So as you see by the title the Radiator fan is not working. My ac is fine ,Power is going to the fan and ,I hot wire the fan and it spins. I can figure out why it won't It but have to do something to do with the two other wires. Can somebody please help I can't figure it out.

 

did you check your fan relay? AC pressure switch? The fan is controlled by the ECU and based on certain parameters: engine temperature, AC available and active, etc..

You say your AC is working, how did you test that?

In general, the typical approach with these cars is to scan them for error codes.

 

No can you tell me where it is it’s a e350 2014

 

I just turned it on and it stayed on and blew cold air. Also measured the ac system pressure. The fans don’t even kick in when temps reach 85c. Can you please tell me where the AC pressure switch is and also the relay.

 

https://fuse-box.info/mercedes-benz/...uses-and-relay

Location for all fuses in the W212.. Fuse 22 in the fuse box on the left side under the hood near the windshield is for the radiator fan. Fingers crossed is just the fuse.

PLEASE be careful closing the fuse box. Otherwise, water can get in and the fan will be the least of your worries.

There is another fuse, in the prefuse box F32, named MR4 (100 Amps), it is listed at the bottom of the link. Since the AC starts, and you said there is power (12V) at the fan, that fuse should be fine.

 

No the fuse is good

 

I do not have the diagrams with me, but you will need to test continuity and voltage with a diagram. This link has a few documents of the circuits for the W212.

https://mbworld.org/forums/e-class-w...ml#post8388052

 

So I get power so it can’t be a fuse right? Unless those other two wires have something to do that?

 

Mike,

01. How good are you electrically ?
02. Do you have a bidirectional scanner which can work on MB cars ? or............do you have a friend who has a Xentry ?

Mike Wrote :
My ac is fine ,Power is going to the fan and ,I hot wire the fan and it spins. I can figure out why it won't It but have to do something to do with the two other wires. Can somebody please help I can't figure it out.

Can you explain how you "hot-wire" the fan ?

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Read here : https://www.benzworld.org/threads/w2.../#post-8900649
Download the OP pdf file.

To suit your 2014 W212 M276 3.5 NA which I am assuming is a B03 Start Stop option car, you need to substitute some information on that pdf with my writing in green , below :

9. Test of Control Signals to M4/7
The Electric Fan (M4/7) receives command pulses from the CDI Control Unit (N3/9, pin 57 petrol engine computer N3/10 pin 18, designated in WIS as ‘LUES’ and ‘PWM Signal’) via a Green/Blue wire pin 4
PWM normally stands for Pulse Width Modulation and this interpretation certainly seems to apply in this motor speed control situation.

*there are other part of the document which mentioned, CDI Control Unit (N3/9, pin 57 , you now know the correct one for your engine is N3/10 pin 18

============


This is a video of the test to see the PWM signal being read.
Do note : Multimeter using voltage scale is not accurate like a scope for PMW or Duty Cycle %, but its a good indicator of voltage climb as the PWM signal goes higher percentage.


Multimeter with DUTY CYCLE % which is PMW signal actually, is cheap now.


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01. There is no relay for the radiator fan M4/7. Inside the fan itself is the speed controller and solid state switching of big power load.

Pin 4 , small wire Green-Blue is the PMW fron N3/10 engine computer which tells the fan how fast to spin.
Pin 3 , small wire Black-Red (BKRD) in diagram but actually Brown-Red in your car is from Fuse 22 of front SAM N10/1. This I believe as low power feed for the speed controller logic board of the fan.
Pin 4, big red wire is from F32 Prefuse box. This is positive. Main power for the big motor of the fan.
Pin 4, big brown wire is from ground point W9. This is negative/ground. Main power for the big motor of the fan.


Above wiring diagram is attached. 3 pdf.



WILL CONTINUE.....................

 

Hello so finally I figured it out. Not sure why but I had to hard reset the car. Via disconnecting the battery for 45sec. It some how worked I am not sure why

 

Something I find different between the C Class test pdf and the video I linked.

C Class pdf
10.1. Test 05 with Un-Plugged M4/7 Thanks to a good friend I was able measure the control signals on a “good” 2008 C220 CDI.
Much to my relief they were identical to the results obtained for my car. Ie 3Vp-p amplitude and a variable PWM duty cycle depending on demand with a period of 95ms.

