MODERATOR'S NOTE: For an update on vacuum pod availability from MB and aftermarket sources, and pricing, please check this thread.
When I purchased my 560SEC 11 years ago, I lived in Portland, Oregon. Just prior to purchase of the car, it had been converted from its factory-issue R12-based ACC system, to R-134a. However it was a "straight" conversion, which didn't replace any of the critical components such as the compressor, condenser, receiver/dryer, nor expansion valve. The system was basically flushed, new fittings were installed, and the system was converted over to the supposedly more "enviro-friendly" R-134a refrigerant.
In Portland, OR, where the summer climate is generally quite mild, there is no need for regular / consistent use of the air-conditioning system except for the height of summer, and even then perhaps only for a couple of weeks. The R-134a system was OK in this usage; although it was never super-cool, it was adequate for the limited usage I gave it.
After I moved to Houston, TX in 2008, I quickly found that the R-134a system was inadequate for spring/summer/fall usage. Basically, A/C must be used in Houston around 9-10 months of the year when driving automobiles. It is particularly required during the May-October months. After suffering for the summers of 2009, 2010, 2011 and most of 2012 with the R-134a based system, I finally had enough and decided to convert it back to R-12. It helps that the cost of R-12 has come down dramatically from what it was 10-15 years ago, and there is plenty of it available when needed. In the meantime, the price of R-134a has actually gone up quite dramatically.
So, in September of 2012, I had my mechanic shop re-convert my ACC system back to R-12. At this time, they installed a brand-new compressor, receiver/dryer and expansion valve, and introduced R-12 fittings back onto the system. After this conversion, the system blew extremely cold air, which was welcome. However, during this September/October time frame, the summer heat was winding down so I had little to no chance to really test the system adequately.
Finally, the summer of 2013 rolled around, and the heat (as usual) got intense starting in late May. I was using ACC every day and it worked quite well. However, I had a problem during June and into July whereby the system would begin to blow increasingly warm air, particularly when running at stoplights and in traffic jams. I performed multiple tests and determined (using a spare Klima relay) that the A/C system was working fine. The compressor was firing when it should have; it was condensing water underneath the car, and the fittings underhood were sweating ... all this meant the system was working adequately.
Some additional tests of the system function showed that the "fresh air" flap, located behind the passenger-side airbag, was open all of the time and not closing when the A/C system was running. This meant that the system was pulling in hot outside air and mixing it with properly refrigerated air, making for a warm to mildly cool system -- particularly when the car was not moving.
Further investigation confirmed this -- there is a simple test to check the fresh air flap position / operation. With the engine running and the ACC system operating, you put your hand on the plastic air intake grill at the base of the windshield (hood open). If you can feel air movement at this grill when the A/C system is running, then you know that the flap is wide open and admitting warm air. A check with my 560SEL, which has a properly operating ACC system, confirmed this condition. This fresh air flap is controlled by a PAIR of vacuum pods, both with dual chambers, because a significant amount of force is required to move and control the rather large fresh-air flap.
Thus, the remedy for this was simple: replace the inoperative pair of vacuum pods that controlled the fresh air flap. Although these pods are fairly easily accessible by removing the passenger-side airbag, the more I thought about it the more I edged toward replacing all six pods in the system. As far as I could tell, with my records of the car, none of the other pods had been replaced save for one I had done in Portland by my mechanic there. So it was a relatively simple matter to just look up the part numbers for the pods and order them.
I checked the prices of the pods carefully. Four of the six are Behr pods (OEM) and are available for somewhat cheaper than factory pods, through AutohausAZ.com. Two of the pods are available for less money through parts.com. So, I ordered all six of the pods from their respective sources and vowed to do the job when the right time came.
- Fresh air pod #1 (short/gold arm): 000 800 57 75
- Fresh air pod #2 (long/silver arm): 000 800 58 75
- Defrost vacuum pod: 000 800 43 75
- Center nozzle vacuum pod: 000 800 67 75
- Leg room flaps vacuum pod: 126 800 14 75
- Scoop air flap vacuum pod: 000 800 40 75
- Medium-sized Philips screwdriver
- Flat-blade screwdriver
- Long or bent needlenose pliers
- 10mm and 13mm sockets, 1/4" ratchet with 6-12" extension
- handheld flashlight
- Mityvac or other vacuum tester (not required but helpful)
- 5.5mm 1/4" socket
- "stubby" Philips screwdriver
- cutter pliers
PART 1: Fresh Air Vacuum Pod Replacement
The first step is to put the passenger and driver's side seats back all the way in the their tracks, using the door seat-bottom switches. This will give you the maximum amount of room for working under the dashboard, which you will be doing on both sides of the car.
