Greg, the evaporator defrosts and drains to a pan on top of the compressor, or nearabouts.
The heat from the compressor is intended to dry the pan, combined with the air from the condenser fan underneath the fridge.
Sometimes there is a heater under the pan and it fries.
More likely, the condenser is slap full of fur, cat hair, and dust. It needs cleaned.
Then the air will flow properly again.
Another thing that can happen is that the cardboard pieces that they stuff in there to guide the air, they fall out and people throw them out. That's bad because the air won't flow to the pan and evaporate the water.
If the fridge is working well enough, that's your issue.
Get it all clean under there, make sure the fan is working (if there is one), and you'll also save a ton of electric.
