Defrost system in my Whirpool french door fridge is not working. Cold area compartment gets warm a week after full defrost with the help of hair dryer while freezer keeps working normally. I checked the termostat, the heating element, they all have continuity. The only thing left to check is the control board but I have no idea how to test whether it sends voltage to heating element or not (it's supposed to do that at its own schedule). Any ideas? Could it be something other than CB?