[W126 Coupe] RE: MBCOUPES Digest, Vol 22, Issue 19

[Jack]

Hi Dick,

I found that the vacuum lines on the switching vales were leaking. When I
applied 25hg on the center console the element ruptured. Now I get to change
that one! I wish I would have known about the 15hg part! The manual says you
have to remove the console and the center vents to get to it. Waahhh... Do
you know of an easier way?  Fixing the switching valve problems got the air
blowing out the right vents finally.

I'm still sorting out the heat blowing out the vents all the time. I'll try
the functional test as you recommend 

Good thing I'm doing this myself. A shop would have charged me about what
the cars worth to fix this. Next up, a new a/c compressor and replacement of
a leaky fuel return line. 

If this car didn't drive so well, I would have got rid of it a long time
ago. At least we have a well equipped garage, even have a scope and 4-gas
here.

Thanks again!

Jack

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
I would recommend you run the tests in 83-601 to see where the fault(s) lie.
If no air is coming out the center vents it's being diverted to the defrost
vents and/or to the leg area. If you can access the vacuum switch valve to
the right of the center console and have a Mighty Vac
(MV) handy, you can test each of the individual vacuum elements one more
time without having to get at each element directly. Just unplug the
respective vacuum line and run the connected MV up to 15 hg or so and let it
sit for a minute to see if the needle creeps lower. (I wouldn't go much
above 15hg to protect the rubber diaphragms from rupturing) If all the
elements and their respective vacuum lines check out, then one remaining
possibility is that one of the element linkages is stuck or a pivot on say
the leg flaps is broken in the heater box. I found that
83-601 done in an orderly fashion pretty much gave me the details of what
needed fixing.

By the way, I just replaced the complete ACC head last weekend in the 86
300SE with a rebuilt (warranty 2 or 3 years) from Ken at
<www.thebenz-store.com>. This was the sedan that I rebuilt the ac and vac
elements on 2 years ago. Worked fine for 2 years but, started behaving in
such a manner a few weeks back that I once again ran the tests in 83-601 and
determined that the head unit this time round was all done. An important
note found on the new unit instructions says "check that there in no reading
at or close to 0-ohms resistance on both the mono-valve head and the coolant
recirculating pump as an external short on either of these components will
damage and void the warranty on the acc push-button unit". So, as an
additional test you can and should check these two devices with an ohm meter
with electrical disconnected to see if they are working showing and open vs.
a short as the instructions recommend. I tested both my units before
installing the new head unit and found them to be in working order. I took
the added step of running 12VDC across each unit to see/hear the operation
was as it should be... Clicking on the solenoid element for the mono-valve
and the buzz and sounds of coolant being pushed though the heater core on
the recirc. pump.

The behavior I just dealt with was in fact the vacuum switching valve
changing air distribution locations erratically along with the 'Auto' 
button having been selected causing wild shifts in the fan speed. Every time
I'd hit a bump in the road the system would start mis-behaving. 
Again, I diagnosed using 83-601 before laying out $155 to effect the repair.
I didn't bother withthe cold solder joint repair where I had done this 2
years earlier and felt that after 20 years a reman was in order.

Good luck, keep at it.

Dick

Jack wrote:

> Hi again,
>
> Ive got the vacuum elements switched out, no more leaks. But the air 
> wont come out the center vents.
>
> Anything other than max a/c also blows hot air. Not good when its 
> already 100 degrees out here. I changed out the mono valve too.
>
> What the heck is going on with this thing? The center vent (40) 
> element didnt leak but I dont hear any movement when adding vacuum.
>
> Looks like a pain to get in to that one!
>
> Jack
>
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