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  #1  
Old 04-27-2011, 01:14 AM
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Location: Phoenix, AZ
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Engine won't shut off when climate control off -- otherwise ok.

Strange problem: whenever my climate control pushbuttons are set to AUTO LO or AUTO HI, the car shuts off perfectly, nice and quickly. But, when the OFF pushbutton is pressed, turning off the fan, then the car takes a few seconds to shut off -- as if there's not enough vacuum getting to the engine shutoff.

My climate control works great, and the rest of the vacuum in the car works well too -- doors lock & unlock, but sometimes they lose vacuum when I haven't been to the car for a while and won't unlock when I unlock the driver's door.

I feel like there's a leak in the pushbutton controls when I am in the OFF mode. I don't know what to check for, though, since I haven't been able to find a diagram of the pushbutton unit itself. I made a colorized version of the vacuum diagram that might help someone sometime, but I can't seem to figure out what happens to the pushbutton switch in OFF mode:



Any ideas?

Thanks!

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  #2  
Old 04-27-2011, 02:23 AM
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Location: central Texas
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I believe you are correct in your assumptions.
The MB AC FSM has the diagnostics for that type of stuff... but for the things in the dash it is 80 pages long....
Is the ' power servo ' that big thing .. perhaps in a fiberglass shell in the engine compartment ? Usually associated with the word ' nightmare ' ?
The FSM gives the max allowable leak rate for some of that stuff... but I have not found any diagram like the one you show... which is nicely done since the FSM just has black and white and is not labeled except by numbers... a real pain to look back and forth to try to identify anything...
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Old 04-27-2011, 02:32 AM
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The servo is indeed that big black (or aluminum, depending) thing near the firewall on the right side (just behind the air cooler). It's a nightmare! But, I did succeed in rebuilding mine using some parts from another one or two defective ones someone gave me. It works great now! Ask me if you have any questions about how this works.

My problem has to be a leak, related somehow to the "off" position of the pushbuttons. What I want to figure out is what the vacuum slow is when the switch is off. Is it just a closed valve that might be leaking? Or does it lead to another vacuum line that should be blocked but isn't? Or does it lead to a leaky diaphragm that should be closing but is leaking? If you do have the FSM or diagram for that, it'd be great...thanks
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  #4  
Old 04-27-2011, 02:41 AM
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I can not find one that looks anything like your diagram.
but can relate this general blurb at the front of the testing section.

" The vacuum system is subdivided into 7 text circuits, the main switch, the compressor switch and the switchover valves. If a given trouble prevails eg, center jet not opening, the respective circuit can be tested first.
If a leak or functional trouble is suspected in entire vacuum unit,proceed according to 83-615 and preform each time the first test step ( total test ) of an individual vacuum circuit until the faulty vacuum circuit is found. Then continue testing the respective circuit until the fault is found ."

Two special tools are specified
116 589 25 21 00 tester for vacuum
115 805 03 22 distributor

self made plugs welding wire 3.. dia 40 mm long
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  #6  
Old 04-27-2011, 02:45 AM
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Hi Leathermang...I just came across this:

http://handbook.w116.org/Climate/83-621.pdf (testing pushbutton switch). I'll try that tomorrow. Still no diagram, but maybe that will show me that it is not working right.
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  #7  
Old 04-27-2011, 02:48 AM
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LOL, ' Blind ' plugs... if something is plugged it is plugged.... no adjective is needed....
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  #9  
Old 04-27-2011, 02:57 AM
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Location: central Texas
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That page starts off..
testing check valve
pull connection from check valve 32
connect vacuum line of tester evacuate and read gauge
if gauge shows presure increase , replace check valve

next is testing vacuum reservoir
bottom line... replace gasket of vacuum res 33

then it goes to temperature switch... they are using special tester mentioned earlier...

you could start by replacing those items .... ???

it looks like there are only two check valves and they are both inside the car...
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  #10  
Old 04-27-2011, 10:58 AM
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I would begin by plugging the green line that feeds the whole climate control system and confirm that the car shuts off fine with the climate control system completely out of the loop. If it does, I'd then move on to the various components of the ACC system, plugging lines to see if it solves the problem.
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  #11  
Old 04-27-2011, 04:01 PM
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It does. I tried that this morning. I also removed the pushbutton controls and checked found the check valve (#82 on http://handbook.w116.org/Climate/83-604.pdf), thinking it might be the culprit (if I block the black line from the pushbutton right there, the engine shuts off). I realized (after reversing it, since it worked fine), that it needs to be there to enable the center vents (I guess prevent it from going into bi-level). So, that wasn't it.

I have a spare pushbutton set and tried connecting it, and that didn't help, either.

Next, I will try to find check valve 81 (anyone know where it is?) and see if it's defective.
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  #12  
Old 04-28-2011, 12:56 AM
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the system in your car is a little wonky compared to the later ones. i remember coming across the specified leak point with factory wire jammed in it...im sure my 123 is different but the vaccum switchover valves were leaking when activated. it was screwing with my trans. i just got 5 new ones$$$
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  #13  
Old 04-28-2011, 08:43 PM
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Quote:
Originally Posted by r.e.wing_fc3s View Post
the system in your car is a little wonky compared to the later ones. i remember coming across the specified leak point with factory wire jammed in it...im sure my 123 is different but the vaccum switchover valves were leaking when activated. it was screwing with my trans. i just got 5 new ones$$$
I think I have one of those behind my glove box You think that was plugged from the factory?
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  #14  
Old 05-13-2011, 11:33 PM
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Vacuum leak - pumping brakes keeps motor running

Jumping in here to keep the 1980SD 116 thread alive.... I have had a slightly longer shutoff sometimes but not other times and have not mailed it down yet. The other night while turning off the key i starting pumping the brakes 4 or 5 times (to see what would happen given it's part of the vac system) which kept the engine going for an additional 20 - 30 seconds. Have not had the time to investigate further but now more concerned.

Anyone else experience a similar issue? Today the client control would not shutoff until i rotated the temp dial until it was at max cool (AC not working, but that's another thread), pushing the OFF button had no effect. Previously there was a delay in pushing the OFF button and the system turning off, probably 3 - 6 seconds.

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Last edited by ckamila; 05-14-2011 at 12:32 PM.
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