My climate control works fine in the winter, and when the temperature outside is above around 70 degrees. When it gets warmer, after the car has been running for a short time, the ventilation (air ducting) that normally comes out of the center nozzle switches to below and defrost. Even if I adjust the temperature settings on both right and left to lowest temperature, nothing changes.

When this happens, the normal manual control that I have over the air ducting using the knob on the Pushbutton Control Module (to make it come out above, below, side, defrost) quits working.

Another observation when the Climate control quits working is that the red LED that normally is extremely bright on the center nozzle quits working correctly. Normally, this LED is bright, and goes off as you move the dialer on the center nozzle to a scrolled down position. When the above happens, it now goes to a dim red, and stays that way.

Lastly, if it cools down outside, it will begin working correctly again without a reset.

What I have done so far:

I have a new evaporator temporature sensor.
I have a new Climate Pushbutton control module.

I suspect that it is a "sun sensor" but the Mercedes Benz service manual gives the impression that it would only have a slight effect on the Climate control, making small adjustments in the temperature of the air coming out, and not control of the stepper motors or air ducting (even though it controls the temperature by adjusting a stepper motor for mix of warm air with refrigerated air).

I don't suspect that it is a stepper motor since it doesn't happen to an individual duct, it happens to both sides at the same time.

If I catch it working correctly, I can disconnect the incremental adjustment motor electronic control module in the dash and lock it in the position for A/C, but I would like to fix it for good.

Any ideas?

 

is like sun sensor , or outside temperature sensor..

 

I went ahead and disconnected the sun sensor. It was an amazingly easy job to do, and everything thing began working for me.

NOTE: Even the Mercedes Tech didn't believe that the Sun Sensor could have as much control over the vents as it did.

It can completely shut them down.

 

Could you tell me where sun sensor is located, Thanks M

 

After having a problem with my A/C for two years, and blowing more than $2,0000.00 with the Mercedes Benz Dealersihp to fix it, only to figure it out on my own, I thought I would update everyone with the hope that it can help others.

I finally received my new "Sun Sensor" today, and installed it. I have been using the car for the past 4 days with the old Sun Sensor disconnected. The climate control seemed to work perfectly. After using it with the "Sun Sensor" for one day, I can't tell a difference.

If you ever have a problem with your Climate control ventilation, and it doesn't happen to only one side of the ventilation (if it does, it is likely a stepper motor controller), then disconnect the "Sun Sensor", and go from there. It is the easiest to disconnect, and it has an incredible amount of control over your ventilation. If it goes bad, it can completely shut down your pubshbutton control module control of the ventilation. The temperature and blower function can still work, but you will not have any control of the vents.

Also, and very important when I purchased this car, the A/C never seemed quite right. I never noticed it on an average summer day, but on a hot day, it didn't seem like it worked like my 500 SEL did. The heat was always fine, but the A/C never seemed to blow correctly out of the center nozzle (vents). It still worked, and I just thought it was a poor design.

I can not believe the difference in my A/C after disconnecting the Sun Sensor. My A/C now works incredibly. It works perfectly. It cools quickly, and attenuates properly so that I do not have to adjust the temperature to stay comfortable. I can now see that the Sun Sensor was going bad, but not bad enought that it was diagnosable.

Running the diagnostic on the Pushbutton control module (pushing the REST button for 10 seconds, and then scrolling with the left climate control adjustment buttons until I reached #12 for the sun sensor) did not show a problem.

If you have any questions about the Climate Control, I would be happy to give you my opinion. I am no expert, but have been through this system from one end to another to finally find the problem with my own car. I own the Mercedes Service Manuals, and they are not very imformative. The suggestion from the Service Manual was to replace the center nozzle and/or stepper motor control module.

 

Good post.... but you might want to post a picture and explaination of how to remove the Sun Sensor.

