'86 300E Aux Fan InOp

[d2bernhard]

Hello,

I have read many threads but can't get the answer to my question.

I have '86 300E M103 W124 with 1 Fan and the mid engine green 3 pole coolant sensor fan switch just like pmizel and csnow. Fan does not come on -- even after engine was way up over 150 C laboring in steep hill city traffic-- close to the upper white mark.

Fan works when I jump it at this switch.

Additional info -- AC is inop due to grenaded compressor, so I have is disconnected (unplugged) at the compressor. I plug AC back in yesterday while engine was super hot and still did not work.

It is my coolant sensor fan switch?

Thank You

[MrCjames]

Try bridging the the two pole connector on your Green switch, the fan should engage on high. If it does engage, suspect the three pole switch.......

[d2bernhard]

Thank You.

As my post noted, I did jump it there and it works.

Have read from others on the boards with same t-shoot step and replaced coolant sensor but did not fix. I have not been able to discover from the boards what did work in these situations.

[Arthur Dalton]

Ground the br/gy wire at the 3 pole and post what happens...

[d2bernhard]

Hello,

for the third time, when the fan is jumped at the coolant temp sensor, it comes on. Fan works when jumped and key is in position 2. Fan does not come on any other time

[Arthur Dalton]

Originally posted by d2bernhard
Hello,

for the third time, when the fan is jumped at the coolant temp sensor, it comes on. Fan works when jumped and key is in position 2. Fan does not come on any other time

for the second time , jumper the wire I mention to ground...
You are jumping the switch, which could reach ground from the br/bu wire.....
So,,, as I am looking at your schematic, by GROUNDING the br/gy wire , we will then know if it is a ground fault........

[d2bernhard]

Arthur, thank you. Sorry for my frustration due to my own misunderstanding.

And, perhaps I should clarify exactly what I did -- I pulled the 2 pole connector off the 3 pole coolant temp fan switch (the 3rd pole has a dedicated connector) and jumped those two poles with a piece of wire -- then turned the key to #2 -- fan works. Do you still want me to perform your test?

Many thanks for you patience and sorry for being a dolt!

[Arthur Dalton]

OK
The reason for my wanting you to grd the wire is so I have a starting point to refence back to the schematic.
So, because you have now explained that you have jumper with the connector off , we know the circuitry is fine and the wiring is complete.
This does leave only 3 possibles
I switch is not closing at 105c [ bad sw]
2 - car is not reaching 105c [ bad dash indicator gauge]
3 - you have a coolant air lock at the sensor [ very possible if above 2 check out ..remedy is to burp/bleed the cooling system]

[d2bernhard]

Thank you again! I will test continuity of the switch both cold and hot to see what happens. Pretty sure the dash gauge is correct. The thing was screaming hot the other day when I noticed it.

[d2bernhard]

Well, don't have AC so not sure if I got it hot enough, though I tried. It was abot the 100C with no continuity. I have ordered a new switch.

[d2bernhard]

Hello All, any ideas how to replace this item??! The only way I can see is to removing the valve cover -- I can't even get a crowfoot in there.