Freezer not cooling, checked evaporator and there is ice on top coil and bottom two coils. The rest of the evaporator is clean (no frost). I bypassed the defrost thermostat by cutting it off and jumping the wires - defrost heater did not come on so I replaced the thermostat. I then put it in diagnostic mode to test the heating element - it DID turn on and melted the ice. Does this mean my board is bad?