A model number may help others help you.

Why did you replace the defrost parts?
Were the evaporator coils iced/frosted over?

Since compressor and fans are running the unit should cool down so it sounds like you have a sealed system problem.

Remove the cover inside the freezer so you can inspect the evaporator coils.
If there is no frost or only frost in one area (usually where the freon enters the evaporator coils), you have a sealed system problem.
Be sure that the unit has run for a couple hours because if you check it shortly after a defrost cycle there will not be any frost.
This will be an expensive repair as you need a pro.
Often it makes more sense to put those dollars towards a new unit.