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I can't remember how I did it, but I think if you push a wooden tooth pick at the cyan/blue arrow, the latch will lift up.
The pinky I dont recall I slide it backwards, but you can try.
One more thing.
The foam overtime become "powdery", apply something similar, or else you will get small minor vibration at times from the cable/connector hitting some hard component.
The foam is basically a tight-fit assistance for cable to sit pretty.
It seems to open this connector, you need to slide down the latch #1, then press the Tab #2 while gently spreading both ends a part.
The latch is simply used to jam the tab.
The tinny tab is used to clear a locking tooth.
It may be a good idea to vacuum all the crumbling foam dust before it finds its way all over the place.
I used a toothpick to gently cleanup the miniature fan so the fan wheel does not wobble afterwards.
Odd Temp Value:
Why is this system presenting eroneous temperature? When the temperature sensor does not see airflow, the software pegs the temperature to an extreme -50°C value ... or the tinny sensor has failed and needs an unknown 10¢ thermistor, or a diode junction or OCP replacement??
Who knows how long this fancy sensor is designed to last before requiring service ??
Save time by testing the reported temp. before reassembling your whole OCP unit. It also happen to control the sliding sunroof so expect to clear a related fault there and the mBrace emmergency buttons... Not a problem.
+++++ BONUS Gear Lube:
While you're up in the OCP cavity, take this opportunity to lubricate your sunroof motor before it chews up its soft gear drive.
I used brake silicon lube so it stands summer heat without petroleum grease evaporating again.
Last edited by CaliBenzDriver; Aug 25, 2021 at 07:36 PM.
Dang, now that Cali mentioned sunroof....I remembered something important. It may apply to non Pano Roof too...maybe.
Mine is Pano roof. When I disconnected* the pano roof control, the Pano roof auto closed itself. So be careful where your hands or tools are yah.
*NOTE : My Pano roof was 100% open when I disconnected the buttons/controller, as I wanted to have room to work removing roof liner.
I am only familiar with my regular sunroof. I bet the pano design is a bit different in the way it is built.
The sunroof single drive motor is located in the center above the OCP and directly wired to it. As you get the OCP removed, the actual sunroof motor looses its power connection.
I guess... the pano motor may be located at the back closer to R-SAM and remotely controlled by LIN/CAN.
When loosing OCP buttons, it defaults to its closed position to give you a surprise haircut💈
FYI: don't quote me here... I recall seing the OCP/Sunroof diagram showing the GND located all the way in the trunk, on the driver side, shared with RFK.
I thought this was a counter intuitive choice or a way to introduce voltage drop.
Last edited by CaliBenzDriver; Aug 25, 2021 at 08:36 PM.
Thanks so much Cali and S-P, your posts are so wonderful.
One more update: scanned again yesterday, scanner detected -50C from N70b1 temp. sensor when nothing unplugged. Today, I take out fuse #17 from fuse box (to stop any power to the entire OCP), the scanner still detected -50C from N70b1...!?
Now, the case may be: when N70b1 sending no signal, the scanner will show it as -50C.
I am thinking of two possibilities, one is faulty (or dusty) n70b1, another connection problem.
So, my next step is: full cleaning of the n70b1 fan and sensor, and see if the bad ac could work again or not.
Thanks so much Cali and S-P, your posts are so wonderful.
One more update: scanned again yesterday, scanner detected -50C from N70b1 temp. sensor when nothing unplugged. Today, I take out fuse #17 from fuse box (to stop any power to the entire OCP), the scanner still detected -50C from N70b1...!?
Now, the case may be: when N70b1 sending no signal, the scanner will show it as -50C.
I am thinking of two possibilities, one is faulty (or dusty) n70b1, another connection problem.
So, my next step is: full cleaning of the n70b1 fan and sensor, and see if the bad ac could work again or not.
... this is going to be interesting if we can figure the cause of crazy A/C with a -50°C sensor.
