In the "B" slot there was a Blue relay, and calls for a 15 amp fuse, part # 0025420119. In the "C" slot there was a Green relay, and calls for a 30 amp fuse, part # 0015429619. The slots were marked with a white letter under the relays. They were switched and I have now put them back as you suggested. I'll replace the 15 amp with a 25 as soon as I get home. You are correct, it is a 124.131 chassis and a 606.910 engine. Thanks for the help, I'll let you know what happens.

Thanks,

B52rule

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1960 190D (college car), gone
1995 E300D, 325 k
2019 LEXUS UX 250h (spouse mobile)
2003 Nissan Frontier Crew Cab, 125K
2007 Jeep Grand Cherokee Overland 3.0L MB diesel, 200K
1978 GMC Classic Motor Home

In the "B" slot there was a Blue relay, and calls for a 15 amp fuse, part # 0025420119. In the "C" slot there was a Green relay, and calls for a 30 amp fuse, part # 0015429619. The slots were marked with a white letter under the relays. They were switched and I have now put them back as you suggested. >>


They are inter-changeable, so I see this happen quite often..
Usually happens when someone is testing relays and changes them , then forgets what goes where...
They mistakenly switch the slots... resulting in repeat fuse failure of a/c
low fan circuit/fuse.....
Recommend 20/25 A for low fan [ Benz approved this change],
as the 15 was found to be borderline on low fan circuit..
30A on coolant temp high fan.

It's all bolted up with the relays in the right places and correct amp fuses. Interesting to note, I bought this as a Starmark vehicle 1999 from one of the North County dealers here in San Diego, had it back for several issues, none of them for cooling however. When I did mention that it had these symptoms I was told it was normal operations. It has never had the A/C system worked on while I have owned it. Nothing more than routine maintenance here, oil, filters, coolant etc. I'll run it for a few days any let you know the results.

Thanks,

B52rule

__________________
1960 190D (college car), gone
1995 E300D, 325 k
2019 LEXUS UX 250h (spouse mobile)
2003 Nissan Frontier Crew Cab, 125K
2007 Jeep Grand Cherokee Overland 3.0L MB diesel, 200K
1978 GMC Classic Motor Home

Recently my '95 E320 wagon was running warmer than usual and I finally realized my low speed fans were not coming on. Thanks to this thread, I found the problem.

I've owned this car since 2001 and as far as I know, no one has worked on the a/c system during this time. But sure enough, the relays were swapped and the 15A fuse was blown. Thanks for helping me fix it!

__________________
Glen Tokuhara
Beauty & the Beast and the wagon that could!

__________________>>

Glen
Double check the relay positions b/c that old thread was incorrect on locations depending on V8 or IL-6 model.

On you chassis , the blue relay goes in slot B and is low fan, [ K10] with high fan being slot C. [K9]
So, slot C stays with a 30A fuse and slot B can be increased to 20/25 for low fan [ a/c activated]. They found the orig 15A did not hold , specially when they came out with the Dual Fans set-up.
The confusion on that old thread was we did not realize the difference in the two models [ 124.032/124.036]
It was later changed in the archieves and I edited that one for future use.
It is easy to verify the correct locations by activating the high fan by pulling the plug on the blu 2 wire sensor at the therm housing ..that defaults HIGH fan ..when that high fan comes ON , simply pull the green/30A relay from it's slot..if the fan still runs , you know you have the relays backwards [ wrong slots]...sorry for the confusion.

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A Dalton

Thanks Arthur, I'll verify tonight. Just so we're clear, this is for my '95 W124, E320 wagon...3.2 liter I6. It's a late car so has the 4-prong thermo sensor.

Yes ..the later went to the 4 prong , but that is still the same ..they just put 2 sensors into one casing , eliminatingthe 2 wire blu sensor...same deal..if you unplug that sensor with the car key On, the high fan will come on [ that is how we check high fan circuit]..when that fan is now On, it will quit when you pull the high fan relay, which should be the 30A/Green relay...if NO, the relays are in the opposite slots as they are supposed to be,and you will never know that b/c everything still works, but you will have the wrong fusing.. If the car was the V8 , the relay slots are different.
Let me know when you check it.

