Mercedes W123 Maintenance

Mercedes-Benz W124. Mercedes-Benz W124 – a series of business-class cars of the German brand Mercedes-Benz, which was produced in 1984-1996. It was first introduced in 1984 and was intended to replace the models of the W123 series. MBZ Parts specializes in Classic Mercedes-Benz OEM Used and New Restoration Parts, plus Aftermarket Upholstery and Maintenance parts. Specializing in diesel Mercedes and in all parts from '70s and '80s classic Mercedes vehicles: the R107, W123, W126, W116 and W115 chassis, as well as parts for the W108, W109, W110, W111, W112, W113, W114, W120, W121, W124, and W201 chassis Mercedes-Benz. August 12th Update – A Mercedes W123 300TD listed for under seven large selling in only a few days is further proof great finds priced to sell will not last long! Among our favorite station wagons to feature are great examples of the Mercedes-Benz W123 300TD Estate such as this silver over blue leather example listed recently on Craigslist in Attleboro, Massachusetts with an asking price of.

I haven't had time to post some of the older tasks I've done, so I'll just jump in with what I'm doing these days...

Task and Diagnostic Procedure

This task about repairing my automatic climate control unit (the ACC). These have a typical failure mode were some internal solder joints break, rendering it partially functional. Different units break different solder joints causing different failure modes, but one of the most common is that only defrost works, and often only works for a while after starting the car. This was exactly how my car worked. The non-technical diagnostic procedure is to wait until the ACC is in its failure mode, and then give the front of it a whack to see if it starts working again for a bit. On mine, that would cause defrost to start working again, for a while at least. Note that there is another unrelated failure mode where wiggling the ignition key restores functionality for a while -- if yours responds to this procedure, then this repair probably won't help you.

Repair

The repair for this unit was to use a soldering iron and reflow (remelt) the solder. To get to the joints requires disassembly of the unit, so that's what we'll do.

Tools Needed

To do this repair, you'll need the following tools:

Flat blade screwdriver
Phillips screwdriver
penknife (my tool of choice for easing click-together plastic latches apart)
needle nose pliers
soldering iron
rosin-core electrical solder

Steps

Step 1: Remove the fancy wood-grain front. I don't have a picture of this, but it is held on with friction pins that fit into the holes circles in
red. Above the radio (the radio bezel may have to be removed to access them), are two flat-blade screwdriver slots in the the bottom of the bezel for you to
gently pry it off with. The friction pins fit into the holes circled in red in this picture.
Step 2: Remove the unit from the car. There are two screws (circled in green) that need to be removed. After that, on the w123, the unit will hinge
forward on its bottom edge until you can lift it out. There are two large multi-pin cables attached, one on each side, that need to be
unplugged from the unit.

Step 3: Remove the front, plastic mounting bracket from the unit. Three screw (circled in purple) hold it on.

Step 4: Next, remove the temperature wheel It plugs into a set of pins on the side of the unit like the cables did, and has some little plastic tabs
holding it in place. Gently (!) squeeze the two white plastic tabs together using a needle nose pliers just enough to get them to slip down
the hole (see orange circle and arrows) and ease the temperature wheel unit off. Don't force these tabs, and don't squeeze them together too hard or that 20 year old plastic will break.

Step 5: Remove the cover of the fan switch unit. The switch unit can't be removed yet because the buttons lock it to the front piece. Taking the
cover off makes it easier to remove the buttons. The cover is held on by two tabs, one on the top (see purple circle) and one on the bottom.
Gently ease the cover off past the tabs. I prefer a penknife for these kinds of operations as they are thin enough to slip between the plastic
parts without mashing and marring them too bad. Just be careful not to slice pieces of plastic off.

Shown here is the unit with the temperature unit removed and the cover of the fan buttons removed.

Shown here is the inside of the fan switch unit. The 'T'-shaped piece of plastic is held in by the cover. If it fell out when you removed the
cover, this picture should help in getting it back together correctly when you reassemble. The round pivot in the middle is different lengths. When you reassemble, just be sure the fingers of the 'T' fit into the backs of the switches like shown here.

