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Old 06-06-2003, 08:56 PM
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Join Date: Mar 2003
Location: Los Angeles, CA
Posts: 445
ACC control module

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?
1972 450SL
1982 300D Turbo
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Old 06-06-2003, 09:05 PM
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wjm wjm is offline
Join Date: Dec 2000
Location: Suburban Detroit, MI
Posts: 692
I don't think I'll be able to answer your question. but I can tell you that I just replaced the A/C Control unit on my 94 E420. Purchased it from a junkyard for $45. Worked great. Nothing was wrong with mine except for sticking buttons... which I could never seem to fix even with electronic cleaner.

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