 

Good idea! Removing the "Sun Sensor" is very, very easy.
1. Pop the hood.
2. Remove the back 5 plugged grommets that hold the insulating mat to the bottom of the hood. You don't have to do this, but it makes the job easier.
3. Remove two phillips screws at opposite ends toward the back of the vinyl cover (closest to the windshield) on the bottom back of the hood. This Vinyl cover extends the width of the hood and keeps water out the engine where the air comes in for ventilation.
4. Pinch the pinch clips that hold the vinyl cover to the bottom of the hood, and remove it.
5. You can now un-plug the Sun Sensor. It is in the middle of the hood. From the above, it looks like a black rounded knob poking through the hood. From the bottom it is an electronic component that is about 5 inches long, and 1 1/2 inches wide with wires plugged into it. It snaps out of its position, and there are no screws holding it to the hood.

Obviously, intalling it is the reverse of above.

That is it. Hope this helps you!

 

Thank you for the step by step info dcsimmons!

Isn't that sun-sensor is also used by the command system to determine whether to display the yellow (brighter) during the day OR blue (darker) during the night?
I also notice the instrument cluster is brighter & more contrast during the day.

Hows the behavior of color/brightness adjustment while having the sun-sensor disconnected?

I may have similar problem with opposite systomp. In the winter, heater works fine then 20 mins later the outside cool air is also blown strong via center ventilation

 

I am sorry, I just noticed this reply from a couple of weeks ago.

It is very possible that you are right with the "color/brightness", etc. issues. If I had paid attention to it when the Sun Sensor wasn't installed, I could have easily verified it.

If I notice anything I will report back.

 

Update after using "Sun Sensor" for a while!

Now that I do have a new Sun Sensor, I can tell the difference it makes, it is small, but signficant (if that makes any sense). You will notice the more cooler air coming out of a vent in the front side if the sun is shining on that side, and it does assist in keeping me comfortable. I have yet to change my temperature to be comfortable after installing the new Sun Sensor.

Also, now that I have done some more experimentation, I could have really quickly diagnosed the problem.

Entering the A/C diagnostic mode (pushing on REST for 8 - 10 seconds with the A/C on, and then using the drivers up and down button to scroll) and scrolling to #12 you will see a percentage displayed. If your Sun Sensor isn't working, it will either show "0%" or "error", depending on what version of software you have. My particular version showed "0%", and didn't display an error or it would have alerted me much earlier in the process that it was a problem.

After installing the Sun Sensor, and monitoring it, The % changes all of the time depending on the direction, and when it changes, you notice a corresponding change to ventilation. For example, if you are just driving down the road, it might be showing 86%, and when you go under an over pass or something that puts it in the shade, it will immediately go to 12 %, and back to 86% when you are back out again.

For your information, here is the list of information from entering diagnostic mode:

01 In-car temperature sensor.
02 Outside temperature sensor.
03 Heater core temp, left.
04 Heater core temp, right.
05 Evaporator temperature sensor.
06 Engine coolant temperature.
07 Regrigerant pressure in bar (e.g. '4' is 4 bar).
08 Refrigerant temperature.
09 Not used.
10 Heater blower control voltage (normal 08-6.0, meaning .8 to 6 volts).
11 Emissions sensor voltage (to detect atmospheric gases and recirculate interior air).
12 Sun sensor voltage (to shift airflow in car).
20 Control current for auxilliary fan (electric fan on radiator, given in milliamps or mA).
21 Engine speed (x100).
22 Road speed (km/h or mph depending on installation).
23 Battery voltage at terminal 58d (as a percentage of total voltage, e.g. 99.0 = 99%).
24 Battery voltage (e.g. 12.8 = 12.8V).
40 Climate control software version.
41 Climate control hardware version


Please give credit to KENSTUDIOS for the above. This information is invaluable, and I printed it up and keep it in the car for reference. It is really informative.

For example, since you can compare the temperature difference of the inside, outside, both sides of th heater core, evaporator core, refrigerant temperature, and refrigerant pressure, you can quickly diagnose a problem.

Hope this helps!

 

How do you get out of AC diagnostic mode?

 

Push the "REST" button again.

