Refrig. Damper not opening until manual defrost

GE GSS25WGMCWW side by side Refrigerator/Freezer
The refrig. side was warm.
The damper was not opening in the refrig side.
I manually defrosted the refrig./freezer for about 14 hours.
Now, the damper is opening in the refrig. side and the refrig. side is getting cool.

Question:
What would cause the refrig. side damper to not open and as a result the refrig. side gets warm, but when I manually defrosted the refrig./freezer, it now opens and the refrig. side is now getting cool?
WHAT PART needs REPLACING?

Thank you,
Soul Duck