Mercedes W201 190E 16V EVO

1.When has it it start?
I think it has to start when engine temperature reaches ~100C.
2. How does it works?
Is is thermoplate on fan or is it electrified?

1. fan engages, when cooling temperature is at 100°C
2. it's an magnetic clutch, voltage is switched via the temperature controlled switch at front of the cylinder head

If the clutch doesn't work, try to bridge the switch first, it's a red one at the front of the engine, should have three pins for your model year.
Ignition on, engine off, bridge the plug with two pins, you should hear a click and the fan should lock.
If it doesn't, check the plug for 12V at one of the pins and ground at the other pin.

The clutch of Rosi's fan had a broken wire, just at the magnet.

BTW, you do have a name to address you? I'd love to know it...

good luck,
bis denn,
Christian

1989 300TE
1984 2.3-16

From left to right:
- temp sensor for the engine temp indicator inside
- temp sensor (4 pin) for KE and EZL
- temp switch for the magnetic clutch of the radiator fan

so: the red one at the right.
should have two pins, three wich a/c

regards,
Christian