I'm assuming the 8 in your model # is actually a B, if not please verify.

Do you mean the pan in the bottom of the outside back, the evap defrost drain pan? It dries by evaporation, so it needs the airflow generated by the condenser fan to help that. If airflow is blocked by a very clogged condenser, or being too close to the walls that can slow evaporation. Or a due to a dead of jammed condenser fan the defrost water may not evaporate fast enough.

If you mean that you have an ice sheet in the bottom of the freezer, the drain tube is probably blocked by foreign material or possibly just frozen over.