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2002 LWB LHD G400 CDI
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149 Posts
Discussion Starter #1
Hi,

I am having this problem for over a year now and will be glad to have some help :)

the car - G400 CDI 2002 LWB.
the problem - A/C stops cooloing once in a while (more ofter on days over 30^C). the timing it stops has no logic at all, can be while crusing on highway,while standing, at stops, high RPM, idle RPM, etc..
when the A/C stops it will get back to itself after random time (usually 10-30 mins or after a long rest).

to overcome it, I unplug the coolant temp sensor, therefore the system goes to "emergency mode", the fan spins at highest speed and my A/C is working perfect with no stops at all even at ambient 37^C..

I replaced the dryer, and washed the A/C system, vaccum and refilled with new gas.

I suspect one of two:
1. the fan control module might be defective as I only see it spin at lowest speed at all time (except if I unplug the coolant temp sensor).
2. the A/C pressure sensor next to the dryer, as I assume it should spped-up the fan when pressure getting high, and since it doesnt, the system pressure raise and something block it, till it rest enough and get back to normal (but I might be over imagining here: )

Anyhow, I will be glad to have your opinion about it,

thx
 

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2002 LWB LHD G400 CDI
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149 Posts
Discussion Starter #3
Hi ikeakayke,

thx for your help :)

since when the problem occour the A/C can still blow air I guess the problem is not with the evaporator temperature sensor as the unit is not frozen?

and the refrigerant pressure and temperature sensor seems more reasonable to me since the high speed fan keep the pressure low.

are you agree or you still think I need to replace both?

also, can I ask your help with P/N for both part? :thumbsup:

thx
 

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2002 LWB LHD G400 CDI
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149 Posts
Discussion Starter #7
sure, as of now I am suspecting that the control module of the front fan (the huge one) is not working properly..
not sure why I get this feeling.
So I am looking a way to see if the fan is acctually working properly as I never saw it spin more than the slowest spped (if I remember correctly you told me once it has 8 speeds..)

I thought to have another coolant temp sensor connected to the wire and put it into boiled water.. (or to try to test the speeds with a diagnostic computer).
this will help me verify if the fan or the A/C temp sensor is bad and save all the work with the A/C replacement..

thx
 

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2001 G400CDI
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322 Posts
You need DAS with which you can test each speed of the fan, but I fail to understand what the coolant temp has to do with A/C. The fan speed should be triggered by coolant temp, or A/C fluid temp, or transmission oil temp, or intercooler coolant temp and probably some more other. So the fan should respond if any of the above sensors indicates something needs to be cooled which means the module could be partially emprically tested by triggering any of the above sensors.

The fan has some big red wires leading to it right at the socket which develop cracks due to heat and the insulator peels off. I think that any humidity in there might cause the fan module to enter some protection state. Check that also.
 

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2002 LWB LHD G400 CDI
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149 Posts
Discussion Starter #9
I thought that if I can make the coolant temp sensor to read hot temp it will drive the fan faster...
you think it will not work?
Will look into the wires issue later today :)
 

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G270cdi 2004
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130 Posts
Hi, does 400cdi have two electrical fans at the front of radiators? I need some thougths about my problem, left of these seems not work (fuse is ok). I dont have A/C problems.
Thanks
 

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2002 LWB LHD G400 CDI
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149 Posts
Discussion Starter #13
Does anyone know which oem testing computer can test the front fan speed?
(IE carman or other company)?
 

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04G55AMG,08R320CDI
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371 Posts
My AC was not working very well in the hot Houston summers when at slow speed or idle. Once back to 40+ mph worked fine. Turned out the bearings in my rad fan were shot, thing ran all the time and make a huge racket. New one installed about 8 months ago and everything is now working ice cold even in stop and go freeway driving. Also had the water pump replaced 4 months ago. Not sure if that had anything to do with the issues.

Is your AC good at speed or when stopped? May help the diagnosis.
 

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2002 LWB LHD G400 CDI
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149 Posts
Discussion Starter #15
Hi Swizzles,
My A/C works fine and when I stop the car the problem appear (AC not working for few minutes or hours, that get back to itself).

The front radiator fan is working once in a while but only at slow speed and it is real quite.
So I suspect not that the electronics of the fan is broken and cant run the fan at higher speed OR the pressure sensor of the AC system is broken and therefore do not run the fan at higher speed when the pressure raise (ie I stop the car and the wind in front of the AC radiator is gone)..
 

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04G55AMG,08R320CDI
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371 Posts
I would agree perhaps it's time for professional help. Dealer replaced L/Side Aux fan 001-500-15-93 (blower) $570, 642-070-16-81 (line) $31 and $520 in Labor charges!

Good Luck.
 

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2002 LWB LHD G400 CDI
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149 Posts
Discussion Starter #17
- My car only has one major fan (no aux fans).
- There are only 2 vehicles (G400) like mine in my country and in most cases MB official workshop do more damage or ask me to ask here about the problems :)
 

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2001 G400CDI
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322 Posts
Here's one simple test that you could do so that it would simply eliminate the fan speed issue or confirm it. When the A/C is not blowing cool enough air when idle try to cool the radiator with cold water from a hose. If the air in the cabin immediately cools than the fan indeed is not doing its job (along with all that this could imply like sensors, control modules, etc.)
 

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2002 LWB LHD G400 CDI
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Discussion Starter #19
hi ikeakayke,
I did that :)
the problem is the when the pressure of the AC is high, even if the radiator cools down the system still take time to get back to work.
 

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2001 G400CDI
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322 Posts
So the fan has nothing to do with your problem. That's ok.
I think that maybe the accessory belt or the A/C compressor 'flywheel' is covered in oil or lots of dirt. That would make your A/C spin at much lower rpm or not speen at all until something like heat or inertia clears the area a little. Did you check that?
 
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