Freezer frosts up

I have changed the thermostat,tested the heating elements for resistance,tested the timer for voltage out on defrost cycle. all are good but it still won’t defrost. what am I missing? please help
:confused:

Would it defrost if you turn the defrost timer manually? If the answer is Yes, then the defrost timer is the culprit.

  • The defrost timer [part]AP2061695[/part]

Gene.