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Replacement parts for GE PSS25MGMAWW | AppliancePartsPros.com
Feel the compressor is it running/warm?
Remove the cover in the freezer and take a look at the evaporator coils.
If iced over you have a defrost problem.
If only frosted in the area where the freon enters the coil you have a low freon problem.
If no frosting at all could be you are totally out of freon or the compressor is shot.
Here is a good link
Check out #20