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Center Vent Pushbuttons

2K views 11 replies 6 participants last post by  LWB250 
#1 ·
I'm still befuddled over this:

1994 S420

AC works great, all door/flap diagnostics pass the tests, but the buttons on the center vent have no effect on operation under any mode, nor do the LEDs light up.

I'm wondering if they're disconnected?

I'm going to pull the eyeglasses case this weekend and have a look. Other than that, I'm at a loss to understand why they're completely nonfunctional. As I mentioned, I've run the all of the climate control diagnostics and everything works perfectly.

Dan :confused:
 
#9 · (Edited)
I don't know anything about the reprogramming on the push button control unit but one think I know is that sometimes these units go faulty , on my ex S500 I had to push the button many times for it to light up & function .
It could be that the small push in mechanism behind that red/blue button is just to far pushed in and doesn't make contact when you press on it , just like a tv remote control .
Would be good to swap the unit over from that of a friend to confirm it is the unit itself .
When Ihan had his cluster problem here ,it drove him nuts to figure out the fault , I took my cluster out and tested it on his car ,it confirmed he needed a new cluster as mine worked perfectly on his car .
I'm sure you can find one cheaper then this >>> 92 1992 93 1993 Mercedes 500 SEL Center Dash AIR Heat A C Vent Vents W140 | eBay <<< .
If you would be here in Sydney ,I'd take mine out in a heart beat to test on yours so you would know for sure it is that .
Don't you have a W140 friend handy close by ?.:thumbsup:

BTW: I don't think the early once need any programming ,they are Analog not like the later Digital versions .
Plug & Play ,yours out -new one in & start it up no messing around with reprogramming ,you gotta love the early 140's for that .
 
#10 ·
Unfortunately, I sold the center vent and switches from my former S500.

However, when I have a chance I'll pull the eyeglasses case and check things out. It's remotely possible the the harness for the switches is unplugged.

I know the pushbutton unit is working 100% and has no faults, so all is well there.

I do have a spare instrument cluster I could swap, but I'm not convinced there's a relationship with the cluster like there is in later models. I'll dig into the wiring diagrams and see if I can find anything that might indicate they are talking to each other.

Thanks for the offer!

Dan
 
#11 ·
my 98 center vents looks like the above link posted and I had a problem as well with trying to arrange my vents in working order with the whole a/c. I couldnt get some to blow while others would be blasting, then I'd hit the HI button and side vents would crank but I noticed I couldnt turn the fan speed up... only down. I tried every other button and it seemed to be working so I just pryed out the button itself and *voila, a small short must have heated up and melted the plastic flaired bracket that engages the round button inside. the flaired bracket on the button itself was too flimsy, it needs the plastic to be more riggid to engage the round button on the cumpter face. It was that simple. Hopefully yours will be as well. I didnt even have to remove the a/c cluster panel to fix it. your problem is the center vents, so maybe it just needs some button adjusting or lead cleaning to get a good electrical connection, assuming that everything is working like you say it is.
 
#12 ·
The issue you're talking about involves the later ACC unit, and is a common problem with it.

Mine is for the early unit with the pushbuttons, which has been pointed out several times in the thread.

Let's keep it on topic, folks. Otherwise it's just a bunch of noise.

Thanks,

Dan
 
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