75gasgas

Hey there,

My 2011 E550 4matic with 156K on the odometer needs a little help.

The issue I am having is with the radiator fan. With the high temperature we have been experiencing, I was parked for about 15-20 minutes with the AC running waiting on an errand. It was very hot and humid that day literally 101degrees on the thermometer. As I pulled in the garage I heard the fan on and running very loudly. Not out of the ordinary given the heat and the drive.

I started the car this morning and I could hear the fan but within a minute or so it accelerates up to warp speed and stays there. I have searched this and other forums and found the post about the AC refrigerant pressure being too high in the system causing the fan to do this, I read the live stream data and it read 28bar. I tried letting some refrigerant out and no change to the fan speed. I rechecked the refrigerant level and added back was released. The gauge on the can reads in the "green" given an ambient temperature of 78degrees which it was at the time of filling. The AC blows cool.

I tried just disconnecting the battery in hopes that a reset would trigger the fan to go back to normal. No luck.

I inspected the AC pressure sensor and it looked in good shape and the wires look undisturbed.

There must be a cooling fan motor relay somewhere. Does anybody know the location of it? Or part Number? I have heard this fail on other makes and models and cause the fan to run at warp speed. I'm not sure if the same applies to my car though.

Thanks in advance fo any help !!
Brad

KEY08

https://mbworld.org/forums/mbworld.o...d.php?t=707835

there are many threads about high fan speed across all MB models.

MBENZTECH

First of all, if you suspect the fan is going full blast due to high pressure in the A/C system then all you have to do is turn the A/C off. With A/C system off there is no request for fan activation. Second, if the fan is going full blast with the A/C off and the engine cold...... Then I am 100% sure it is your engine control module. I have replaced many, many of these modules for the same symptom you are having. Of course, the right thing to do is to take it to a shop with the knowledge to test the signals coming from the Engine module and going to the fan.

75gasgas

Thanks for the help. I called the dealer and the earliest they could get me in was July 30th. I'll update after then.

When the ECM turns out to be the problem, am I best off having the dealer address this? Any chance you have a ballpark estimate?

Thanks again!

Sunnyslope48

Spend some time on Youtube seeing if there isn't someone who has posted information about this problem. I'm pretty sure I have seen a few videos about this within the last couple of weeks.

Arrie

Pressure reading at 28 bar sounds high for me. I have looked my live data and I remember seeing 13 or so bars...but I can re-check again.

Pressure sensor looking ok outside does not mean it is ok inside. Perhaps it is this same sensor reading 28 bars that to me sounds high.

Fan regulator may be built-in the fan itself so if that goes bad then it takes changing out the whole fan.

Arrie

Quoting my own post:

I checked the refrigerant pressure in my 2013 S550 and it reads between 13 - 14 bar (like I remembered from my 2010 E550). I did get it up to 16 bar when I turned the A/C compressor OFF for a few minutes and then turned it back ON, but it quickly came down to around 13.5 bar again. It understandably fluctuates a little bit as it runs but stayed below 14 bar. Outside temperature reading 99F.

If your system reads 28 bars you either have a malfunctioning pressure sensor, you have added way too much refrigerant in the system or you have plugged piping. I understand the problem started before you touched the refrigerant so it now points to faulty pressure sensor or plugged pipe.

Plugged pipe is not very likely but there is a thing called "Orifice Tube". This tube has a screen mesh before the orifice where the cooling action actually happens, i.e. the liquid form refrigerant flows thru it and expands behind the orifice to gas, which creates the cooling effect. If the screen mesh (or orifice) plugs up it certainly will increase the pressure in the system after the compressor.

I'm not sure where the orifice tube is located in this system but I am guessing it is where the two "thick" plates meet next to the low side pressure check point. konigstiger could probably post parts diagram for this.

I don't know the cost of the pressure sensor or the orifice tube. Tubes for other cars can be bought for less than $10 but for MB it probably cost way more from the dealer. Pressure sensor would be way more expensive I guess.

If I was you I would get both these parts and change them out as changing either of them requires draining the system. I'm guessing the problem you have is with the sensor.

75gasgas

Thanks for the reply!

Yesterday I unplugged the ECM and I couldn't see any corrosion or obvious signs of trouble with the plug.

I also unplugged the fan and looked for corrosion and read the voltage from the green wire as 3.1 volts. The red/green stripe wire was constant 12v. This was as I started the car, (fan on but at warp speed) and constant 3.1v as it spooled up.

My AC is not running normal either now. It gets cool but, not cold and is at 26 bar this morning.

Thanks again for the help!

75gasgas

UPDATE:
Good morning,

I got the car back yesterday and all is good. Turns out it was the AC pressure sensor. A simple DIY job but, I couldn't bring myself to discharge the refrigerant into the atmosphere. I told the dealer to go ahead with the repair. The (bad)sensor was reading 30bar. I could confirm that with my icarsoft reader and the new sensor read 13bar. AC is blowing cold and the fan is back to normal. The bill was just over $600.

Thanks to all for the replies and suggestions!!

Arrie

Good you got it fixed. This proves that if pressure gets high (or just the reading with bad sensor) makes fan run fast. I experienced this when my pressure really was high but at the time I did not have the scanner to read how high my pressure was.