Freezer does not get cold enough

We got this side-by-side frigde from a friend. They said it is not freezing anymore. So we replaced the defrost T-stat, defrost timer and the defrost heater but for some reason it will not get below 35F in the freezer. What else could it be? can somebody help me out on this? :confused:

Here are your parts
http://www.appliancepartspros.com/partsearch/modelsearch.aspx?model=FRS24WSGW2

Did you replace the defrost components because there was a defrost problem or was it just a guess?

Is the compressor cycling on/off or running continuously, except when it goes through a defrost cycle?
You can usually hear the compressor running. Also you should be able to feel it vibrating and it should be warm.

Check that the condenser coils are clean and that the condenser/compressor fan is running.
Check that the evaporator fan in the freezer is running. It is required to pull air through the evaporator coils to cool it efficiently.

If the above are OK and compressor is always on, remove the cover from inside the freezer so you can see the evaporator coils.

If there is no frost or just frost in one area on the coils then you have a sealed system problem. This will be an expensive repair and it usually makes more sense to put the dollars towards a new unit.

If the compressor is cycling then the thermostat (Item 21 in Section 5) would be at the top of the list.

The above assumes that the compressor is starting OK and is not buzzing/clicking on/off while trying to start.