My electric fan does not seem to come on. My car is OK , is running below 100F
here in South Texas.
Do these go bad considering the age of the car, it has 178K miles.
Need to know which relay and fuse is for this electric fan and I assume
the electrical connector is on the top somewhere?
Can someone help me by looking MB manuals and posting how to test for this
and replacement of the fan.
Thks

 

The fuse for the fan is located at the positive terminal of the battery.

 

Does yours have a viscous fan behind the radiator and two electric fans in front of the condenser? If so, the fan fuse is listed on the "map" inside the under-hood fuse box, on the driver's side of the car.

 

Not on an ML 55 or 500. They have one large fan doing all the cooling and the fuse on the battery controls it.

 

how can i test this electrical fan by directly testing with 12 Volts?
I tried another relay and does not come on with a/c on
and also the 80 amp fuse is OK.
These fans are super expensive
I disconnected and taped the two connectors on this fan
and wired directly to the battery, not sure what the small black connector is on
the top of the fan. But fan does not come on.
can someone help?

 

Remove the connectors from the fan and first test if you are getting 12v at the RED wire. If so, fashion two lengths of wire that can go from the battery to the fan, the same thickness as the RED and BROWN wires.

Then run one wire from the pos. battery terminal to where the RED wire was attached to at the fan and then run the other wire from the neg. battery post to where the BROWN wire was on the fan. The fan should run.

 

I tried that Major with a thinner wire just to see if the fan comes on, but no luck.
Does it need to be the same gauge just to see for a 5 secs that the fan comes on or not?
Is there are any one who just repairs these module or do I have to buy a whole new fan, I saw an aftermarket one for like $400 on ebay

 

Are you absolutely sure that fuse on the battery is OK?

How many wires are on the fan and what color are they?

 

There are 2 wires, one red and one brown going to the fan controller. The 80amp fuse is OK. After removing the fan assembly, some of the ball bearings on the motor are missing. Also, my coolant light comes on, with no loss of coolant and reservoir (2 yr.old reservoir) being full. So, I thought it was the sensor inside the reservoir, so I replaced it with factory reservoir, and the coolant light still stays on. Wondering this light is coming on because of my fan? are they related? I ordered a new aftermarket fan, which hopefully works.

 

The coolant light is on because the fan isn't working.

 

Now that makes sense now, as I could not understand why this light was
coming on. I thought is was the sensor in the reservoir.
Waiting for the new electric fan.
Guess after 14 years, it quit.
Thks for your feedback!!

 

I replaced the electric fan in my 2000 ML55 with a DEPO brand.
It worked fine for like 2 weeks, and for the last 2 days, the A/C gets cold and then when stuck in traffic, gets warm, and see the temp climbing and A/C may start working again.
Yesterday, that car was overheating, even with A/C turned off.
and the fan was not running.
This morning with cold engine, I check all fuses, even the fan relay is new
I started the car, turned on A/C, fan turned on???
What are the sensors that turn on the fan?
Or is this a bad fan??

 

You have to change or weld the fuse at the battery connector thet attempt to go bad a lot and it also turns on the coolant light on

 

Team Forum... need some help. I have 2003 ML55. Big single radiator fan up front. The fan 'runs' but does not cool the engine on hot days. If its 90 degrees or higher outside and I leave the engine running while it sits, the temps start to move up quickly and the coolant light comes on. Once I start driving, especially on highway, the temp drops back quickly to just above the 80 mark on the temp gauge in the instrument cluster and the coolant light goes off.

I too thought for a long time that the coolant light meant that I was low of coolant. Of course that was wrong and now I have a bit of an idea what the issue is (the fan is the problem and possibly not getting a signal or something). A few years back the fan would run at super high revs and was super loud. This would happen while it was hot and just sitting idling. My guess it was doing its job then.

I checked the big 100 AMP fuse by the battery... looks good. I have checked the connections - a black wire and a brown wire. Checked the #26 relay - replaced and new, assume its good if the fan is 'running' at low speed. If the fan runs.. and the 100 AMP fuse visually looks good, we can rule that bit out right?

