Strange A/C electrical problem. Help Please! :( - Mercedes-Benz Forum

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post #1 of 38 (permalink) Old 03-17-2017, 02:12 PM Thread Starter
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Date registered: Mar 2017
Vehicle: 2002 W210 T-modell, E320 CDI
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Strange A/C electrical problem. Help Please! :(

Hi. Firstly I wan't to apologize for my bad English....

I have got very annoying problem with Climatronic. Compressor turns off because of too low refrigerant fill and shows it is about 3 bar. Sometimes it show low refrigerant fill error and sometimes not. But...

- Pressure measured by manometer is about 10 bars, and there is about 900 gram of R134a (checked by A/C expert and it is ok in our temperatures (about 10 Celsjus) and compressor is ok
- I have replaced Climatronic panel- it didn't worked for my problem
- I replaced Refrigerant sensor B12 for new one (Denso) on the dryer- still didn't help
- Voltage btw + and - on pressure sensor is 4,95 so it is ok
- i checked main ground bolts and tehere are ok
- checked temp sensor ant it is ok too (13 kOhm resistance)
- i disassembled K40/2 relay module (upside down and connectors are very well)
Only thing i can't do is measuring ground (car has to big resistance i think- that is why my device don't want to measure it)

I think there can be problem with Z6/16 thing which is called "Ground connector sleeve (A/C system temperature sensors)" which is showed on photo.
The problem is i can't find this thing and how it looks. Can someone tell me how it looks and where i can find it?? I don't understand what to look for. Or did someone else have common problem?

My MB is

210 T modell, 320 CDI, elegance, 2002
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post #2 of 38 (permalink) Old 03-17-2017, 02:51 PM
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hello Do you know you can obtain the sensor data and the error codes from the hidden climate control menus ?

I assume you have the same N22 module that we have for your car ( with LCD display, dual control for temeparture, REST button, etc.)

While the engine and /c running keep pressing the REST button till the menu comes up and keep pressing the AUTO button on the left to advance sensor readings, and post here. You will be able to read the refrigerant pressure value as read by the climate control (item 7) along with the other sensors. Just note them and post these values here. If the B12 sensor cannot be read, the system will generate an error (which is another menu).

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post #3 of 38 (permalink) Old 03-17-2017, 03:26 PM Thread Starter
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I know that- thank you :-) . That's why i wrote that A/C shows 3 bar while manometer about 10. I have no fault codes.

Moreover when i do electrical fan test (both auto press) and i observe no 7 value - it changes from 3 to 20. When i turn off fans- it changes back to 3.
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post #4 of 38 (permalink) Old 03-17-2017, 03:47 PM
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It would be a good idea for you to post the requested information, so we stop guessing

The refrigerant temp sensor , emission sensor, and the refrigerant pressure sensor share the same electronic ground. If there is a ground issue, the values from these sensors also would be wrong, no ?

Read these sensors and if they are within reality (the refrigerant temp about the same as outside temperature after the car sits for a while, and the compressor not running), then the ground is fine.
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post #5 of 38 (permalink) Old 03-17-2017, 03:54 PM Thread Starter
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Ok i will collect data and send it . They have common ground? So can you explain me what technically is this thing Z6/16 which is red on my diagram? I thought that is B12 ground.
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post #6 of 38 (permalink) Old 03-17-2017, 04:06 PM
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Look at the connections to the same line inside the K40/2. If you follow the line you will see it goes to the emission sensor and the refrigerant temp sensor.

The sleeve is likely the shield of the cable which is connected to electronic ground from the climate control unit.
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post #7 of 38 (permalink) Old 03-18-2017, 02:22 AM Thread Starter
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Here are the data (all in Celsius and bar).
1=11
2=14
3=04
4=04
5=03
6=37
7=03 !!! (But pressure on high pres. site measured with manometer is about 8 bar on cold engine (900gram of r134a))
8=18 (i checked resistance - about 13,8 kOhm)
11=0,5

Measured after 5 minutes of engine working.

On the whole diagram I can see that Z6/16 is place where ground splits to B12 sensor, in-car tem sensor, heater core temp sensor, evap temp sensor and sun sensor. Is it possible that grounding is ok but something is wrong with connection/soldering of B12 ground in this point?
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post #8 of 38 (permalink) Old 03-18-2017, 07:08 AM
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With connector connected, ignition on measure voltage at pin 1 of B12. Needs to be 0V, pin 3 5V reference voltage. Pin 2 varies with pressure.

Splice Z6/16 is at the base of the windshield behind instrument cluster.
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post #9 of 38 (permalink) Old 03-18-2017, 07:16 AM
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Well, the sensor values for inside / outside / heater-left / heater-right / evaporator and coolant (assuming that you just started a cold engine) seem to be plausible (which you can verify). What is not realistic is the refrigerant temperature of 18 degrees C. when the compressor is running at the ambient of 14 degrees C.

Assuming that at this point the a/c works, the refrigerant temperature should be much higher than 18 degrees C. You may have a bad refrigerant temp sensor which is a common issue when you have moisture in the system. The moisture could have been introduced when you changed the receiver/dryer and the pressure sensor. It should have been properly evacuated by a vacuum pump for some time prior to a re-fill.

You can override the refrigerant temp / fill sensor related issues to check the system through the hidden menu.

Also you said you replaced the climate control unit. Have you checked if the unit is properly version coded to match your system ?
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post #10 of 38 (permalink) Old 03-18-2017, 08:43 AM
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When Marcin has outside gauge showing 10 bars pressure and car sensors reads 3 bars, that is clear for me the car sensor is bad.
I would verify it with 2nd outside gauge just to make sure.

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