your limit/thermostat is fine, otherwise you couldn't defrost at the board.
Is your evap fan running smoothly? A bad evap or Condenser fan motor can trash a board (jumping the board continously isn't the healthiest thing you can do for a board either)
Post some pictures of your evap frost pattern , your issue may be due to frozen condensation as opposed to a defrost failure. If your issue is frozen vents, standard defrosting may not remove all of the ice. Ice is a crystal and according to crystal growth theory, crystals grow faster when crystal is already present (seed crystal) so eliminating ALL ice is important otherwise it can overwhelm your defrost system.
btw, did you test the thermistors at the board, although diagnostics may have alerted you, testing thermistors at the board provides additional info such as wire and connection integrity.
Edited by DurhamAppliance, 20 July 2014 - 04:52 AM.