Your model number is incomplete , but all the ones similar to yours took part WR50X10006 .
It looks like it has L53-40F on the side. L is limit 53 degrees F is when it opens and shuts down the defrost element.
-40 is the temperature it closes at. That is 53 - 40 = 13 degrees Fahrenheit.
So it has to get to 13 degrees to complete the circuit for defrost .
GE WR50X10006 Thermostat Def - AppliancePartsPros.com