The refrigerator we picked up from Craigslist has some issues. They weren't noticeable (to me) from the start but apparently this refrigerator had been repaired at some point and those repairs should never have been done. The copper piping for the cooling system had been modified - presumably to repair some issue and according to the maintenance techs, it was a shoddy job. Ultimately, no repair tech will touch it because the previous repair was done so poorly. On top of that, it has a slow leak for the freon so over time, it needs to be recharged. At $50+ to have it recharged, it's better to recharge it myself until we end up replacing it. Here are a number of videos about recharging freon in refrigerators.
Recharging Freon in Samsung fridge
How to Add Freon To Your Refrigerator 134a
Charging R 134a Freon to Freezer [Very Quick Tutorial!]