Freezer Frosting Over Constantly

Your frost-free freezer is anything but, and you are defrosting it by hand more often than you should ever have to. This builds a fault tree that walks through the usual suspects in order: a door seal that is not sealing, a door left open too long, a dead defrost heater, a failed thermostat or thermal fuse. For anyone deciding whether to fix it or call someone.

My freezer keeps frosting over even though it's supposed to be frost-free. The ice builds up on {ICE_LOCATION} and I have to manually defrost it every {DEFROST_FREQUENCY}. The freezer is part of a {FRIDGE_FREEZER_TYPE} and the fridge section {FRIDGE_SECTION_STATUS}. Give me a fault tree that covers: door seal not sealing properly, door being left open too long, defrost heater failure, defrost thermostat or thermal fuse failure, and defrost timer or control board fault. Tell me how to test the door seal with a piece of paper, how to run a manual defrost cycle if applicable, and which parts I can test with a multimeter before ordering anything.