Commercial Refrigerators do not have a defrost cycle with heat. They use the compressor off cycle to defrost the coil. The one cycle is at 36F to 38F degrees to facilitate this defrost. And that is why the evaporator fans run 24/7.
Now the Condenser fan only runs when compressor is running. Unless the condenser is dirty, air restricted, or the fan is not up to speed. Then the compressor trips out on high load/temp. But the fan continues to run because they are wired in Parrell.
Evaporator fans are in the box. Condenser fan is part of the condenser and compressor section.