Freezer not defrosting

Evaporator coil does not defrost. After manually defrosting, the unit operates good for about two weeks before freezing up again. I am not able to locate the break down diagrams to locate parts to troubleshoot.
Please help.

Check behind the control panel, if you have an adaptive defrost pc board AP4981837 If so, go to web site %url% for manual defrost info. There are two proceedures, one should work.