Hi @Flor de Maria Leon
With most refrigerators (you didn't give the make and model), the evaporator fan is located in the freezer compartment behind a panel at the back of the compartment.
To access it you have to remove the back panel ''on the inside'' i.e. access through the door at the front and remove the panel to see the evaporator unit, evaporator fan, defrost heater and defrost thermistor (or thermostat).
This fan cools both compartments, freezer and refrigerator (model dependent as some models also have an evaporator unit and fan in the refrigerator compartment also)
''If it is iced over'' then there is a defrost problem e.g. faulty heater, faulty defrost thermistor, blocked drain from under the evap unit to the evap pan under the compartments near the compressor or faulty heater power supply which is from the control board.
''If it is not iced over'' then it could be a faulty fan motor or fan power supply from the control board. Also check the door switches. The door switches not only tell the control board to turn on/off the lights but also the fan. If your model has visible door switches in the door jamb, manually operate them and check if the lights go out. The fan will not operate if either door is open. Both doors need to be shut for it to work.
'''Be safety aware''' ''disconnect the power supply from the refrigerator when working on it unless testing to see what works etc''