On most models, when you open the refrigerator door, the evaporator fan shuts off (and a light turns on) , via a door switch. So when troubleshooting the evaporator fan, you must open the door and press the door switch. If there are two door switches, one is for the fan and one is for the light.
Mini-refrigerators usually DON'T have an evaporator fan. Air circulates by natural convection; the warm air towards the bottom of the fridge rises and is cooled by the evaporator. Once it gets cooler, the air sinks and is replaced by warmer air from below.
Open your freezer door, press the fan door switch and listen for the evaporator fan.
If you do not hear it running, there's a problem.
If you hear a "warbling" or "whistling" sound, the fan bearings are bad. Replace as described below.
Even if you do hear the evaporator fan running, but you do not feel a strong blast of freezing air from the freezer vents, then there's a problem. Usually the ducting is choked with ice, slowing or stopping airflow.
It might be jammed with debris from the freezer, or blocked with ice, or it might have just worn out and stopped. The door switch that operates it might be defective.
If there is frost covering about one-third to one-half of the evaporator, it normally indicates one of two problems.
If thick frost is clustered around the evaporator fan, the fan motor is usually running slowly, or not at all. It might just be the door switch that failed, or it may be the motor itself. If the motor is worn out, it may or may not still rotate, and it may or may not be making noise, but it is still worn out. If the fan motor is running slowly, it will show the same symptoms.
In any case, we need to open the evaporator compartment and check the fan for problems.
Remove any access panel or tower within the freezer that houses the fan.

Now we need to remove some panels to see the frost pattern on the evaporator. So let me ask you a few short questions.
Do you have a side-by-side, a top-freezer, or a bottom-freezer machine?