I have a 1984 300D Turbo Diesel, which is quite nice, but no air comes out my center vents no matter what mode the climate control system is in. I believe the culprit is the Center Vent Vacuum Pod, but I have seen many methods for getting at this and would like to know the "best" way to attack or test it without having to remove the dash. I am fairly new to working on cars in general, but I would like to give it a go (maybe replacing that door lock gave me a false sense of confidence ).

Thanks in advance for any help you might offer.

EDIT: Found where I can buy the pod, quite well hidden...

Bump!

That's just how the system works. On my car (manual climate controls) you slide a switch below the center vents for fresh air. I believe the auto climate control cars have a similar switch.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

No they don't. You can remove the glove box and get to the pod and flap, unhook it, and prop the flap open so you can control the center vents at the vents themselves. Sorry I can't be more descriptive but I did this while crossing through southern Arizona in the middle of the summer with the gf driving a couple of years ago. It made a nice difference in the cooling of the car.

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Seth

1984 300D 225K
1985 300D Donor body
1985 300D Turbo 165K. Totaled. Donor Engine. It runs!!!
1980 300SD 311K My New Baby.
1979 BMW 633csi 62K+++? Dead odo

Well, the good part is that I have a while before it gets hot down here in Texas.

I hope to get a new pod and have it working as it should, as I like the configurations the pods use for different modes.
The one thing that I would like to ask about now is whether getting one of the vent covers off would help and if so, how to get it off. I think I have seen this mentioned in quite a few places and would like to know if it helps and how... I really don't see how you could access the area back there from the pictures of w123s with the dash off that I have seen, but then again, I really don't know what I'm doing all that much. I'm just handy with a screwdriver and taking things apart from building/repairing computers.

Unless you have long E.T. fingers and a few extra knuckles, you are not going to be able to remove the pod that needs replacing, unless you remove the dash. The pod that you can see on the left (once you have the glove box out), closes the flap at engine shut-down - the one that opens it back up, is waaay in the back of the box, against the firewall.

Once you open the flap with the lever/pod on the left, fasten it somehow to fix it in place (so it can't be moved). Although this leaves the vent permanently open, you can shut off the air supply at the vent outlets themselves (the swiveling things) twist them either clockwise or counter-clockwise for open/close.

PS: as far as your a/c goes, do a search - you will find lots of info, and how to test a few things without any fancy gadgets.

Good luck!

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It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein


09 Jetta TDI
1985 300D

The following applies to the 1981-1985 300D, 300CD and 300TD with automatic climate control:

The vacuum line that leads to the "Center Flap" actuator also draws vacuum from the "Defroster Flap" actuator on the SHORT RUN connection (in other words, the vacuum line has a 3 way connector near the Center Flap actuator which feeds another vacuum line that leads to the Defrost Flap actuator Short Run). The Defroster Flap actuator is known to fail early (the replacement actuator is an improved model). So....before going through all the effort to replace the Center Flap actuator, it needs to be tested. This can be performed by either blocking off the vacuum line to the Defrost Actuator Short Run connection where the 3 way connector is located (next to the Center Flap actuator) OR disconnecting the vacuum line at the Defrost Actuator SHORT RUN which is located on the left side of the black heater exchange box (behind dash). This requires removing the vertical carpet panel on the left side of the console for access and lower panel which the steering column passes through. I think it would be easiest to block it at the Center Flap actuator 3 way connector so only vacuum is drawn from the Center Flap actuator. You could then block the line to the center flap actuator and see if the Defroster Flap actuator SHORT RUN is working.

In case you are not aware....the Defrost Flap actuator has "two" vacuum connections were are independent of each other (this is the only climate control actuator with this configuration). When no vacuum is applied to either connection, air blows fully out of the defroster outlets. The LONG RUN pulls the Defroster Flap completely shut, while the SHORT RUN pulls it partially shut. When the climate control system is cooling the car (with the middle button engaged...not "EC" or the two towards the left) and the desired temperature (set on the temperature wheel) is more than 3 degrees than cooler than the actual interior temperature (or the temp wheel is set at "MIN"), the system is trying to cool MAXIMUM and blow all air through the dash outlets only. The vacuum switch to the Defroster Flap actuator LONG RUN is engaged, which pulls the defroster flaps completely shut. Vacuum is also applied to the Center Flap actuator and the Defroster Flap actuator SHORT RUN (since they are on the same line)....except the long run overrides the short run on the Defroster actuator. As the interior cools down and gets within 3 degrees of the desired temperature set on the "temperature wheel", the vacuum switch to the Defroster actuator LONG RUN shuts off. Now only the SHORT RUN works, which allows a small amount of air to release from the defroster ducts, along with the center ducts. At this point, the system also allows fresh air (versus recirculated air) to take over.

I hope this somewhat makes sense, as I am writing all of this from memory. I am at work and don't have my manual with me.

