You might have a bad blower motor... they are known to eat brushes and need replacement by about 20 years or 200kmi. Less likely is the speed controller (aka 'porcupine') mounted under the fan, or the pushbutton unit.

The vacuum pods only control *where* the airflow comes out, not the temperature or fan speed.

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Dave
Boise, ID
Check out my website photos, documents, and movies!

GSXR

Is there a step by step to take out the dashboard? Im in the process of taking out the dashboard to fix the vacuum problems I'm having. Im only getting air out of the defrost mod. I have a 1987 W124 300D TURBO.

The '87 w124's have no passenger side airbags, so access to the ACC vacuum distribution block and the defroster's diaphragm is quite easy, by removing the glove box. Use a vacuum hand pump to diagnose open circuits. (an inexpensive and quite valuable tool to own!)

Elsewhere on this thread you'll see a link to a vacuum schematic and diagnostic steps for every possible setting. Take your time and write down your results.

I found that replacing just the defroster diaphragm and re-routing the center ones to the floor was quite effective in restoring usable function to the ACC system, albeit cheating a little. I capped off a couple of vacuum circuits that I abandoned. You can order the new diaphragms right from the shop forum sponsors - great value! Don't bother with rebuild kits - get new ones.

Removing the entire dash was more than I wanted to get into, so I simply abandoned the broken flap actuators that were difficult to access.

I drove my 1988 W124 wagon happily for another two or three years in this mode before selling it last year at 220K miles. Should have kept it. I loved that car.

Something to appreciate is the clever strategy of the engineers of this ACC system. The default of a total vacuum failure is to route all air to the defrosters - a good bet in cold climates! The default failure of the defroster control flap is to leave it wide open. You can still operate the car with a clear windshield even if your toes are cold, or hot.

Keep that nice car rolling!

Jerry

1) If the ONLY airflow you ever get is out the defroster and the end dash vents, that's a symptom of zero vacuum present... check for vacuum at the top of the 7-port manifold (with the engine running!). If there's no vaccum, none of the flaps will work.

2) As Jerry said, you can jury-rig things to make it a little better, if you don't have time to pull the dash. I swapped the center vent with the diverter pod to get cool air out the center dash vents... drove like this for 2 years before I finally pulled the dash and replaced everything (don't just change the bad ones, change them ALL.)

3) DO NOT get the rebuild kits - pretty sure I explained why earlier in this thread. Get NEW pods.

4) To pull the dash, you need the factory service manual procedure... Group 68, job 100. Here's a link to the PDF file online (3MB download) :
http://mercedes.braingears.com/124_DISC2/Program/Chassis/68-100.pdf

gsxr - great tutorial on pod replacement. It was tedious & frustrating (6 hours) but my vents are now all blowing properly. 4 pods were bad. I have a few additional questions that relate to my goal of having a properly functioning ac system.

1. How can I tell if my evaporator is bad? I don't want to reassemble the dash if it's bad.
2. How do I test for no freon leaks on my 134 ac system? Can I use my trusted Might Vac? I've got to replace the receiver / drier (INDY shop charged system a year ago I told me that's why it gets cool but not cold) because it's not blowing cold & thus replace freon but I wanted to test for leaks prior to removing rec./drier.
3. I can spin the front wheel of the compressor so I'm assuming it's good. Can I add compressor oil without removing the compressor? How do you know if the compressor is engaging.
4. Should I go ahead & replace the expansion valve also? I think it's the original but not sure?

Sorry to pepper you with random questions. I've read a number of post on how to charge system but this will be my first full ac rebuild & thus I'm a little lost. Not to mention I truely don't understand the function of all the various main components (rec./drier, exp. valve, evap, freon, comp., etc) that make up an ac system.

I'm not GSXR ..But:

1. How can I tell if my evaporator is bad? I don't want to reassemble the dash if it's bad.
Visually is there signs of oil residue? That would be leakage.

2. How do I test for no freon leaks on my 134 ac system? Can I use my trusted Might Vac? I've got to replace the receiver / drier (INDY shop charged system a year ago I told me that's why it gets cool but not cold) because it's not blowing cold & thus replace freon but I wanted to test for leaks prior to removing rec./drier.

You can recover the freon, add dry nitrogen to 200# with a bit of R-22 and it will be easy to sniff test for leaks. Beyond that, you should charge the system.

3. I can spin the front wheel of the compressor so I'm assuming it's good. Can I add compressor oil without removing the compressor? How do you know if the compressor is engaging.

You can add oil with the compressor running via the low pressure line (adapter), or even put a squeeze type 1 oz charge (auto zone). If you've got the system open and replace the R/D replace all the o-ring seals and add oil to the dryer plus maybe 1 extra ounce. I don't have the system component capacity handy.

4. Should I go ahead & replace the expansion valve also? I think it's the original but not sure?
You should learn the functionn of all the components. This is not really difficult system. Pump, valve, evap, condensor and a R/D. If you take the system open, I'd put a new expansion valve in it - I got one at the dealership last week for my W124 and it was $44.