Step 6: The next step is to remove the buttons and the front piece. The way I did this, they sort of need to be done together -- the front piece can't
be removed until the buttons are off, and I couldn't figure out how to pull the buttons off so I had to pop them off from behind, which I couldn't do until the front piece was off. The next two pictures show where the tabs that hold the front piece are -- here is one on the top (circled in blue) and two on the bottom (circled in blue on the next picture). Pop them them apart, but the front piece can't be removed yet because of the buttons. However, popping it free allows just enough access to slip the penknife in behind it and pop the buttons off by pushing them from behind and shown in the next picture. The fan buttons can be easily popped off by pushing from behind.

Shown here are all the parts removed so far. The rest of the disassembly is pretty easy from here on. Note also the clear plastic light pipes across the front and down the side of the fan switch unit.

Step 7: Next remove the bottom plastic panel. I've reused an earlier picture to show where the three tabs on the back that hold it on are. Once released, it hinges up toward the front until it can be removed.

Step 8: Finally, with the buttons off and the front piece removed, the fan button unit can be removed. Press the two tabs by the purple arrows together just until they clear far enough to slide out and allow unplugging the fan button unit from the side of the climate control unit.

W123 Mercedes Parts

Step 9:The plastic cover over the internal circuit cards can finally be removed. The circuit cards and guts hinge down and out from under the cover. Once the cover comes off, the two plastic pieces with pin numbers that the side pins stick through can be slipped off.

And here's the wrong ACC unit in all it's stripped glory -- yours from a w123 won't look exactly like this one (this one's from my practice w126 unit). There's a main base board, the top daughter board, and the two side wing boards with the pins. BTW, the w123 unit only has 4 relays instead of the 6 shown here, and the circuit traces are slightly different, but otherwise they look pretty much identical.

The Repair

With the unit disassembled, the repair can begin. Some have reported that they had cracked circuit traces on the daughter board where the pins from the front panel switches connect. Mine were fine there, but had cracks where one of the wing boards connects to the main board.

Shown here are the cracked solder joints on my unit, circled in red and with arrows pointing to them. I've even slipped a small piece of yellow-green paper down one crack to prove to myself that it was indeed not connecting reliably :). The solder on these needs to be remelted with a soldering iron, and maybe a little more new solder added, to rebridge the gap.

And here's the repaired solder joints, circled in blue.

Failure Analysis

Mercedes W123 Coupe

I'm certainly not officially qualified to do a failure analysis, but I've had years of experience taking things apart and fixing them, often trying to make them better so they won't just fail the same way again. So, as long as I was in there, I figured I'd take a look and see if I could figure out why those particular solder joints had failed on my particular unit. Sure enough, there was. When my CCU was soldered together, the wing board with the cracked joints was bent and the solder was used to hold it in place. This put permanent tension on the solder bridges. Unlikely that the tension alone caused the failure -- it was probably the the vibration of the car and that heavy cable hanging off those pins that did it. However, the tension made them spread once broken and certainly helped propagate the cracking down through more of the bridges.

A Better Fix

Using lead solder as a mechanical attachment isn't a great idea as it tends to bend, stress fracture and disconnect. I tried using it for that a lot as a kid and it always failed in short order. So how to fix it to be better? Replace each solder bridge with a small length of stranded wire. Make sure that the solder doesn't bridge the gap so there is no mechanical attachment via it -- if there is, that bridge could break such that both ends of the wire are on the same side. I certainly didn't do this. Instead, I completely unsoldered that wing board, repositioned it so I wouldn't need to flex it as I resoldered it, and then made new solder bridges to hold it on. I figured the bridged on the other wing board (the one not flexed) had lasted 20 years, so this would probably be good for another 20 years now.

I also went a bit further and reflowed all the solder of all the joints on all the boards. Sometimes solder joints can have pratically invisible cracks through them in my experience. I figure it was easier to reflow all the joints then have to disassemble the unit again to repair some other failed joint.

Mercedes W123 Amg

Reassembly

I didn't take any pictures because there was nothing interesting. Just reverse the disassembly steps and it all clicks together. At the time I did mine, I didn't clean the pins and reassemble with dielectric grease, but that might have been a good idea. The only tricky part I has was remembering how the buttons went back in. They all have a side were the clear plastic inside them is exposed on one or more sides -- make sure you pop them back on such that the exposed clear plastic edges face a light pipe (I don't think they'll go on wrong, but I didn't try).