This is not the case with the W212 in the video I linked. It would be 12V ( if using scope ) and 9V ish when using a multimeter.
I to never seen a 3V PMW signal on my car, its been always 12V so far. So you need to use 12V as the PWM signal.



===============


The PWM signal from ECM pin 18 is based on algorithm/program.
Our car uses a single giant fan for both engine cooling aka radiator and HVAC cooling aka condenser.
So it is not easy to troubleshoot like those older cars with 2 smaller fans where one is specific for condenser cooling only.

This means there are 2 commanders able to trigger the fan to run. One is from HVAC and one other is from Engine.
I recall that with HVAC turned on ( me at 30C ambient temperature ), the fan will spin slow but will spin. This all depends on coolant temperature too. I meant to say COLD start or whenever engine has not reached its 95C operating temperature.

ENGINE COOLING STAND ALONE
For my car and would be identical to your engine too. If I do not turn ON the HVAC, from COLD start to warm up, the fan will only turn ON at 105C coolant temp. You need OBD2 gauge or scanner to read a true coolant
temperature as the one on the instrument cluster is on purpose a white-liar and would show like 95C only at a true 105C coolant temp.

So you need to verify, why is the HVAC commander not triggering the fan ? ( assuming all parameters are met to have the fan in a must-run state )


=============================

Update from Mike :
Hello so finally I figured it out. Not sure why but I had to hard reset the car. Via disconnecting the battery for 45sec. It some how worked I am not sure why

There is probably a DTC from HVAC system which does not allow the fan to run under the HVAC command as a safety measure. This may not produce an engine check light.
Battery removal is like a soft reset.

It may come back again this NO-FAN issue when the fault parameter is met. ( assuming this is a true fault event and not a glitch )
Best you get a proper scanner to see the STORED DTC code.

The refrigerant pressure sensor is at the bottom of the condenser.


Good luck........

 

Now watch for a repeat. If there is a communication problem between the modules, it may happen again. At least you know how to reset it until you can diagnose the root cause. Have you noticed any humidity in the cabin? carpets?

Enjoy

 

After starting it today the fan did not turn on. Even after doing the battery reset. So I borrowed a OBD scanner and this is what I got. I am just really frustrated with this.

 

If you have not already done so pull prefuse box to use same method (GLK350 shown) to test f154-MR4 (100A) continuity. May be intermittent problem. If fine, do not rule out internal problem in fan requiring replacement. Before replacement I suggest someone clear stored codes & pull new using Xentry (MB diagnostics). Diagnostic fee for definitive diagnose warranted in comparison to fan replacement cost.

 

yea I have seen this vid but since it was able to turn on just before do you think it can still be a fuse?

 

Suppose fuse itself has an intermittent problem meaning to say it is beginning to, but hasn't failed yet. Relatively easy access/check/replacement before replacing fan unit. Just saying.

 

If you decide to pull the pre-fuse box out, clean you ground contacts while you are at it.

Also, check the harness is not touching any edges anywhere. Chaffed harness can create a short to ground.

 

Agree with Chief K and Juan.
Time to do CLEAN ALL CONTACTS (+) and GROUNDS.

The highest continuous amperage draw is the fan which can be 600W or 800W, 2nd is electric power steering when and if high degree movement but its not continuous.
In country like mine tropical and traffic jam worthy of making more white hair on my head , fan runs all the time because under 80KMH natural air/car velocity is not good enough.
So any wire connection to burn out first when not clean and tight, would be the fan and next is alternator positive wire.

 

So I am a bit confused Would it not work if the pressure sensor is bad. So If it’s bad and I am not using ac but temps are at operating temp. Would it work? Or do the pressure sensor need to be good two even tho I am not using ac?

 

As explained. The cooling fan has 2 bosses. 1 is engine computer and the other is HVAC computer.
Assuming your refrigerant sensor is bad, your fan will keep on working for ENGINE, but HVAC computer won't allow your HVAC compressor to operate or command the fan specific to HVAC need.

However, your DTC is specific to the fan. So your fan is now the problem one to verify/fix.

 

so I got a OBD 2 and got the real engine temp is 105 when the fans turn on. And on the gauge it is only showing 95. So when I turn in the ac this makes me think that it could be only the ac problem maybe pressure sensor I am it sure

 

Can we get some back story first ? :

The 1st time you suspected your fan has a problem , what was the actual reason for you to start messing with the big 4 pin connector of the fan ?

