How to fix a defrost drain that keeps freezing up in an Amana bottom freezer refrigerator
"If frost or ice is forming on freezer packages, shelving, or back wall compartment order the following kit.
Order repair kit 12002686 for both Domestic Models (115 volt) and (230 volt) International Models.
See attached Instruction Sheet for details on installing Bottom Mount Frost Kit."
There is also a duckbill grommet # 8201796 that can be installed over the outlet end of the drain tube.
This is the tube at the bottom of the unit, to the drain pan. It will prevent air from equalizing through the drain tube.
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Source: Amana bottom freezer ABB1921WEW0, defrost drain freezing up