W124 climate control vacuum pod replacement - PeachParts Mercedes-Benz Forum

gsxr · #1 04-08-2002, 02:44 AM

Hi all, thought I'd share my recent foray into ACC repair:

Yesterday I replaced all the vacuum actuators (pods) for the climate control system in my sister's 1987 300D. Of the 6 total, only two are accessible without removing the dash - the pod for the floor vent flaps (pull the pushbutton unit to access this one), and the one for the defroster flaps (behind the glove box.) The other four - 1 center vent, 1 diverter, and 2 recirc - require pulling the dash. That means yanking the instrument cluster, steering wheel, p/b unit, glovebox, both lower trim panels, and then the whole dashboard. And then you need to pull off the top of the heater box to do the center vent & diverter pod, which is also a pain. This car (with 155kmi) had 4 bad pods: center vent, diverter, recirc (small lift), and defrost (small lift). Needless to say the system was NOT functioning as intended, although the ONLY symptom was a lack of air from the center vents with the A/C on. W124's are sneaky that way.

So, I've said it before and I'll say it again: If you own a W124, particularly one that's older or with high miles, you should check the operation of the pods to make sure your ACC is working as designed! It's easy to test. Pull the glovebox and the 7-port manifold is right there on the left side, attached to the heater box. Remove one hose at a time and connect a MityVac. Each hose should hold vacuum. If not, the rubber diaphragm for that pod is torn. You can identify the function from the ACC service manual, if you want to know what's not working (assuming it's not obvious). The pods from Rusty (or FastLane, etc) are ~$15-20 each for the single chamber ones (center vent, floor, and diverter), and $25-30 each for the dual chamber (both recirc and defrost). I've heard that George Murphy sells a diaphragm kit to repair the pods but I don't know details or pricing, or how hard it is to repair them.

It took me 2 hours to remove the dash, 1.5 hours to replace the 5 upper pods (I left the footwell pod alone), and 2 hours to reinstall the dash. Total was 5.5 hours. If you do this, I HIGHLY recommend replacing ALL the pods that require dash removal!!! This is NOT a job you want to repeat a few months down the road when the next old one fails. Change 'em all and then you don't need to worry about it for the next 10 years or 200kmi. The two exceptions are the ones that don't require dash removal; the defrost & footwell pods. These can be done at any time in 30-60 minutes.

Tips for installing: Leave the flat metal bars attached for the recirc pods. Undo the connector tabs at the pod and reconnect to the new pod. Most of the pods have a lock tab that must be pressed before they will rotate out (I learned that the hard way last time - don't ask.) The diverter pod is held in by 3 round metal press clips, so you need to break out the old one and save the mounting clips for the new pod. The center vent pod is the trickiest. Although the manuals says you need to pull the heater core (YUCK!) it is not necessary. Remove the white pin in the top door. Remove the door by flexing it out of it's hinges. Remove the flat metal rod from the pod. Pull the hose and twist the pod out, it will *just* wiggle out from under the mounting bracket. Oh yeah - just before you reinstall the dash, do the MityVac test one last time on all 7 hoses! Otherwise, if you forgot to connect a hose you need to repeat the 4 hour dash R&R job! (Oh, joy!)

For the record, of the three 1987 300D's I've tested, this is what I found:
=======================================================
Car 1 (155kmi) - bad center vent, diverter, recirc, and defrost
Car 2 (229kmi) - bad center vent, recirc, and footwell
Car 3 (238kmi) - bad diverter, recirc, and defrost

And a couple more 124's I've tested since the original post:
============================================
Car 4 (86 300E, 200kmi) - bad center vent, diverter, recirc, and footwell
Car 5 (87 300E, 110kmi) - bad center vent, recirc, and defrost

Part number list:
======================================================
124-800-00-75 = Defroster pod (dual chamber)
124-800-02-75 = Center vent pod (single chamber, twist-on)
124-800-03-75 = Diverter pod (single chamber, small, attaches w/3 clips)
124-800-04-75 = Recirculation / fresh air pod 1 (dual chamber)
124-800-11-75 = Recirculation / fresh air pod 2 (dual chamber)

124-800-01-75 = Footwell pod (round, small, to VIN A289309, 1986 to early 1987, two required)
124-800-09-75 = Footwell pod (rectangle, from VIN A289310, late 87 through 95, one required)

NOTE: Of the pods above, only the -02-75 (center vent) can be properly "rebuilt" using the diaphragm kits from Performance Analysis. The dual-chamber pods can only have the 'small lift' portion rebuilt properly. The diaphragm kits for the dual-chamber 'large lift' will restrict movement and should NOT be used... replace the recirc+defrost pods with new pods only! There are no rebuild diaphragms available of any kind (good OR bad) for the small round pods (diverter and early footwell), nor for the rectangle pods (late footwell).

