The service manual for this unit is not available. From your description the problem is either the fan or the defrost system.
To test if fan has iced up you simply perform a complete defrost. If the fan restarts working, then it was blocked by ice. The damper fan motor rarely fails. For this reason you usually test other parts before going for the fan. The fan motor can be tested by energizing it directly (jumping its contacts), or by reading Ohms. A faulty temperature control can cause the fan not starting.
The problem is more commonly the defrost system. This part comprises the evaporator and it is located behing the freezer firewall. The function of the defrost system is preventing coils from freezing. When defrost system is defective you get no cooling and the compressor is usually quite busy most of the time.
In defrost system locate and replace the defrost thermostat. This is the part that most commonly fails. The thermostat can be tested reading Ohms at its terminals.
Here an example of the repair done on a different fridge: When the fridge is not cooling...