Open the freezer door and watch the LED. If it's off, Press in the freezer door switch and check the LED again.
If the LED still off, replace the optic boards.
If the LED will blink 1 flash every second, press in the emitter flapper door to unblock the beam. If the LED still blinking, replace the optic boards.
If it stays solid, post the result and we'll go further.
- The optic boards kit
Part number: AP3137510 
Here are the breakdown diagrams and
Replacement parts for Whirlpool KSRS25IHBT00 SIDE-BY-SIDE REFRIGERATOR | AppliancePartsPros.com
Gene.