Photos are at this URL:
http://www.w124performance.com/images/W124_dash/

Do yourself a favor - grab your MityVac, pull the glovebox, and check them out! Summer's coming up fast and a fully working ACC is a beautiful thing.

Best regards,

jwiggin · #2 05-01-2002, 04:33 PM

Dave:

I recently acquired a 1989 300E with 127,000 miles. The blower fan never seemed to go on high, but knocked softly instead. The knocking has stopped, but no high fan. I've been investigating that problem and today pulled the glovebox to see what I could see. I noticed that the pod behind the glovebox (you said it is for the defrost) does not activate unless I push the metal connector in a bit. Once in (when on a/c or economy) it will go back up as long as I do not let it go out completely (i.e. by putting the system on defrost, bi-level or off). Once all the way out, it will not go back in. Think this is a vacuum problem?

gsxr · #3 05-01-2002, 04:40 PM

Hi Jim,

That sounds odd. I'd test the actuator first, using the procedure described above (apply vacuum to both ports on the pod). Use a Mity-Vac if you have one, if not, use the source line into the top of the 7-way manifold with the engine running.
Note: With vacuum applied to one of the two ports, it will move a LOT. When applied to the other port, the movement is almost invisible. You can see it if you watch closely though. With a MityVac (the kind with a gauge on it), you want to make sure both hold ~25 inches vacuum. If the diaphragm is torn it won't hold any - dead zero, usually.

If your pod checks out, it's either something with the vacuum plumbing (not likely), or an electrical gremlin (more likely).

HTH,

anthonyb · #4 09-28-2002, 08:33 PM

Does anyone know what the diverter flap is used for? I pulled my glovebox today, and tested all the vacuum pods - this one and the recirc small lift are bad.

Symptoms are no air through center vents (center vent pod holds vacuum, but I can't hear any flap actuation), and low air volume - high blower sounds like high blower, but only puts out min blower air.

When I applied vacuum to the diverter pod, it wouldn't hold a vacuum unless I quickly applied more than 10" Hg, then it held, but slowly leaked. With the engine/fan on, I got lots of air through the center vents, but little through the side vents.

any ideas?

-anthony

p.s. Thanks for an excellent post, I've referred to it often enough that it gets bookmarked..!

gsxr · #5 09-29-2002, 12:58 PM

Hi Anthony,

Wow, that does sound odd. The diverter flap, from what I understand, allows a different airflow path through the internal coils. I'm not sure what the exact function is. I do know that if your center vent pod is dead, you can switch the signal to the diverter pod (if it's good) and get air out the center vents, otherwise your AC operation is poor with no center vent airflow. The side vents are fully open at all times with no flaps controlling them. If airflow is poor there, you either have a blockage, or the end vane piece (what you angle & adjust with your fingers) is not installed into the duct properly.

About the center vent, it will only blow cold air... with the heater on nothing comes out there. When you apply vacuum, you should be able to look through the center vent opening with a flashlight and see the "floor" drop away, revealing the AC evaporator (just barely visible). If you see no movement, your center vent pod is either dead or disconnected internally, or perhaps has a pinched/blocked hose?

Either way, if you plan to keep the car for a long time, I'd yank the dash and change them all. George Murphy sells rebuild kits which claim to work on single & dual chamber, however they do NOT work properly with dual-chamber pods. And the diverter pod is a different size, as is the footwell flap pod(s). That means of all the pods in a 124 dash, his kit works for the center vent pod only! Rather than mess with those, just get new pods for everything. I'm going to be doing my other 300D this winter (one of the 3 cars mentioned originally), and I'll be taking photos this time to document the process...

Regards,

anthonyb · #6 10-05-2002, 06:14 PM

Alright, well I figured out why I wasn't getting much volume through the air vents: the blower fan was installed wrong! (boy, do I hate doing the same job twice. At least it only took me two hours instead of eight...)

I still haven't figured out what the diverter flap is for, from the shop manual it looks like it only opens when the system is on 100% recirc, and lets a greater volume of air through the center vents, but it's closed on any other setting. Since I don't get any air through the center vents period, I think the diverter pod is dead, and the center pod must be disconnected (or otherwise broke) somehow.

I tried looking through the center vvents to see if I could detect any actuation of the center pod, but there's another flap in the way (the one connected to the thumbwheel on the vent itself).

Thanks for your help so far - if you do get pictures (!!!) on the dash removal, I bet a lot of people would love to see them. I know I will.