Mercedes W123 230e

Mercedes-Benz W124 Service Manuals Free Download

Mercedes W123 Maintenance Manual

Title	File Size	Download Link
Mercedes W124 ETM(Electrical Trobleshoot Manual) PDF.rar	49.9Mb	Download
Mercedes-Benz W124 1985-1993 PDF Repair Manual.rar	65.3Mb	Download
Mercedes-Benz W124 1985-1995 PDF Repair Manual.pdf	93.4Mb	Download
Mercedes-Benz W124 1985-1995 Service Manual.rar	185.5Mb	Download

Mercedes-Benz W124

Mercedes-Benz W124 – a series of business-class cars of the German brand Mercedes-Benz, which was produced in 1984-1996.

It was first introduced in 1984 and was intended to replace the models of the W123 series. In 1995, the W124 sedan car lost its place in the Mercedes-Benz model line to the next generation of the E2 class W210; cars with station wagon (S124) remained on the assembly line of factories in Sindelfingen, Bremen, Rastatt before April 1996.

In order to reduce the risk of reducing attention to the new line of business-class cars, Mercedes-Benz decided not to introduce the W124 series at the Frankfurt Motor Show in September 1984, where other brands also brought their own new or updated products. Instead, the new Mercedes-Benz W124 series debuted at the Seville Auto Show (Spain) on November 5, 1984 in a sedan with seven types of engines: 200, 230E, 260E, 300E, 200D, 250D, 300D. Deliveries of orders to customers began in the first months of 1985. Within the framework of this model, the most advanced developments of its time were introduced. The bodies of the W124 were distinguished by the most perfect aerodynamics due to the plastic molding for directing air to the car, fuel consumption and noise level from the oncoming airflow were reduced. On the windshield was installed only one janitor, the mechanism of which was designed to cover the maximum area of the glass. Also worth mentioning is the heating of the reservoir of the washer, the area of the wipers on the windshield and the nozzles with the help of coolant. And also electroheating nozzles of sprayers of a washer fluid. The rear headrests reclined at the touch of a button on the front console to improve visibility through the rear window. For models with four-cylinder engines, a four-speed manual gearbox was offered as standard, and for six-cylinder engines, a five-speed manual transmission was offered. By order, it was possible to install a four-speed automatic gearbox.

In September 1985 at the Frankfurt Motor Show was presented a variant with a body wagon (internal index S124). Cars were delivered in five and seven-seat variants. In the seven-seat version, the seats were folded in such a way that the luggage compartment had a flat surface. Both models also had a folding second row of seats, which increased the luggage compartment to 2 meters.

In March 1987, the Geneva Motor Show presented a coupe version (internal index C124). The coupe features a relatively high rear part of the roof (which made it possible to feel comfortable in the rear passengers) and wide moldings, painted in contrast to the basic color. In April 1987, the 300 TE 4MATIC was launched. Production version 300 TD (Turbodiesel) and its all-wheel drive version 4MATIC began in August. A year later, in 1988, the lineup of the series was replenished with two new models – 200E and 250D Turbo. The two-liter injector engine at 200E was previously installed on a similar model of the W201 series for the Italian market, and the turbo diesel version was indeed a novelty. At the Paris Motor Show in 1988 debuted model 200 TE. At the same time 300 TD Turbodiesel was equipped with a modified engine. Due to optimization of the combustion process, emission reduction was achieved. In the same year, from September, the anti-lock system and the heated exterior mirrors go into the category of serial equipment. The series also receives the same system as the S-class, the washing system of glasses: heating the reservoir with liquid and heating the nozzles of the sprinklers. Model 230E was equipped with vented front brake discs. Since November of the same year, the height of the car for all models except for universals and all-wheel drive versions has been reduced by 15 mm.

In September 1989, the 300D Turbo and 300D Turbo 4Matic turbo-diesel models were added to the three available all-wheel-drive models (260E 4Matic and 300E 4Matic, 300D 4Matic) at the Frankfurt Motor Show. Externally, the model with turbodiesel could be distinguished by a series of narrow slots on the front right wing (for air intake). In the same year, the Intra-corporate program “Diesel-89” was put into operation. Within the framework of this program, since February 1989, all diesel models of all series have been equipped with significantly improved diesel engines with new pre-cameras and improved fuel injection pumps. All these measures allowed to reduce the smokiness of the exhaust by 40% and to release the engines without particulate filters to the US market (where the strictest rules were in effect at that time). The power and torque of the engines slightly increased. As an additional means to reduce the emission of harmful substances from diesel engines, a specially developed very effective catalyst began to be offered since 1990 (names of models with a catalyst were marked with the prefix “KAT”).