Product review (5 stars): Easy to test and not too hard to replace.
This was the root cause of a wildly fluctuating freezer.  Tested bad.  Freezer would do great for 1-2 days, then it would start defrost cycle and not really ever stop defrosting.

Sadly, after a few weeks of everything working great, now the fresh foods temps are fluctuating.  I am still diagnosing the new issue.