I've got a leak in mine- unfound, but a trusted pro checked the evaporator last charge. Now this past week, pressures didn't work out and it's most likely a failed Expansion valve. I'll recover the freon-then...
I'll do o-rings, flushing the system(coils), expansion valve, get the manifold rebuilt, and back flush it first. New oil, dryer and if needed compressor seals. Pull a hard vacuum for 2-4 hours and if it holds. Charge it back up with 1200g of R-12.
Hopefully that will put it in place. I'll look the condensor over really well for oil residue- but I'm guessing an o-ring on the compressor manifold hose.

Michael

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Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E

Hi all!

Thanks for the great write up on testing the pods.

I have no or largely delayed air to the floot vents. Every other vent works normally as changes fairly quickly (within 30 seconds).

I pulled the glovebox and tested all of the pods. They all checked out ok, including #3 footwell flaps. I even tried it with the car on, and the flaps changed over right away on the MityVac.

Does this mean my pushbutton unit is bad? Or where can I go from here?

Thanks for any advice. 1992 300D 2.5 Turbo, almost 230k.

-m

PS: My pushbutton unit is a 124 830 3185 part number

__________________
Now:
2018 Tesla Model X
1999 S500 Grand Edition 164k
1992 300D 2.5 Turbo 287k
2005 E320 4MATIC wagon
1991 Alfa Romeo 164L 99k (sleeping for a while)

Then: 96 Lincoln TC, 93 Lincoln TC, 87 560 SEL, 87 300 SDL, 80 300D, 89 560 SEC

The footwell flaps only open when the heat is on. I'm assuming you don't get any heat out the footwell flaps. In that case, since you've proved the vacuum portion is good...

1) Are you sure there is vacuum present at the top of the 7-port manifold, with the engine running? If not, find the broken or disconnected vacuum line in the engine compartment.

2) The 7-port manifold might be bad. This would be harder to test, you'd have to find the wire that corresponds to the footwell flap outlet, and check for voltage when the heater is on.

3) If the signal from the PB unit is correct, then it's probably a bad pushbutton unit. The part number you provided is correct for that year/model.

__________________
Dave
Boise, ID
Check out my website photos, documents, and movies!

Hey gsxr,


1. I assume so as all of the other flaps work properly.

2. Ok, I have the CD for the car, I can try to track that down.

3. Anyone have a spare pushbutton unit in Minneapolis, St. Paul, I could borrow?!

Thanks for the troubleshooting. I'll dig futher.

-m

__________________
Now:
2018 Tesla Model X
1999 S500 Grand Edition 164k
1992 300D 2.5 Turbo 287k
2005 E320 4MATIC wagon
1991 Alfa Romeo 164L 99k (sleeping for a while)

Then: 96 Lincoln TC, 93 Lincoln TC, 87 560 SEL, 87 300 SDL, 80 300D, 89 560 SEC

I wonder why the recirc flap has two big vacuum pods that move in unison. Doesn't seem like it would need two.

__________________
2012 E350
2006 Callaway SC560

BTW, in the factory ACC manual there is a four-step process to check the different vacuum circuits without removing the glovebox.

If you find a problem you then remove the glovebox to test the individual pods.

__________________
2012 E350
2006 Callaway SC560

This seems like too simple a question for this impressive review, but I can’t resist asking the question, since I am sure you will know what my problem is.

I get a very loud slapping sound from the center of the dash when I start my car with my climate control set in “auto” mode. It does not slap if I keep the control set to low fan. Is there something that would cause my vents to slap shut with such a loud noise?

I suspect it may be some kind of a vacuum thing, but it would be great to have a definitive answer and a possibly a little direction about a possible remedy.


Thank you for your help

__________________
I just couldn't give up on my 1995 E320.

I think it might be like always going back to that same bad relationship with an ex girlfriend.
You feel you love them too much, or you are just too stupid to know any better.



Flickr slideshow of my 1995 E320
http://www.flickr.com/photos/24145497@N06/sets/72157616572140057/

SOunds like the vaccum check is in order.

My problem is simpler, uh, doh, my 95 W124 DONT HAVE A GLOVE BOX!

I beleive it was "commandeered" for the SRS airbag.
Yes?

It sounds like the main air flap is closing. But, I don't think it should make a noise like that. I wonder if one of the pods going bad could cause that? Hmmm. Wouldn't hurt to pull the passenger airbag and check the 7 lines, see if they hold vacuum when tested with a MityVac. Does it do the same thing if you are in "EC" mode or not?

Yes. To remove it:

1) Disconnect the negative battery cable
2) Pull up the front carpet under the passenger's feet
3) Remove the 1 screw holding the plastic or metal shield in place
4) Unplug the big red connector (this is for the airbag system)
5) Unscrew the one long bolt that holds the airbag in place (bottom/center)
6) Pull airbag forward, unplug connector
7) Installation is the reverse of removal.

__________________
Dave
Boise, ID
Check out my website photos, documents, and movies!