No, I do not know the composition of MB coolant other than it is a phosphate-free ethelene-glycol compound. I understand it is specially buffered to have a more neutral pH and it is less damaging to the plastic parts in newer MB systems. Also, Zerex G-05 is supposed to be the equivalent coolant and is often easier to find. It says on the jug it is MB approved, and I've heard that Dupont makes the MB house-brand coolant for MB in this country. As for Redline, it is supposed to be fine with all coolants, but possibly not as effective as when using it with plain water.

Mine too.

Redline's website specifically mentions ethylene glycol based coolants, good enough for me.

Okay so I retested things just now.

I see no resistor in the fan circuit.

I can get the fan to spin by bringing +12V to the red wire in the fan harness only. Which is odd, it shouldn't run without hooking up ground to the black wire. Per normal conventions the red wire should connect to Pin 87 of the relay and the black should connect to ground. Obviously the fan is getting ground from something. The other odd thing is I can't get the fan to spin backwards by connecting +12V to the black wire.

I have continuity between ground and pin 87 of the relay pictured above.

I do not have continuity between pin 87 and the yellow wire that is supposed to feed the fan 12V.

I have continuity from the other wire in the harness, a brown one, to ground.

So from this I conclude I do not have the correct relay. Which makes me wonder about the temperature sensor I was looking at. It must not be the correct one either - as it actuates the relay I have been playing with.

Can anyone confirm the location in the attached picture is the correct temperature sensor in the thermostat housing?

There is also continuity between the red wire in the fan harness and ground. This is the one that will turn on the fan with +12V.

Weird.

< I do not have continuity between pin 87 and the yellow wire that is supposed to feed the fan 12V.
I have continuity from the other wire in the harness, a brown one, to ground.
>

OK


Just take the yl fan feed [fan unplugged] and put the meter lead in that connection..now go to the relays and see which/where that yl winds up at the relays.
You saigd you had the schematic..I do not,,can I get a copy?

I did not get any answers from some quetions, so I am not sur where you stand

Does the a run with direct 12v ??
And on the jumper test I mentioned from 30 to 87 with relay unplugged.
you said you already did that in a prevoius post, but I only see where you took a V reading across 30 /87...thats not the test . The test is a jumper and after the jumper is installed , you take a reading at 30 to see if the load draw of the fan has cauded the fuse to DROP the connection..Benz fuse ends are famous for dropping power UNDER load..that is the test I was trying to get to.

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A Dalton

OH..

How many wires are in the fan harness?
That may be a 2 speed fan motor

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A Dalton

Ahh. Good to know, I visually inspected all the fuses I could find and found none that looked blown.

I'll be sure to do this when I dig up the correct relay.

Just two.

I'm going to pull the fan off and inspect it.

OK

Then this is the important part that I asked earlier..
Does the schematic show a R15 resistor in the aux fan circuit.
I did not think they used them that far back, but I have a parts book here that shows the 280se 4.5 did...that could be the problem if it has that circuitry, so look for that on schematic and look for a ceramic resistor in the harness behind the driver headlamp if it shows an R15 in schematic.

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A Dalton

>> Yeah, we know so well.

Benz fuses loose the connection at the ends in their holders , and all is required is to spin them in the holders.

So common , specially in car that have sat, that a Vet tech goes there before he even starts diagnosing an electrical feed problem

How many post I see where we say "Spin fuse #4 " and they post back. " WOW , that fixed it !!!

Just more Benz tricks....

No resistor in the schematic.

I might be able to scan it tomorrow for you.

I was able to find the correct relay. It was one of the two relays by the ECU, as someone mentioned earlier. I still had no function when I shorted the dryer switch.

The relay was very dirty, so I pulled it and cleaned the terminals and cleaned the sockets with q-tips. After that I spun all the fuses I could find in the engine bay. I was then finally able to get the fan to come on by shorting the dryer switch. Still no dice on the thermostat mounted temperature switch.

The thermostat mounted temperature switch is actually actuating the double throw relay circled with red, not yellow.

I also disassembled the fan/condenser assembly and cleaned everything.

Edit: Forgot picture.

Attached Thumbnails

 

Good

Any "Clicking" when you ground the temp sw?


To trace that wire from the temp sw to the correct relay, just unplug the sensor and hook continuity lead there , with other lead going to the relays # 85 terminal. The temp sensor simply grounds the coil of the relay to complete the circuit [ it is a switched ground] for the relay coil.
So , when you find that relay, you should have 12v at 86 and when you ground 85 , the relay should pull in [ click]
Then you have the relay load side [30/87 contacts] for the actual fan switching on/off when coil pulls them closed.

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A Dalton

As I noted previously that this sensor is activating a double throw relay, which is circled in red in post 43. I forgot to add the picture at the time.

The only double throw relay I see in the schematic is the relay for the idle speed increase solenoid and the magnetic coupling. The wire to the temperature switch has continuity with pin 85 of this relay.

The schematic shows that pin 85 should go directly to ground.

The only reason I can think of to wire this sensor into pin 85 is to turn the A/C off when the temperature reaches whatever the sensor is set to. The sensor currently does not have continuity with ground. This sensor appears new and the wire has an autozone special female plug on it.

Either the car has been modified or it differs from the diagram and does not have a secondary coolant temperature method to turn on the aux fan. The wire does come out of a bundled harness, but appears to be stretched. Could be simply from replacing the connector or could be from modification.

So I guess I need to check to see if pin 87A is connected to the magnetic coupling and idle speed increase solenoid. If it is, then I am correct.

Thanks for your help.