[W126 Coupe] Climate Control Air Flow Issues

[Dick Spellman]

Rick and Rick:

The vacuum pods in the 85 are very accessible but, the 89 if it has a 
passenger air bag is far more difficult in reaching the 2 pods on the 
recirc/fresh air door and the center vent/defrost flap.

In either case you have a vacuum switchover valve on the passenger side 
of the center console.  This is where you can test each of the vacuum 
pods using a MightyVac.  Simply disconnect each line, attach to the 
MightyVac and pull10-15 inches of vacuum.  If the vac holds, the element 
is good. If the vac fails instantly or over a few seconds the respective 
pod up under the dash must be removed and replaced with a new one or 
rebuilt.

The pods are as follows:
2 pods in tandem control the fresh air/ recirculation door.  These are 
up behind the passenger glove box or passenger air bag.
1 pod is up next to the vacuum switchover valve and is accessible when 
the side carpet and climate control are removed.  It's far more 
difficult to access once again if you have a passenger air bag due to 
the metal frame MB added.  This pod controls the defrost/center vent air 
flow.
1 pod is on the face of the heater box.  It is pretty much dead center 
behind the climate control wood console face.  This controls the 
driver's and passenger's foot well heater box doors for air flow at your 
feet. 1 pod drives a linkage that  drives both doors at the same time.
1 pod is located to the driver's side of the center console up high.  To 
access remove knee bolster and driver's center console side carpet. This 
controls the air scoop flap.

To repair the pods...George Murphy does sell a complete diaphragm repair 
kit.  The kit gives you two rubber diaphragms for those 'dual' elements 
that have a center housing and two ends each housing a diaphragm.  So, 
one pod - two diaphragms. These are for the recirc/fresh air elements.  
The rest are single element (just two plastic halves) each holding just 
one rubber diaphragm.  If your MB resided or resides in a really hot 
climate, just buy new elements from Jonathan, Rusty or MB as the plastic 
tabs that hold the pods together become so brittle that attempts to open 
the pod will result in one or more breaking.  That said, I have 
successfully repaired 4 MB's using the George Murphy kits.  Other's I've 
heard from have not fared as well.  Also the pods have plastic legs that 
twist on and off metal dash holders.  These legs can break if you are 
not careful too.

So, now you know the locations and number of pods in a 126 MB.  You 
really need to read and run the tests outlined in the MB Service Library 
under 83-601.  The tests can be done without an exotic tester by you 
without a lot of difficulty.  Just take notes and follow the steps in 
the order they are laid out.

Basically, if the pods have never been serviced, they are all leaking!  
But, all of the tests under 83-600 and  at a minimum 83-601 will also 
provide information on the condition of the switchover valve itself and 
the ACC push button control unit.  It's entirely possible they are in 
need of replacement.  Other issues or complaints that point to problems 
with the ACC pushbutton unit itself are- a dead short on the monovalve - 
resulting in permanent damage to the acc pushbutton unit.  A bad or 
shorted coolant recirculating heater pump - resulting in your blower 
demonstrating that it has a life of it's own; cycling on and off 
whenever it likes with you getting cold in the winter or hot in the 
summer because no air is moving.  Another sign of acc pushbutton trouble 
will be a rapid clicking sound in the dash.

FYI, the G Murphy repair kit is $50-60 currently. New pods are $60-80 
each currently.  A rebuilt pushbutton unit is $155-175, warranty 3 years 
BUT, you must test for mono-valve and recirc coolant motor conditions or 
warranty is void.

So, while it is likely all vac elements will need replacing, I recommend 
you go over the whole system first troubleshooting each component and 
then making repairs.

I have a document written by another MB member that provides the pin-out 
map and tests for the acc push button control unit and the vacuum 
switch-over valve. If you need it, ask and I'll email you directly.

Good luck,

Dick

Rick Granlund wrote:

> i-

> 89 560SEC

>

> I have the same problem!  All climate control buttons put the air to 

> the windshield only.  See below.

> Jonathan...anyone.....any ideas??

> Thanks.... another 'Rick'

> >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

>

> "Date: Mon, 26 Nov 2007 15:05:47 EST

> From: WRick11499 at aol.com

> Subject: [W126 Coupe] Heater & rear window defoger

> To: mbcoupes at mbcoupes.com

> Message-ID: <bda.1c8494cc.347c811b at aol.com>

> Content-Type: text/plain; charset="us-ascii"

>

> 1985 500 sec

> I need to know which relay is the rear window defogger

> also no matter which button on the climate control  I push, I still  

> get air

> blowing from the windshield defroster vents.  Has anyone had this 

> problem and

> how to fix.   Thanks  Rick

> >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

> The MB Coupes Website!

> W126 SEC Mailing List

> Postings remain property of MB Coupes, L.L.C.

>