Where is the defrost timer and what does it look like?

It could be anywhere, behind the toe kick plate, next to other controls. Could even be in back of the fridge. Should look something like this. You will know it when you see it because it will have a slot in the center which you can turn with a flat blade screwdriver but can only turn clockwise.

Big Dog - see your other post. It's your fan motor. Not the defrost timer switch.