I have same questions as bballfreak above.. 'what sensors turn on the fan' or in my case 'what sensor tells it to kick into high gear and do more cooling'? The signal is getting to the light in the dash... just not to the fan to tell it to go faster.

Thanks for the help and any suggestions or tips.

 

Have you scanned for any saved codes?
If not scan and post here.

EDIT - not sure if this is related, however read post #4 & 5 here

 

Yes, no codes that I believe are related. I've long had an EGR code (P0400) which I believe to be a vacuum leak somewhere. Thanks for your inputs and guidance.

Thanks for those posts.. I did check them out... Also did a little testing.. I took the coolant reservoir above the engine off just enough to undo and re-attach the electrical connection there on the back/top of it. I had taken it off earlier this to research the vacuum leak. Also there are three wires going to the fan. The two main power ones and the electrical connection thing just to the right of them. I popped off that connection (I think it actually has two wires in it) while the truck was running and the fan stopped. I plugged it right back in... fan runs right away (what I would call low speed).

So I drove it around the neighborhood to get the engine and coolant to temp (this means up to the 80 mark on the gauge in the instrument cluster. ) . Pulled back into the garage and let it sit and idle expecting the temp to start to climb. It did not... Also unexpected, the air continued to blow cold. Normally when it gets 'hot' (above 90+) the air typically starts to go warm and that is my hint that uh-oh.. the temp is getting hot on the engine. So staring to get cold I turned the air off... that is when I heard the sound of the change in speed of the fan. (Hmmm) . I was able to replicate and confirm this with my wife in the car turning the air on and off.. the fan responded appropriately.

I am bit stumped... I did notice that the instrument cluster was 'solid'. What this means is that typically my over head cabin light and the instrument cluster tend to 'flicker' a bit or at a minimum have a pulse to them when just idling or sitting at light. I've replaced the voltage regulator before and thought that was the end of it. Now seems it is back. Not sure if this has anything to do with this particular issue and wanted to mention it.

Also.... I have the funky fuel gauge issue on this truck. Not too long ago I was convinced it was the fuel pump and now have a new one. The fuel gauge still does the "shows full immediately when you fill up' then not too long after... goes to zero. Again.. not sure if all these things are related or not.

Also found this thread.
https://www.benzworld.org/forums/w16...tle-hot-2.html

Still working on it - report back later as I know more. Thanks for the assist..

 

When a fan runs, but not at the speed that it should, then it is a faulty fan module. The proof of this is when you drive at hwy. speed, the onrushing air makes the temp. to go down.

The module cannot be bought separately as the whole fan must be purchased.

 

Thanks for this info, very helpful. I took the truck out driving today and not exactly sure why... but the coolant temps / engine did not start to heat up at idle after warm. It was 90 degrees here today and I'd been driving for 30 min or more when the mrs went into a store for 10 min or so. This is the time that the temp starts to creep up from 80 into the 90+ range and the A/C starts to go hot.
I intentionally let it idle in the parking lot and everything held steady. The coolant temp stayed just a tick over 80 and the air stayed cold. Wondering if my unplugging and replugging of the electrical connection on the coolant reservoir may have done something. Going to hold for now and see if the fix holds.

Thanks for the diagram and input. I think you may be right and ultimately I'll have to get a new fan. I do recall it running like a jet plane with super high speeds more than once, quite often actually, a few years back for no apparent reason. If and when the issue re appears I'll let the forum know and the ultimate outcome/fix. Thanks

 

Did you ever fix your issue? I seem to be having a similar issue. Intermittent coolant light while the level is fine, ac clutch kicking on and off, temp raising above 80 but not over 100,and the fan isn't kicking on it seems. The ac is what lead me to the issue and without the fan running the high pressure side of the Ac system keeps kicking the ac on and off.

 

Yes, the fix for me was to buy a cheap / large high amp fuse and broke it in half to use the copper. I put the pieces in under the fuse - basically reinforcing it - and have had no issues since. Must have been a contact issue. May be able to achieve the same result by giving it a good cleaning...

Hope this is helpful. I also disconnected and reconnected the various electric connections a number of times trying to diagnose... could have been that as well.

 

Apparently if I turn my AC button off and then back on the electric fan kicks on and operates as it should.