Freezer compartment has frost buildup

This can be caused by the drain hole below freezer coil being blocked by ice. You MUST remove all ice in drain under freezer coil. Use turkey baster to squirt hot water into hole and use hairdryer to defrost. Possible defrost thermostat is defective. Unit never goes into defrost, ice forms on coil and in floor of freezer. After defrosting may work OK for a week or two but gradually gets warmer because ice is blocking ports where cool air gets to refrig. May also have water in refrig box. Can also be caused by defective defrost timer.