why the fan does not start when the water temperature increases very much or when AC is turned on?

Proberbly be the fan temp sensor or relay is at fault.

Thakyou for you quick answer!
And can you please tel me where can I find te temp sensor.
The relay, I think is positioned in front of fan,because there is a "small box" I'm right?

we do not have these cars in the data base, but i will have a look on line and see what i can find.