 

This is very interesting and valuable information! I have noticed that my climate works ok for a while in the warmer days but then all the sudden warm air starts coming out of my drivers side vent. For the past couple of summers I had just turned off that vent. I think now I am going to take a look at this sun sensor. Could you let me know what they cost maybe? Thanks again for all your help and time to describe your situation to help your fellow Mercedes enthusiasts.
Johan

 

If I fully understand you, that by "drivers side vent" you mean not just the vent on the side by the door, but the vents on the "drivers" side, then I dont' think it is a sun sensor in your case. The Sun Sensor is arount $125.00.

If everything is working correctly out of the center nozzle, and on the passenger side, and you are actually getting warm air out of the driver side (not just less cool air), then I actualy think your problem is the stepper motor that controls the flap that distributes the air from either the evaporator core or the heater core. If cool air is coming out of the passenger side, then it looks like the warm air is the result of the stepper motor on the drivers side set to a wrong position and running the air through the heater core and not the evaporator core. There are two different stepper motors to control the air separate from the left from the right, and it appears as though the one on the right is working, and the one on the left isn't after it heats up, or shorts out.

Of course, the Pushbutton Control module could be sending the wrong information, but I think it is unlikely. Also, the Actuator (stepper motor) contol module is such a discrete logic system that I can't see heat impacting it. I took mine apart to see how it was made, and I can't see them ever going wrong.

Something else you might check is whether or not your hose that drains condensation out of the evaporator core tray is plugged up. It is very likely that what is happening is that after running the car for a while, the condensation (water) is building up and shorting the stepper motor.

Depending on what year your car is, some of the stepper motors were bad in the earlier years, but their symptoms would have been more inconsistent and yours seems to be predictable. By that I mean that you know that after your car warms up warm air is going to come out.

What I would recommend you do to verify your Sun Sensor is ok is enter the diagnostic mode on the pushbuton control module and scroll to step 12. Drive the car around with the A/C on and watch the numbers change as you go in and out of a shady spot. If the numbers are changing, then you are ok.

Good luck, and I hope this helps!

 

Well I have watching this sun sensor very closely lately since you posted this. Today my sensor went all over the place from 0% all the way up to 122%! So is it possible for it to go so high or has it gone crazy?
Johan

 

I haven't seen mine go above 100%, but will pay more attention to it. A good way to see if it is stable or not is to sit in the sun, and watch it. It shouldn't change at all (unless the shade changes). Then sit in a shady spot, and see if it changes as well just sitting there. If it is constantly moving even when you aren't moving, then it is bad. If it isn't then there could still be something wrong with it, but I would kind of doubt it.

Good luck!

 

Well I think I answered my own question today. On my way to work the sun sensor read 14% in the direct sun and in the shade and never changed for over an hour. I think it is messed up for sure now.
Johan

 

Something that you might also want to keep in mind is that if the sunsor is ever painted, it will show faulty. If you have had your hood painted, unless the painter knew what it was, they probably painted over it.

Just a thought!

 

THANK YOU!! for sharing such a comprehensive and effective diagnostic info!

It has been so frustrating trying to reproduce this issue to SA @ the dealer as he kept telling me that it is normal. Especially when we tried to reproduce the issue, we just let the heather running with the car sitting in the parking lot, hence even the air duct was opened by faulty sun-sensor, still there is no cool air blown in. CanNOT reproduce, finally I gave up and just turn on the re-circulate air cabin (no outrside air in) whenever it act up. … sorry to digress.

I will enable the diagnostic mode to determine if faulty sun-sensor is the cause with my problem. I hope this is it.

Thanks again for the detail valuable info dcsimmons You da man!


.

 

I have 2001 CLK 430 (W208), I took to this AC shop, the guy told me that I have to replace the Climate Controller , and it will cost me $1000

I have the "EC" light always Orange, so they way to go around, is I have to start the car, then turn on the AC, then turn off the engine, press the "EC" button, light goes OFF, and when I start the Engine, the light stays OFF>

After I read this post , I though it is probably from that sun sensor, but I open up the hood, and took off that cover, I couldn't see any sensor there.

