Refrigerator is not cooling. trying to troubleshoot the problem. still some air flow

Question

trying to troubleshoot the problem. still some air flow coming
through the vents, very light, but not cold at all. what's the
most likely reason? i'm handy enough to be able to change out
parts but need help pinpointing where to start.

other symptoms: a motor kicks on and hums for a few seconds and then turns off.