Hi.
Most likely there is the defrost system problem.
First remove the evaporator cover (inside the freezer).
Locate the defrost thermostat and defrost heater.
Check those two parts for continuity. Remember, that the
thermostat must be ice cold.
Replace the part which has no continuity.
If both of them checks out good - replace the control board located at the rear near the compressor.
The defrost thermostat
Part number: 2321799 
The defrost heater
Part number: 2210737 
The control board
Part number: W10219463 
Here are the breakdown diagrams and
Replacement parts for Whirlpool KSCS25INSS01 REFRIGERATOR | AppliancePartsPros.com
Thank you. Post the results.
Simon.