Can you guys help me out here, your opinion, if you ever heard about that problem with "EC" light to be ON


Thank you

 

Your issue doesn't sound like a sun sensor. There is a possiblity that you are low on freon, and so when the car first starts, the pressure isn't sufficient enough that the low pressure valve (usually on top of the Dryer) kicks in. If this happens, it will kick off the compressor. If the compressor kicks off, and you are in A/C mode, there is a possiblity that it will kick to the economy mode (EC).

A possible reason that it stays off while using your approach is that when you turn it on manually, it forces the compressor to run for a period of time long enough to have enough pressure to keep the low pressure sensor from kicking in, especially if you are driving down the road at higher rpm.

If this is the case, you pressure is right at the threshold level of the sensor, and so adding freon would possibly eliminate the problem (assuming the sensor is not faulty).

Of course, if your air is cold as it should be, you aren't likely low on freon.

 

I had the same issue, had the whole thing checked out , thanks to you guys on this forums, i was able to check thru the ac setting and check whats wrong with and found out the overhead control is bad, that has a sensor by the sunroof button switch, is bad it was telling the car, the inside temp is 0 celcius so was making the car blow hot air, only way to get cold ac air was to go down to 54 degrees setting. so gotta order that part and instal do i need to program it with the STAR system after i install it my self or no need to reprogram just plug and play ?
Thanks guys!!

 

I am sure it is plug and play, and if I recall correctly, calibrating the slider knobs (making sure that 71 degrees is in the center of the knob between the blue and red lines) is a manual thing and not done with the star system. I think it is a mechanical slider adjustment on the side of the slider knobs for calibration, but I could be confusing this with one of the other MBZ's I have had. I no longer have the S430 or would check it and see for you.

Hope this helps

 

Thank you so much for your post, even a independent MB Shop couldn"t find the problem said it was normal for the car , and when i entered diagnostic mode it showed the car was reading it was 0 celius inside the car and thats why car was blowing hot hair in auto mode and found out the problem was the over head control that has the sensors reading inside temp. so going to order it and have it replaced.
Thnak you!!!

 

I have another problem. When i switch both sides to "LO" there is a big differance of temperature of +/- 5 degrees Celsius. It looks like there is no AIRCO in the air on the left side, it's a bit cold but not really cold.

So i was checking my sun sensor and thats acting a bit weird. It's between 0 - 39 %. It looks like it doens't work on the left side. When i'm driving with the sun on the left side, it shows 0%. When the sun is on the right side it's 39%.

I disconnected the sun sensor but there is no differance as before. Still big temperature differances between left and right. It's not only different in the middele console vents, it's all over the car.

I've been checking all the sensors and here is the list (the list when you press REST for 10 secs):

00: +20,6 C
01: +20,0 C
02: +49 C
03: +15 C
04: - 12 - +36 C (BROKERN???) (SECOND CHECK: +8C)
05: +12,1 C
06: +86 C
07: 6,5 BAR
08: 29,6 C
09: 0,0 K (0,2K)
10: 1,7 V
11: 0%
12: 0%
13: 0%
14: 0%
15: 0%
16: 66 - 110 (BROKEN???)
17: 913
18: 19,5 C
20: 40%
21: 649/MIN
22: 0KM/H
23: 44%
24: 14,2 V
27: 100%
28: 0%
29: 100%
40: ZU
41: ZU
42: ZU
43: ZU
44: AUF
45: AUF
46: ZU
47: ZU
48: UMLUFT
49: AUS
50: 27
51: 4198
54: 36
55: 10
56: 28
57: 10
58: 41
59: 02
60: 22
61: 13
70: AKTIV
71: AKTIV
72: INAKTIV
73: AKTIV
74: GERENELL
75: INAKTIV
76: ZEITBGR.
77: AUTOMAT.
80: AUTOMAT.
83: MÖGLICH
84: m.Sonne
85: AUTOMAT.
86: GESCHL.
87: ESL
96: 24 Nm
97: 70%
98: 700 mA
99: 18,9 C

Can anybody help me??? I think it's weird sensor nr 04 is fluctuation so much, right?

Does anybody knows where all the nrs stand for? I found out a few, but most of the list go to sensor nr 49. Anybody got a complete list?

Thanks,

Bori$