Turbo (so the ACC is called the 3rd version). My vacuum system is leak free and the heat and A/C respond correctly to the temp dial. Problem is that my vacuum elements are not moving the flaps no matter what mode I'm in with the pushbuttons or temp dial.

Per Leathermang's advise I looked up the climate control information on my MB shop CD. Two problems with this:
1. The electric wiring diagram for the automatic climate control is so poorly scanned that it's impossible to see the wire traces coming off the switchover valves. I suspect the switchover valves are not getting voltage so that the corresponding flaps are not moving. But what controls the 5 switchover valves? I suspect that comes from the pushbutton module but could it be from the electronic control unit or something else?
2. The MB shop manual troubleshooting requires using an "Adapter" switch in order to track down problems with the electronic control unit and the pushbutton module. I really am not excited about tracking down and buying such a specialized testing devise from MB which may no longer be available anyway.

I don't want to start tearing into the electrical/electronic portion of the system with no game plan for testing. Daily drivers don't allow for such a strategy.

Can anyone take a shot at this with a bit of Yankee, Deutsch, etc ingenuity?

lrg · #4 06-06-2003, 09:28 PM

Just thinking out loud here but I'd guess you could remove the CCU and look for the valve control, I believe it's toward the right side. First I'd locate the vacuum lines that run to the center vent pods. Then, if possible, try to energize the valve that operates that pod (be careful here, I'd assume that it's a simple 12 volt, low wattage valve but I can't guarantee that.) If it works then try to check the wiring back to the CCU. There's a decent chance that the wire color is the same at the valve end as at one of the plugs that goes into the CCU. First I'd check for continuity from the CCU plug to the plug at the valves. Next, I'd carefully open the back of the plug at the CCU (with it attached to the CCU of course) and try to check to see if any current is running to the valve when you move the temp up and down. Remember the CCU doesn't always act instantiously so give it a chance to work. I've tested some circuits from the back of a plug and usually throughly tape around all the other contacts so as to avoid an inadvertant short. I'd suggest you do the same just to be safe. This is a primative way to try to check things out but it's a start and who knows, maybe you'll get lucky and stumble on an easy fix. Let us know what happens.

romansek · #5 06-08-2003, 04:30 AM

Check 2-stage vacuum elements which operates flaps for defroster jets. I have the Service Manual and can post or e-mail some diagrams. This model have total (5) vacuum elements for control of air flow.

erubin · #6 06-11-2003, 08:04 PM

Unless I get a more definitive troubleshooting suggestion from someone I will proceed per LRG and dig in with a meter, 12V power supply...and try to trace the problem.

romansek said to check the 2-stage vacuum element. I already replaced it as well as the other faulty elements (per my first post above). Your offer for a diagram is very appreciated. As I mentioned my CD of the manual has a real bad scan of the wiring. The diagram I need is from the Climate Control manual (version III). The document is 83-603 "Function Test of Total System". I only need page 15 which is "Electric Wiring Diagram Automatic Climate Control Model 123.0, 123.1".

romansek: I will e-mail this pdf file from the CD so you can see exactly the diagram I need. You will notice that the wire lines are invisible because MB did such a bad job scanning this page. Hopefully for me you can do a high enough resolution scan from your paper manual so I can see all the traces. Thank you in advance.