Hi mark,
I have a GE Profile bottom freezer left from the previous owners, which runs into the same issue as yours sporadically.
After accessing the cooling system (which is easy enough), i found that the evaporator fan was stuck due to an ice buildup in the condensate drain tube which backed up and froze the fan.
There could be several reasons why this may be happening... I personally find that this usually happens when the wife puts a warm pot on the bottom shelf of the fridge, although checking online points to other reasons. You will also want to ensure you are vacuuming the coils at the back of the fridge.
Anyhow, you can access the fan by pulling out the bottom few shelves and prying (carefully) the plastic cover and checking the issue. Make sure you unplug the fridge first.
If you find that there has been some ice buildup, you can start defrosting it with some boiling water, and if youre careful, start chipping away some of the ice. Have a bucket and a sponge in hand too, to clear away the water. Be sure you dont puncture anything though!
Once the area has been cleared out, you also want to be sure the condensate drain tube is clear, so pour some more boiling water through and ensure it drains out. You also want to check that the water that has drained through hasnt spilled over the reservoir in the back. If so, be sure to wipe it down.
You could probably find more answers by checking online.
E.g.
http://www.fixya.com/support/t3527430-b ... r_gds18lbr