Product review (4 stars): Solved my issue
I wasn't very happy to need this part in the first place. For an LG refrigerator that was about $2500, I would have expected it to last more than 3 years. However, I'd rather put in a $100 part than buy a whole new one.

What is this board for? It is the smaller of the 2 boards inside, and acts as the power supply to the compressor.
Symptoms: Refrigerator may be blowing air, but isn't cooling.
Touch the compressor (the large black "ball" inside the rear at the bottom, behind the large metal panel). If it is room temp or just slightly warmer (not hot), and the small condenser fan on the right is moving (which indicates the other board and thermostat are fine), then this smaller board (behind a small metal panel a bit higher up on the back should get you up and running again.
You can get these cheaper elsewhere such as encompass or other appliance parts sites, but amazon typically has quick prime shipping, so it was worth the extra cost to get the fridge back in working order quickly.