Your model number is incomplete should have alot more digits and yes model number does matter...most defrost timers are inside the top of the refrigerator on the top where the light fixture is....typically it's 4-6 1/4" screws you have to take out........to test it there's usually a slot in that cabinet which allows you to take a small screwdriver and advance the defrost timer slowly and look at the defrost heater in the back of the freezer area, force it into defrost you'll usually hear a click and you'll see the bottom of the evaporator start melting ice......if you don't you have a defrost timer or bi metal/thermistor or defrost heater problem typically

I did Pull the light fixture down and was unable to find that advancements screw.