__________________
All the best,

J. P. Mose
1968 250SL
1970 280SE 3.5 Cabrio
1987 560SL
1990 560SEL

After removing the glove box, I do see the pod, waaaaaay back there, and I can see that there is a three way junction that attaches DIRECTLY to it, and I believe that the vacuum cable going down is from the controller and the vacuum cable going up is to the defroster.
The issue, as Larry said, is getting to it. Even testing the vacuum lines, I'm afraid I couldn't get hem back on if I took them off the pod.
I suppose I might as well go all the way and take off the dash to test and replace all the pods I can see/get to, although that will be during the summer when I'm out of school (I'm a high school student).

Anyone know of a good guide for this? I will be googling it, but all the guides I have seen so far have been for different chassis.

After looking at some dash removal/reinstallation guides, I have decided that quite frankly I would kill my car trying to do it.

I don't have the experience at all. How do I remove this panel?

I've replaced easily a couple of dozen W123 center duct pods over the years, and it's really not *that* bad of a job with the dash in. (Don't get me wrong, it's not exactly all roses and kisses, either.) You just have to take your time... and hopefully not have very large hands. It can be done nicely, without harming or bending anything, tearing the insulation, etc.

If you don't already own one, get yourself a vacuum gun. You can easily test the flap itself, as well as making sure you have vacuum *to* the flap in the "normal" cool-air modes. (Just to be certain we're on the same page, the center duct flap is supposed to open only on the normal or EC setting, when cooling. They're also supposed to open occasionally for very brief bursts in the other modes.) Sometimes you'll encounter a defective SOV or the like, and there's simply no vacuum being diverted to the pod.

IMHO, the most difficult part is removing the old pod from its 3 mounting posts and retaining washers. You'll usually destroy the old washers if you try to pry either the pod or the washers off. My solution (necessary if you don't have new retaining washers) is to carefully break the 3 plastic posts from the old pod. It'll come right out that way, plus you can re-use the old clips, since you then simply slide them right off the broken posts. (This might sound a bit hard to follow, but will make sense once you check it out.)

Another thing, you may find it easiest to go in through both the cluster and glovebox liner areas.

Good luck, with a little patience it can be done... and you'll feel much better when those center ducts "fire up" like they're supposed to.

cheers

Actually, I found today that it may not be the center pod at all.

I had the car in economy mode and set the climate control know all the way to minimum. According to the manual, this should have it blowing outside air in at blower speed 4 (the blower was set to automatic). Nothing happened. I put the blower on high. Nothing happened.
Once the engine warmed up, however, it started blowing warm air that seemed like it was heating up, the standard behavior for when the climate control system is trying to heat the car.
WHAT THE??????

Now I'm really lost.... What could be wrong here?
Must be a control system failure somewhere, but I don't know how this part of the system operates. I know that depending on the mode, the system applies current to switches that allow vacuum pressure to the flaps and actvate the fan, but I don't know what is applying the current to those switches.
If I am wrong, please correct me. I know I'm a noob and I'm trying to learn.

Sounds like your mono valve needs to be rebuilt....an easy job...the rebuilt kit just went up to $55 from popular vendors (as I need to do mine and it was $39 last week)

Read the following for the W126 chassis, which has the same mono valve:

http://mbdieseldiy.tripod.com/monovalve.htm

__________________
All the best,

J. P. Mose
1968 250SL
1970 280SE 3.5 Cabrio
1987 560SL
1990 560SEL

I am hearing from my dad that either I or him somehow broke the thermocouple, but even if it was broken, it wouldn't affect the system when it was set to min or max, would it?

At min, the climate control unit is suppose to default to maximum cooling, despite the interior or ambient temperatures. Max should be the opposite, maximum heating. Now I will say that last July, when it was in the high nineties (F), I didn't get heat at MAX, even though I had just rebuilt my mono valve and completely resoldiered my climate control unit (and replaced all but two vacuum pods)....this was all performed on my 1987 560SL (Hilda). So, perhaps extreme cold or hot temperature conditions can signal the system not to exaggerate the condition any further...but I really don't know if is just a fluke (I do know for sure that the compressor will not engage if the ambient temperature is below a certain level).

I know a lot about the climate system off the top of my head....how? I have driving either a W107, W123 or W126 for over twenty four years. I like to tinker with it myself and have read a lot over the years. Hence, I would start with the reading and gradually you will know it "like the back of your hand"!

Here is a good place to start:

Climate Control:

__________________
All the best,

J. P. Mose
1968 250SL
1970 280SE 3.5 Cabrio
1987 560SL
1990 560SEL

Well, I found that the climate control system was leaking vacuum and went to attack it and found that that the "circulating air pod" on the far right under the dash was dead and that the pin connecting the center vent pod to the flap was missing, although the pod was in perfect working order.

With a new diaphragm in that pod, the climate control system is in working order vacuum-wise, but in putting everything back together, I hit a snag.

How the heck are you supposed to get that rubber piece that connects the center vents to the center duct on?
It's a PITA to do anything with it. Is there something I'm missing?
I have the right vent out, and its still a huge pain.