[W126 Coupe] Climate Control Air Flow Issues

[Dick Spellman]

Your welcome.  That was done on a late night in a New York hotel where 
sleep did not come easily.  Glad to help every once in a while. Here is 
the pin-out test info file from another list member at 
mercedeslist.com.  Another great group of folks, I might add.

Good luck in effecting the repairs.

Dick
Boston, MA

rltimmerma at cox.net wrote:

> Dick Spellman,

>         Thank you for your comprehensive climate control writeup,  I've saved it to my MB Coupe maintenance folder.

> I would like the write up you mentioned about the AC pushbutton unit.  E-mail offline to ray at tubeprocess.com

>

> Thanks again,

>

> Ray Timmerman

> '90 560 SEC

>

>

> ---- Dick Spellman <spell.yy at verizon.net> wrote: 

>

> =============

> 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

>>     


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