Hope you don't pull a short straw with a bad sensor.
It could make sense the -50°C is the last value acquired - Reset the module hosting that value (OCP /HVAC) then see if that temp does refresh or not.
Is your tiny fan still spinning ?
Defective solder connection ?
Defective sensor (open thermistor)?
Last edited by CaliBenzDriver; Aug 26, 2021 at 01:12 AM.
If indeed it is just a simple thermistor as per link and the curve is known, you can buy and replace it yourself W212.
I think the entire interior temp sensors used would use the same thermistor curve/spec, for easy design of the controller board.
If indeed it is just a simple thermistor as per link and the curve is known, you can buy and replace it yourself W212.
I think the entire interior temp sensors used would use the same thermistor curve/spec, for easy design of the controller board.
What a great find Surya! The thread detail the issue of loose thermistor pins over 68 posts and pretty much guaranties a 10¢ fix without a $2k OCP replacement.
At first the sensor value is reported to be around 10K and then later 6K NTC... for these older models.
We should really find out the specific value in our W212. A wrong thermistor will simply measure the wrong temp by few degrees depending on error %.
People mention needing repeat repairs because of vibrations... I'd pin things down with a drop of quick epoxy.
Last edited by CaliBenzDriver; Aug 26, 2021 at 05:41 AM.
... this is going to be interesting if we can figure the cause of crazy A/C with a -50°C sensor.
Hope you don't pull a short straw with a bad sensor.
It could make sense the -50°C is the last value acquired - Reset the module hosting that value (OCP /HVAC) then see if that temp does refresh or not.
Is your tiny fan still spinning ?
Defective solder connection ?
Defective sensor (open thermistor)?
Hi Cali, thanks for your tips. Do you know how to reset the OCP/HVAC module? I may have a try before n70b1 cleaning. Thanks again.
Hi Cali, thanks for your tips. Do you know how to reset the OCP/HVAC module? I may have a try before n70b1 cleaning. Thanks again.
Read the post #9 above where S-P kindly took the time to research and locate the missing information to save your bacon.
Once you're done reading you'll understand this problem is a Benz stapple for nearly 20 years or since 2004.
This particular temp sensor is proven to read -50C once it goes "opened" (as in opposition to "short").
It is designed to vibrate loose from its wiring and finally you have cases where the thermistors pins just simply fall off.
THE FIX:
It really depends what stage of damage you're at!
1- either solder loose thermistor : Free
2- either replace new "8K NTC thermistor": 10¢
3- or dealer style with a new OCP : $2K
Cleaning the fan is great but it's not enough to address this thermistor failure.
You need to carefully epoxy your new parts to prevent a repeat repair.
Elephant In The Room:
The "68 post thread" shows you how mature this sensor failure really is.
Essentially this fan & sensor unit works like a baby MAF sensor for our A/C system. A stream of air blowing over a thermistor to measure a temperature.
NO DTC for MISSING HVAC Sensor... Now we know!
Other A/C temp sensors likely same deal... you must read each individual Temp sensor to validate them is now the proven procedure.
People with weird A/C acting up should consider reading all their live sensors and not expect any pointer code from our HVAC Module. The temp sensors are designed to fail silently.
The loose 10¢ part brings in $2k OCP plus the parts-darts aggravation of needlessly replacing expensive A/C parts when this is a bad old legacy money maker kept hidden by lack of DTC.
Go read your live sensors!
Last edited by CaliBenzDriver; Aug 27, 2021 at 11:47 PM.
Thanks men.... just to make sure how to deal with this little trouble senor. Is it just pry out the top ring (red in pic) and then resoldering the two points (blue arrows) with a new sensor? Any advice that I need to pay particular attention? Million thanks.
Best to inspect the thermistor first, where is the broken solder ?
If you found the broken solder only, measure the thermistor value and note down your current ambient temperature, that way it can be confirmed if it is a 10K ohm or a 6K ohm.