-anthony

gsxr · #7 11-21-2002, 09:25 AM

Hi again - I did my other car this weekend (third time I've done this job now.) Photos are at this URL. It took me 1 hour to remove the dash this time! I don't think it could be done any faster though... still takes 1.5 hours to replace the pods, and 1-2 hours to reassemble. Anyway:

http://www.w124performance.com/images/W124_dash/

Enjoy!

gsxr · #8 11-21-2002, 09:28 AM

I'll upload a couple that are small enough to get through the forum size limit, for those of you too lazy to click the link.

Here's a shot of the center vent pod, buried in the heater box, in front of the heater core:

gsxr · #9 11-21-2002, 09:29 AM

And here's proof that it can be removed through the top door, without pulling the heater core like the manual says. Small hands are required, if yours don't fit, find a helpful small child and bribe them with lollipops or something:

gsxr · #10 11-21-2002, 09:32 AM

Here's a photo of the innards. One obviously has lots of holes and is all torn up. The other one had hairline cracks near the wide bottom end, almost invisible until you start pulling on the rubber and find out it's not all one piece any more!

gsxr · #11 04-26-2003, 06:23 PM

Just a quick update to my original post (which I have edited). The vacuum pod rebuild kits sold by Performance Analysis company work on single-chamber, large size pods only. That means for the 124 it will rebuild the center vent pod and that's it. On a 123, same deal, center vent pod only (possibly the footwell flap, I'm not sure). The 124 diverter pod is smaller, and the older 124's have a rectangular footwell pod.

For the dual-chamber pods, the rebuild kit will fix the forward (small lift) section only. The rear (large lift) section is non-rebuildable! The kit has an interesting way to get around that, and it looks great, but DOES NOT WORK. It looks like it works, but when you apply vacuum and measure the rod travel on a new one (or good used one), compare that to the freshly rebuilt pod. The rebuild simply does not have as much travel. It all makes sense when you see it, but it's very hard to describe. That means if you use the rebuild kit, your pod won't fully open the flap it's connected to! And considering the amount of work needed to pull the dash & replace these things, you don't want to screw around. Buy NEW pods - for EVERYTHING - and replace them all at once. Believe me, it's worth it, and having the system work as intended is a beautiful thing!

Best regards,

aldedmon · #12 04-27-2003, 12:12 AM

Hello Dave,
Have you ventured into doing the evap.core on the W124's. I need to do this on both my cars. I am very mechanically proficient but need a little nudge as i am afraid of the unknown. How bad is this job. Can you walk me through it very high level...or just how to remove the dash. I have a MB tech that works on the side that supposed to be coming by this weekend to do both cars... Just R/R dash and Evap cores x 2. If I could already have the dash out I could save major dinero. If you say I almost home after removing the dash, then i may not even bother calling him. Please let me know. if its not too much of a bother, perhaps i could call and speak briefly with you and get the particulars if I have ?? with your brief outline. Thanks in advance

gsxr · #13 04-27-2003, 12:22 AM

Hi Albert,

I've never done the evap or heater core. I think you have to pull the heater core out to access the evap - not fun. Pulling the dash is not too bad, just tedious. THe procedure is in the factory manual, it's pretty basic. You will have a LOT of little parts, so have a workbench are or some place you can set each item & the screws for it separately. And it should be somewhere that it can stay apart for several days if required! Definitely replace ALL the vac pods while the dash is out, particularly the center vent pod. Photo of the heater box is here:

http://www.meimann.com/images/mercedes/W124_dash/top_removed.jpg

More photos:
http://www.meimann.com/images/mercedes/W124_dash/

Note that the pipes leading into the evap are also hard to get to, at the expansion valve, under the windshield trim , behind the brake booster. It's definitely a major procedure. I think you could do the dash removal yourself, if you follow the factory procedure carefully. Acutally pulling the core & evap is what I don't know about - I'd ask your friend and see what he says! Just curious, are you *sure* both evaps are bad? Maybe it's just a failed O-ring at the expansion valve? I don't often hear of evap failures on the 124 chassis...

Regards,

wbain5280 · #14 04-27-2003, 07:34 PM

Hey GSXR

I looked at your 350SD head replacement pics. Very impressive. Just for future reference, what is the part number for the new head? If I decide tog et one of those beastly engines, how will I be able to tell if the work has been done?

Regards

skaa · #15 04-27-2003, 09:13 PM

GXSR,
Nice pix !! Any ideas how I might clean mold/mildew out of my '82 300SD 126 core without taking the dash off to get to it? Everything I read says the core is buried too deep for casual access. I've taken off my blower motor and cleaned it out, but as the humidity of summer approaches, I can smell the mildew when the ACC is on. Any thoughts would be appreciated!

-----------------------------
Steve Kaa

1982 300SD (312k)

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