Refrigerator side freezes on lowest setting

The air damper door is likely broken. Remove the cover inlet assembly and check. Located in the fresh food section on the top back. It looks like this, and this is what you most likely need to buy. Rotate picture 180 degrees, and you'll know what part it is.

How to remove it: Remove shelves, remove air duct on back (it's on clips) below the inlet cover assembly. Remove light cover and all screws holding the light fixture on top. Remove filter. Remove all screws holding the inlet cover assembly, including the one on the right, on the filter bracket. Disconnect wiring harness plug. MAKE SURE TO TAKE NOTES ON THE PARTS LOCATION OR TAKE PICTURES!!! It's not easy to put it back, so you need to know the exact interconnection of all parts.
Once you take the inlet cover assy off, look inside from the freezer side. The door is a black rectangle piece. It's supposed to be attached to the housing. If it's not attached - replace the whole cover inlet assembly.
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Check your thermostat control, it may be faulty, it has a continuity but the sensor are not.