The meaning of 10K /6K ohm is, at 25C you will read 10K or 6K.
If the thermistor still healthy and only broken wire, just solder and dont buy new thermistor.
NOTE : The thermistor resistance can only be tested with at least 1 wire or its leg disconnected from OCP main circuits, otherwise your resistance reading will include other components.
We want to read only the thermistor resistance value.
Your thermistor set up is better than the older model cars, where the thermistor is supporting its own weight using its own 2 legs. Like below :
Cover of fan if installed
Your thermistor is on a PCB board , so aside from the 2 solder points you marked with blue arrow...from there it could be using small wires and then go to the PCB.
The broken solder points could be the small wires ....
.
Last edited by S-Prihadi; Aug 27, 2021 at 11:38 AM.
Reason: typo correction
That's a lot more robust design on the W212 for the thermistor... I'd start by measuring the resistance at those blue arrows and seeing if it corresponds to the correct ambient temp. A closer and in focus picture would help.
Evaporator 36.2C and no cooling in ac low pressure tube, problem?
Scanned agin after engine running with ac set LOW for an hour. Temp of evaporator was 36.2C. Checked by touching the ac low pressure tube, no cooling. Is 10.3bar refrigerant pressure too low?. I go crazy with my bad ac in this hot summer......: (
Please help if you have any ideas....
10bar is 145psi...
On the low side its way too high, on the high side its a bit too low.
Based on what you describe this is your suction side pressure, really close to a resting balanced pressure!!!
Cab sensors...:
What is now the cabin temp on the sensor you've just repaired? (Set to Lo it should be bypassed) and footwell, vents sensors?
Clutch fuse and control module:
Confirm your compressor spinning and the high pressure line coming out is hot (200+F) to the touch?
Is your big radiator fan spining as expected?
Bottom line:
I am guessing your compressor needs a proportioning valve replacement... not uncommon and not as expensive as a used compressor rebuilt 😏
I wonder if there is a quick trick to get the compressor limiting valve unstuck?? (like a hammer tap on a lazy starter).
Last edited by CaliBenzDriver; Aug 28, 2021 at 12:49 PM.
Thanks men!
Two points to me that I suspect the OCP temp sensor is not the root cause.
1.no cold air blowing out even when ac set as "LOW" both side (bypassed the OCP temp sensor).
2. no "cold feel" when touching on the low pressure tube of the ac system.
So will put the OCP sensor repair on my next job list.
Now, the first thing to do is to do a more systematic scanning with an infrared temp gun at several time points, such as when cold start, engine just started, and when after running for an hour (all with ac set as LOW, as well as "zone" turned off).
Will post my testing results in the thread of "ac one side cold but one side hot".
Thanks all for your wonderful help and useful advice!
10bar is 145psi...
On the low side its way too high, on the high side its a bit too low.
Based on what you describe this is your suction side pressure, really close to a resting balanced pressure!!!
Cab sensors...:
What is now the cabin temp on the sensor you've just repaired? (Set to Lo it should be bypassed) and footwell, vents sensors?
Clutch fuse and control module:
Confirm your compressor spinning and the high pressure line coming out is hot (200+F) to the touch?
Is your big radiator fan spining as expected?
Bottom line:
I am guessing your compressor needs a proportioning valve replacement... not uncommon and not as expensive as a used compressor rebuilt 😏
I wonder if there is a quick trick to get the compressor limiting valve unstuck?? (like a hammer tap on a lazy starter).
Thanks Cali, the temp readings of all sensors concerned are:
Based on the above, I think the evaporator is not as cold as it should do. So the ac system is not able to blow out any cold air to the interior.
Start with the overhead temp sensor, first. What might be interesting is to see those same HVAC parameters with defrost turned ON. That should also force the A/C on and since the cabin temp is low... it should go full blast. Having the AC run when the cabin is "-50*C" already wouldn't make sense.
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