Next up is to disconnect the battery. This requires a 13mm open-end or box-end wrench on the negative battery terminal. Once loose, I just wrap it in several folds of a rag and set it on the battery so it doesn't make contact with the negative battery pole.
The next thing is to disconnect the airbag module, AFTER you have disconnected the battery. Remove the passenger side carpets, and use a 10mm socket on an extension to remove the nut that holds the passenger kickplate in place. Under the kick-plate you will find a number of connectors, including those for the factory alarm, the airbag connector (red colored), and the O2 sensor at the lower left near the edge of the carpeting. Notice that I disconnected the factory alarm (last photo below) many moons ago....
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Find the red airbag connector, and disconnect it. It pulls straight off.
Next up, you'll need to remove the passenger-side airbag. As with the 500E/E500, it is held by a 10mm long bolt that is oriented vertically and accessed through a hole underneath the dashboard. Your 10mm socket + extension used to remove the passenger kickplate is re-used to access this long bolt. Remove it. See how long it is?
Then, you can slowly work out the passenger-side airbag module using a CAREFUL back-and-forth motion. Unplug the two red plugs that are in the back of the two sides of the airbag, on the back of the module. Tuck the forked airbag power cable into the dash, below where the airbag sits, to get it out of the way.
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Here are a few reference shots of the airbag frame, which will come in handy when it comes time to reassemble the airbag and put it back into the dash.
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Although you don't need to do this for removing the two fresh-air flap pods, I opted to begin to remove the airbag frame as I am replacing all six pods and need the maximum amount of room to work. I also removed the under-dash tray at this time, as well. It is held by the three screws you see in the last photo above (located behind a trip strip) and two plastic "holder" screws below the dash near the hole to access the airbag long-bolt.
Next, I removed the plastic flexible tube that supplies air to the right-hand dashboard vent. This just snaps off at both ends (press-fit) and pulls out easily.
Now that you have some working room, you can lift up the fabric cover and expose the two pods that control the fresh air flap. As you can see, they operate the flap control lever in a "push-pull" arrangement to maximize leverage for this very large flap (which is visible in the background of both photos below, with the red number written on it).
To remove the pods, you need to pull off the two rubber vacuum elbow connectors on the pod's vacuum nipples. The green vacuum line goes on the top of the pod, with the red line on the lower connection. As you can see, the pods on the later (post-1985) W/C126 models use a "bayonet" mount, by which plastic tangs at the base of the pod are inserted into slots, and the pod is rotated about 15 degrees to "lock" it into the mounting base. You can see these tangs in both of the photos above, locked into the base. The lever also has to be disconnected from the flap control lever. This can be done with a pair of needle-nose pliers to GENTLY compress the end of the plastic ferrule, while using your fingers to LIFT the pod's lever clear of the ferrule. It's self-evident when you see how it works. The main thing is NOT to break the ferrule as it is old plastic, and very likely quite brittle.
Here are a couple of photos of me lifting the pods clear of the dashboard.
Here are the two fresh-air flap control pods, as removed:
And here are the old pods (light pink bodies), next to their Behr replacements (darker pink bodies):
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As you can see, the "factory" MB pod (see the last photo above, bottom (darker) pod with the multicolored label) is indeed made by Behr despite no outward indication on the MB labeling/packaging.
The manufacture dates on the pods that I pulled from the car were 89/20 and 89/30, respectively (May, 1989 and August, 1989) so they were the original pods. Not bad ... they lasted nearly 25 years !!!
Some additional checking showed that the short/gold pod (on the right side of the push-pull arrangement) was the bad one -- the upper chamber was not holding vacuum, indicating that the rubber diaphragm inside had developed a tear or hold that did not allow it to seal.
I will continue this series on pod replacement with Part 2 in the near future.
Hope you enjoy this and find it useful.