Mercedes W124 Cooling Fan Hack (2) 

Real helpful input.

Thanks, I did replace the fan clutch , research showed that it doesn't fully lock up at idle, locks up at about 3K rpm, so when its 100F in stop and go traffic its just spinning doing nothing to cool engine lol, the aux high speed fan supposed to cool it down for idling in traffic, I put a switch on dash for high speed fan, boy does that cool it down fast!

Again, great stuff. Keep the videos coming!

Thanks, yeah the 2 pin sensor tests good, replaced electrical connector, 2 wires, one is blue grey, that one on the schematic is labeled auxiliary fan sensor input for push button unit (CCU) verified I have continuity on that wire, other wire is brown and yellow, it also leads to CCU , labeled sensor inputs, it has 4 or 5 sensors on it, one sensor outside, others are inside cabin, pretty sure all those sensors are for automatic CCU function, did not test those sensors because blue wire is the main trigger for CCU, at least , will test ground signal at brown yellow wire, good ideaI think lol. That’s the only wire I did not test, could be a issue? Some things that really confuse me, Pin 13 CCU, I can fire high speed fans on it, key on, apply 12 volts to it or ground wire? Bizarre! Also K9 relay, test pin sockets, key off, 3 test as grounds, one at zero, then same test with key on, 3 sockets test at 12 volts? it’s like they switch from ground to positive signal, bizarre. Did bridge the coolant sensor wires, still no fans, years ago when we got the car, worked on interior lighting issue, found multiple ground wires cut under console, repaired them, but who knows what some stereo installer did, maybe more cut grounds?

@@mygermancars7264 is your k9 relay a 6 pin or 5 pin? I think it should be a6 pin double contact relay. Take out that relay and swap it with another relay, 5 or 6 pin, then turn key on and pull the 2 pin connector off the coolant temp sensor and see if fan kicks on high. I just verified that it should still kick on with a 5 or 6 pin on my 201. Also the blue wire leading to the ccu to the sensor is designed to cut off the ac when the temp exceeds a certain degree, 110, I believe, to prevent overheating, then it turns back on once temp is brought back down. High speed in regards to the pressure sensor on receiver drier, same thing. Cuts ac off at like 20+ bar of pressure, then back on once pressure drops. I spent a great deal of time studying all the wiring of the m103 in regards to the cooling system as I live in a desert and the temps are 115+ all summer.

High speed K9 is 4 pin, K10 is 5 pin, original ones tested good on bench, but installed brand new ones.

Will test for ground signal at brown sensor wire today, will post results. I’m really really close to ditching this system and installing a reliable electric cooling fan setup, searching for proper fan shroud and fan that fits, sensor control, relay, bigger alternator etc.

Its raining perfect, tested sensor connector, unplugged, get ground signal on both wires, used battery for neg connection.

I put that tape on lol, had to remove original tape to verify wire colors, deal is wire colors are different than schematics I have, my car is a 1992, vin card show delivered to USA late 1991, closest schematics I found was for 1990, if I had exact one for my year it would be a lot easier, things like pin 11 is high speed trigger wire according to schematics, on mine it’s pin 13! See what I mean? All wires in both 14 pin connectors lay down perfectly, wire loom was untouched till I got in there. Fun uh.

@@mygermancars7264 Yep, been there. Well either way, move all the wires up one position and the problem will be fixed.

Thanks man for your help! I’ll look at schematic again and look at pin out, right side , pin one and two are empty, no wires to them, one schematic shows that’s correct.

@@mygermancars7264 yeah, but for now ignore the schematics there are far too many variations of the 124 to know if you are looking at the correct one without knowing your exact engine identification number and break point when the schematic was revised. As of '87 the automatic models through '93.... 124.023/030/050/290/226/230/090/290 were the same, not including m104, manual tranny, diesels, or the V8s

Also, worse case scenario is that if after changing the pins up a slot doesn't resolve the issue (highly unlikely) one thing you can do to get your high speed fans to run is to bypass the ballast resistor (@17:14) for low speed fans by moving the wires from the rear post of the resistor to the front. So instead of this: (fan wire)------[RESISTOR]----(fan wire), you have this: (fan wires)========[RESISTOR]xxxx(__no wires__). So when you run the ac, the fans will just kick on in high speed instead of low speed.

When I have to remove parts I clean and paint with High heat paint.

That’s what I should have done long ago, but the purests on BenzWorld said keep it stock, they just don’t understand how hot it gets here!

@mygermancars7264 I used a pair of mishimoto 12 in fans and davies craig digital fan controller. Easy install and very reliable. You can program desired operating temp. I got tired of my car running hot and power loss due to fan. You don't realize how much power loss there is from fan till it's gone. I would never go back to original fan.

Shoot me a email, artbyleclerc@gmail.com , I haven't had and cooling issues on my SL, but they are similar to W124.