Another way is to jumper the sensor at the a/c drier that has the 6" pigtail wires on it..when you jumper them , the LOW fan comes ON ..you then pull the blu relay and that fan should stop if the relay is in the correct slot...either way , both test will tell the same tale and are simple , quicky tests.

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A Dalton

Ok, I finally had a few minutes to verify everything. In my '95 E320 wagon, the high speed fans are controlled by the GREEN relay with 30A fuse in slot C, which is closer to the front of the car. The low speed fans are controlled by the BLUE relay, now with a 20A fuse. This relay is in slot B, which is towards the rear in relation to the GREEN relay.

I verified the high speed relay by disconnecting the 4-prong thermo sensor which caused the fans to run at high speed, then I pulled the GREEN/30A relay and they stopped.

Thanks again for your help!

Very Good..

You're Welcome.

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A Dalton

Arthur, you must be getting pretty close to induction into the automotive Hall of Fame by now. Or is it sainthood? Something was mentioned early in this thread that I've puzzled over for a long time. Since I'm still a bit shaky on the finer points of electric circuits, help me out with this: the OP said that pulling the thermoswitch (blue CTS) to default hi fan was the result of creating infinite resistance across the sensor connector. But if that sensor is a neg temp coefficient resistor, it seems like current shouldn't flow to the hi fan until resistance goes DOWN far enough, not goes INFINITE. What (else) am I missing here?

__________________
1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't

<

Arthur, you must be getting pretty close to induction into the automotive Hall of Fame by now>

Couple of more weeks...............

The Default fan is open circuit detection by N22 module and it is an engine over-heat protection circuit so you don't blow the engine if that sensor circuit has a failure....it has nothing to do with the ohms value of that sensor..it is triggered when it it sees open circuit/failure anywhere in the temp INPUT circuit for the N22 module and that includes wiring harness, connectors, and sensor..
So , if sensor fails, wiring fails , open circuits , etc...the high fan Defaults to protect the engine in the event that system is not working at the same time an over-heat condition exist..we just use that info to trick the N22 module into thinking there is an OPEN circuit by unplugging the sensor so we can Verify the high fan circuit w/o getting out meters and schematics, etc. It is just another Trick Of the Trade to accomplish a quick, positive diagnosis..
Same deal with the low fan ..we know that you can simply fool the cut-in relay for low fan for a/c by jumping the high side pressure sw. to verify the low fan circuit. And these test take nano-secounds to do and cuz we are a lazy sorts..we do not do all the complicated checking you see posters mention..we just go to the heart of the diagnosis with our bag of tricks.

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A Dalton

It's been a few days, any update?
Thanks,

__________________
1987 300TD 309, xxx 2.8.2014 10,000 mile OCI


Be careful of the toes you step on today, as they may be connected to the ass you have to kiss tomorrow. anonymous

“Be who you are and say what you feel, because those who mind don’t matter, and those who matter won’t mind.” Dr. Seuss

Hello,

Im bringing this thread back to life since i've been plagued with the same problem of the engine over heating.

The aux fans do not turn on at all. And there is only one fan speed.

I've read all the posts and so far this is what i've tried...

Pulled the blue switch with the car turned on. No change in fan speed noted.
I opened up the fuse box to check the relays. the Green fuse is in slot C. and the Blue fuse in slot B. also of note is the Blue fuse seems to be tuned 90 degrees from the orientation of the other fuses.(not sure if this means anything)


I apologize for my ignorance... I am new at this but i'm willing to learn.

Thanks!

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94 E320 - Sold

JM124, the way you've stated your problem, leads me to wonder if you may be confusing your 2 auxiliary fans with the clutch fan (the single, main engine fan between radiator and engine block). Is that possible? Your aux fans (the 2 fans at the front of the car immediately behind the grille) do have two speeds. When you pull the connector off the blue sensor (key on, cool engine), that should give you hi speed on the 2 aux fans. Does that happen?

__________________
1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't

I'm just now coming to the conclusion of my m104 cooling issues, this on a 93 300TE with the same m104 engine as your car (I also have a 94 e320 m104). Rather than recapitulating, here is the link to the forum thread:

http://mbca.cartama.net/showthread.php?t=30017

I don't go into the twin electric fans much, but certainly every other aspect of the m104 colling system is touched on. Maybe you'll find something of value in there based on my experiences.

Cheers, JAS

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94 E320
71 350SL