I'm attaching your data sheet below, do Service Test - 19 Ice Maker Fill Tube Heater Status
Here's the main control board for your model:
Refrigerator Control Board WPW10675033
Here's the fill tube and heater assembly for the lower freezer ice maker:
TUBE-WATER W11238340 / AP6333243 made by Whirlpool
click.linksynergy.com
Now, for that freezer ice maker fill tube that keeps getting iced up, the heater circuit for that is on the LED light board(aka Aurora board) at connector P2-3 to P2-4.
Pull the refrigerator out from the wall and unplug the refrigerator, then remove the cover over the circuit boards on the exterior back wall of the refrigerator, then the Aurora board is very bottom board. Then when you are ready to volt test, plug the refrigerator in first.
In your tech data sheet when you do--->Service Test - 19 Ice Maker Fill Tube Heater Status--->Control the Ice Maker Fill Tube Heater by selecting SW3 (toggle between ON and OFF) (01 = ON, 02 = OFF). You should get voltage at P2-3 to P2-4 on that LED light board(aka Aurora board).
Here's the LED light board(aka Aurora board) for your model:
W10804160 Cntrl-Elec
Jake