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AC only works when cold - code P261115

E-Class (W212) 2010-present: E 350, E 550

AC only works when cold - code P261115

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Old 06-13-2018, 12:43 PM
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AC only works when cold - code P261115

Hi all,

Recently acquired a W212 E63 and the A/C is only working while the engine/car is cold.

Here is the scenario:
- when I first start car in the morning, the A/C will blow cold for about 5-20 minutes of driving
- duration is shorter if the outside ambient is higher, say if it was 28c, it might only work for 5 minutes, but if it was 20c it might work for 15 minutes
- after a certain duration, the AC light will turn off by itself, and when I try it turn it back on, the AC light will immediately blink 3 times showing an error.
- if I shut off and restart the car immediately, I can turn on the A/C and the light will stay on for about 10 seconds, then it will trip off again, if I try to press it again, it will blink 3 times.
- after I park it for a few hours and the car has cooled down, it will return to the cold start scenario where the A/C will work for a duration of time.

The first try was to check the refrigerant levels, mechanic evacuated system and there was the factory specified amount of refrigerant inside system and a leak test was done and everything was fine. However the error remains,

Pulled the code, and the reader shows:
"P261115 - The regulating valve for climate control has a malfunction, there is a short circuit to positive or an open circuit (current and stored)"

My mechanic suspects that this regulating valve was shorting out when the temperature was hot. The official way is to replace the compressor as the "regulating valve" is an integral part of the Denso 6SEU16C compressor. However, I found the solenoid valve itself for the 6SEU16C compressor on eBay for about 40$ we evacuated the system again and replaced the solenoid valve on the A/C compressor and recharged the system.

It did not solve the problem and the symptoms are exactly the same as before. Ac blows cold for a while, and then trips off.

Since I have replaced the valve and made no difference, I am wondering if my mechanic has proposed the wrong solution, is the "regulating valve for climate control" really the solenoid valve on the compressor? Or is there other regulating valve I'm not aware of and we are just barking up the wrong tree and replaced the wrong valve?

Thanks in advance.
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Old 06-13-2018, 12:56 PM
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The Heater Core Valve on the W211 was a big problem for many, including myself. It caused the AC to blow warm air after operating for a short period. It would work again after cool down as you have indicated.
It is a regulating valve and perhaps this is the valve giving you the trouble code.
see more:

https://mbworld.org/forums/e-class-w...rol-valve.html
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Old 06-13-2018, 01:47 PM
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Thanks for your help. I owned a W211 before as well and I'm familiar with the duo valve.

However, when I checked the parts catalog in the W212 I'm not able to find a similar duo valve anymore. I wonder if they have used a different control for the W212 HVAC system that got rid of this control valve.
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Old 06-13-2018, 01:59 PM
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That is certainly possible, but I don't know how the system would operate without a regulating valve controlling the flow of coolant. This descriptor "there is a short circuit to positive or an open circuit" in the fault code was my issue. That Heater Core Valve is controlled by the front S.A.M. and I had a bad S.A.M. that was not signaling the Heater Core Valve to open or close properly. The S.A.M. needed to be replaced for $1,000. I hope you can get this sorted.
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Old 06-14-2018, 04:40 PM
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Key08, thanks for your help and I'm afraid you are correct that it might be the SAM module, even though for W212 its no longer controlling the duo valve. The W212 now uses an electric heater circulation pump to control the amount of heat. The SAM controls both the heater pump and the AC compressor regulating valve.

Me and my mechanic spent some more time troubleshooting yesterday and hooked up the scan tool to monitor the front SAM module signals.

When the car first turns on and AC is turned on, approx. 0.8A is applied to the AC regulating valve and the AC works fine. And the status of the compressor is set to "ON" on the SAM module. As long as I keep the temperature in "Low" and the Ac compressor cooling has constantly shown as "ON", the AC seems to work fine.

However, once I set the temperature to a higher temp, say 22c, the compressor will cycle off when cooling isn't required. And when I set the temp to a lower setpoint, the SAM module tries to turns the compressor status to "ON", however the amp draw remains to be "0 Amps" in the display data. Then instantly it will switch off again, and on again. It tries to turn "ON" but since there is no amp draw, it turns off again. It tries this for about 10 seconds, and its unsuccessful in turning on the AC compressor, so it trips off the AC and the AC will blink 3 times as I try to turn it back on. It will now show the code "Regulating valve for AC is open or short circuit"

I then turned off the car, and instantly turn it back on, and tried to turn on AC again, it attempts to turn "ON" the AC compressor without success and trips off again.

The next try, I waited only around 3 minutes to restart the car, everything was still up to temp, and this time the Ac compressor kicked on again, as long as i kept it in "low" setting, the compressor stays on. This confirms that the Ac regulating valve was NOT the culprit as being too hot and short circuited. Everything was still very hot in the engine bay, and as long as i kept it in "Low" temp setting, the AC continued operating without issues.

We concluded it was something to do electrical controls. The AC regulating valve is directly controlled by the front SAM.

So I thought maybe I would try my luck with the relays on the SAM. I removed and replaced a couple of grey relays in the SAM module and the AC suddenly worked as intended! I was very happy but it was short lived, only lasted for about 20minutes before the AC compressor wouldn't turn on again.

I then went online to Google if others have similar issue with the W212. I found that the guys with SLK seem to have a similar issue and its apparently very common for them. See thread below. I'm now asking the dealer how much a SAM module replacement is, and may try the DIY repair below if the replacement cost is too high.

http://www.slkworld.com/slk-r171-cla...d-bad-sam.html
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Old 06-14-2018, 05:36 PM
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Keith nailed another one.

Good troubleshooting btw
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Old 06-14-2018, 06:15 PM
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Ha, Fisch! Not nailed yet, but these SAMís can cause all kinds of grief. Your write up will definitely help others looking for a solution and thank you for sharing the process. You are on the right track for sure.
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