You said in post #4 :
I just turned it on and it stayed on and blew cold air. Also measured the ac system pressure. The fans don’t even kick in when temps reach 85c. Can you please tell me where the AC pressure switch is and also the relay.

I do not know your ambient temperature, anything HVAC related to my experience of fan will spin slowly when I turn ON the HVAC is based on my 30C ambient temperature.

If your car engine is idling, car is stationary and you are able to get cold air from the vent at all times when your HVAC is turned ON, it does not matter if the fan is spinning or not, because the algorithm may not wants to spin the fan
if your ambient temperature is deemed cool enough for condenser to work its heat exchange. If HVAC works, leave it alone.

Your stored DTC on post #13 is probably from the act of you unplugging your fan connector, it may not an earlier DTC. Becareful with our car, everything is monitored in real time and unplugging most connector may trigger DTC.

I worry that you may not be familiar with your W212 HVAC operational logic for its fan and compressor actuation and you made assumption it is not in good working order because your understanding of HVAC in your
previous car is not the same as your W212 and you start to worry something is wrong.


I give you an example.
01. If I did not tell you that our/my W212 , if from a COLD start, will only turn on the fan when true coolant temp is at 105C, you would assume that this is a fault.....when and if we are used to older cars where coolant temp is
maintained at no hotter than 90C.

02. That the instrument cluster coolant gauge is on purpose a white-liar because MB wants engine to run hot for fuel efficiency sake without us being worried.
So, our W212 true operating coolant temp of 100 - 103C when and if the engine computer want it to be................... is hidden visually and all you see is 95C at best.

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So explain clearly the why you started this troubleshooting ?

 

ok so i starting troubleshooting shooting this because the fan didn’t kick in when I turned the ac on. Which made me research because my other cars did turn their fans on right way when I turn the ac on. And one thing let to another And was told the ambient running temp for fans was 85-90. So when I looked at the gauge in the car the fan was not spinning. So this all together made me start looking into this. Until you said to use a obd reader to get the true temp. So let me know the fans are supposed to kick in when I turn the ac on correct? That’s what I was told

 

Ok, that is good information.

Try this :
01. Set your HVAC to lowest temperature and blower to maximum speed. Blower maximum speed usually will bypass certain protocol, example smart charging will stop and do normal charging...hopefully it may do the same with your HVAC.
You need to run the engine 25 minutes for this test, to heat soak the whole engine bay components.
With my ambient temp of 30C, 25 minutes is good enough and I do some revving to 4,000 RPM to heat up the engine even more to 105C true coolant temp.


HVAC Operational Logic
Remember that the end goal for us is to see a positive result and not how the process to achieve the positive result.
If you HVAC will run cold at car being stationary and your engine does not overheat, that is all you need to know.

Don't read too much on the internet.
W212 is rather complex in its overall HVAC operational logic aka algorithm.
If your car is a variable displacement compressor, it is even more complex than the normal ON-OFF type compressor.
Don't even think of profiling refrigerant pressure the old fashion way, when you are testing a variable displacement compressor, it is a different beast and it has its own pressure vs temperature vs yada yada base map which
we will never know.

I can't answer your question with any certainty : So let me know the fans are supposed to kick in when I turn the ac on correct?
It is all in the ambient temperature as the main "cooling" source and how the HVAC computer calculated how much heat to be removed from the condenser and if fan is needed to run or not.
If computer calculated that current ambient temperature can remove the heat enough from the condenser WITHOUT fan needed to spin, that is the computer call.
If you see a house HVAC unit, its outdoor spin very slowly and not super fast.
Again, the end goal for us is to see a positive result as in a cold HVAC system and don't worry how MB computers achieve that.

 

I forgot to add.
What is your current ambient temperature ?

Heat soak the cabin first.
Use Recycle air mode , not fresh.
Turn on HEAT maximum and warm up your cabin.
This way all the cabin temperature sensors will read hot ambient temp.
And do the :

01. Set your HVAC to lowest temperature and blower to maximum speed. Blower maximum speed usually will bypass certain protocol, example smart charging will stop and do normal charging...hopefully it may do the same with your HVAC.
You need to run the engine 25 minutes for this test, to heat soak the whole engine bay components.
With my ambient temp of 30C, 25 minutes is good enough and I do some revving to 4,000 RPM to heat up the engine even more to 105C true coolant temp.

Hopefully you can simulate a hot country and your HVAC algorithm will choose maximum cooling by then.