Most of the air blows to the defroster vents. I've been getting around this by blocking off the flow with pieces of hose cut to length, which moves the air to the front vents. However, with winter coming I need to fix this right. I removed the side panels on the console and found what I'll call the "vacuum control box" on the passenger side behind the radio. It appears that the CCU controls this box (labeled 1 thru 7) and directs vacuum to each pod as needed. I'm about to start pulling vacuum on each line to see what happens and if the pods will hold. That's about all I know to do. My service manual (on disk) has a tab for Climate Control but when I go there, there is no content. So I'm just stabbing in the dark here. Any advice and help on where to look or likely causes is appreciated. Thanks!

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1991 350SDL 350k+ miles

The FSM is also available online: Untitled Document

I would first suspect either a fuse or a loss of vacuum to the control box since it has failed to the default mode of defrost.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Thank you for the link. I have the disc, but the climate control section is blank. I checked the vacuum to the control box and it is good. I hadn't thought of a fuse, I'll check but I think they are all good (occasionally go thru box with a test light). Basically, the buttons are non responsive in regards to moving the air flow.

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1991 350SDL 350k+ miles

Go to startekinfo.com and look up the model 124 service info under MB workshop resources on the left.

Or go to w124-zone.com, register, follow factory service manual link, select the OM603 tab.

Chapter 83 explains it all.

Model 124 has the same climate control system as your car.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

The defrost pod is open by default, so it will stay open if there is a leak elsewhere. My experience tells me one of the pod is leaking, most likely the pod to the center vent.

This is what you can do since you have the side passenger panel open.

1) Remove the hose to each pod at the 'vacuum control relay' and pull vacuum. Do it one by one and all should hold vaccuum. Any line not holding vacuum is the culprit. Check the schematic for which one.

schematic here

2) It could also be the 'vacuum control relay'. Info here.

Control DIY here

3) Remove the glove box. Very easy job and you will see the glove box control Pod on the left. Check whether it closes, default is open position.

It is not an easy job to R&R the pods without removing dash and center sole. I had a leak with the center vent pod. This is how I 'fixed' it. I remove the center vent grill and jam the control flap insode open. A PITA job. I then plug the line from the control relay to that pod.

Good luck.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Thanks, that schematic of the vacuum system is exactly what I need. I've put it back together already, but I know that pods 7 and 5 are bad. 6 held. Then I had a problem with my pump so I didn't check the others. I know this is going to be a tough job, that is why I've put it off so long.

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1991 350SDL 350k+ miles