Hi Rodrigo.
The fan clutch will engage for a short time when the engine has sat for a long time, like overnight, because the silicone fluid leaks from the reservoir. Once the engine is started the clutch will engage until the fluid returns to the reservoir.
The fan clutch usually engages when the air temperature passing through the radiator and contacting the bi-metal spring on the front of the fan clutch reaches 170 degrees (F), then the bi-metal spring starts opening the valve to the silicone fluid reservoir.
Best check is to fully warm up the engine and then shut it off hot. Take the fan by one blade and try and spin it. There should be very little spin. When engaged a standard fan clutch spins at 60-70 percent of the shaft speed, so it is never fully locked, but it should be very stiff to turn.
BTW, my fun clutch still works pretty good, just ask my grandkids! LOL!