Whirlpool American style Fridge Freezer Evaporator freezing

Model No S25D RSS33-A/G
Good morning.
I have an issue with evaporator coil inside the freezer section freezing over. This prevents the fan from blowing cold air into the fridge, thus the result is a warm fridge.
Living in the Philippines and having bought the fridge like 15 yrs ago, service techs dont exist here.
2 questions/
1..Does anyone know the resistance of the defrost heater in its working condition? (Besides 10 – 150 Ohms)
2..Does anyone know how to test the defrost thermostat for functioning ie values on the wires?
Cant really afford to buy both parts and just “hope” it will fix my issue.

Thanks in advance of any assistance.