You'll have to empty the freezer compartment and remove the back wall to expose the evap coil and drain pan... Drain inlet should be in the center of this pan so use a hair dryer to melt any ice buildup exposing the inlet... Use a turkey baster and hot water to melt ice in the drain itself... Typically ice is the culprit in most situations but I've found other debris as well causing clogs; peas, corn, dirt, and even feathers in one drain... cheers, kooler