I had originally had a problem with my fan clutch not coming on at all on my 85 190e and first checked the fan clutch switch to see if it was functioning properly. When the car was warm I jumped the two pin connector that attaches to the sensor and the fan jumps to life, not on the howling mode but on medium speed which is usable. But when I installed the new fan clutch sensor, the fan still did not come on. So, I jumped the two pin connector again and the fans come on again. But strangely, when I took the jumper wires fron the connector and put them on the pins on the sensor still no engagement of the fan. I must be missing something in how this system works or maybe there is a relay that could be causing this problem? If so, please let me know its location so I can check it. Also, I think the odds that the new switch is defective are pretty remote so I am discounting that for now. Thanks in advance.

Steve

The fan clutch can only be on/off, there is no way to vary the speed except by engine speed. If it does not fully engage to lock, and it is receiving 12V, the clutch is bad.

I can't tell what you are doing to test - do you mean with the connector attached to the clutch switch, shorting at the connector turns on the fan, but shorting below the connector (directly on the pins) does not? If so, then you have the connector pulled back too far off the pins, or the connector contacts need to be burnished clean.

Steve

__________________
'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7

Well, I think you clarified one thing for me which is that once the fan clutch is engaged it automatically rotates at engine speed, which at idle is not that fast. As far as the testing went, if I just jumped the two female connectors that go onto the fan switch itself, the fan clutch engages and works fine. So theoretically, when the fan switch itself reaches proper temp, it connects the circuit inside and engages the fan clutch. But if I take single lead jumper wires from the female switch connector and connect them to the poles on the switch itself, no fan still. Jump the two female connectors again and fan comes on. Leading me to only guess that the new temp switch is failing to close the circuit when the proper temp is reached. Am missing something? Thanks.

Steve

<< Leading me to only guess that the new temp switch is failing to close the circuit when the proper temp is reached. Am missing something? >>

You do realise the sw does not cut-in til the coolant temp has reached 100C [212F] ???

Yep...gave it a little more just to make sure, but was still a no go....

The normal way to test such a switch is to connect an ohmmeter between the pins while the sensor sits in a pot of water. Bring the water to a boil and see what happens. Add a little salt to the water to raise the boiling point a tad.

If the switch contacts close in this test, then either your dash gauge is inaccurate, or the coolant is not PROPERLY flowing past the sensor.

Steve

__________________
'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7