648 Modern Refrigeration and Air Conditioning Copyright Goodheart-Willcox Co., Inc. loosen the screws to remove the old gasket. With the old gasket removed, start at one of the door’s top cor- ners, and slide the edge of the new gasket behind the retainer. Lightly tighten the retainer screws. Note the position of the door in relationship to the refrigerator cabinet. If the door is sagging or too high, loosen the hinges and realign the door. Pro Tip Door Liner Replacement The interior liner for the door can be replaced on older style doors that used blanket insulation. Newer foamed doors do not have replaceable liners. Mullion Heater Failure Many refrigerators with a separate freezer com- partment door have an electric heater around the door opening. This electric heater is also known as a mullion heater. It keeps ice and condensation from forming. If this heater is not working, ice buildup may keep the door from closing properly. Moisture can then enter Door Liner Replacement The interior liner for the door can be replaced on older style doors that used blanket insulation. Newer foamed doors do not have replaceable liners . and collect on the evaporator. Refer to the unit’s wir- ing diagram to determine whether or not the unit is equipped with a door heater. Defrost System Failure An automatic defrost system should prevent exces- sive frosting of the evaporator. If an automatic defrost is not working properly, ice may build up on the evapo- rator, greatly reducing the evaporator’s efficiency. Manual Defrost Chest type freezers and nonautomatic defrost upright freezers require manual defrosting. To manu- ally defrost a refrigerator or freezer, the unit must be unplugged. The contents of the refrigerator or freezer must be stored in a cooler or in a different refrigerator or freezer until the defrosting is complete. The doors are propped open so the outside air can thaw the frost. To accelerate the defrosting process, a large pot of very hot water can be set inside the cabinet. A hair dryer or a heat gun can be used to blow hot air on the frost buildup to speed its removal. Keep the heat gun a safe distance from the cabinet walls and move it back and forth to avoid warping or otherwise damaging the cabinet walls. Caution Removing Ice Never use a sharp object to remove ice from an evaporator. Doing so may puncture the evaporator. The chance of damaging an evaporator is too great to risk forcible removal of frost in an attempt to speed up the defrosting process. While evaporator repair kits are available, the durability of a repaired evaporator is much less than that of an undamaged evaporator.. When defrosting is complete, remove any water that has accumulated. Wash the inside of the cabinet with a solution of baking soda and water and thor- oughly dry it. 25.2.4 Moisture and Ice in the Cabinet Insulation The presence of moisture and ice in the cabinet insulation means there is an air leak in the outside cabinet shell. The leak allows warm, moist air to enter this space. When the warm air strikes the cold inner liner, any moisture in the warm air condenses on the cold surfaces. When this occurs in the refrigerator cabinet, the insu- lation becomes wet. The moisture causes the insulation to lose its heat-insulating qualities. When insulation becomes ineffective, it causes the following two symptoms: Removing Ice Never use a sharp object to remove ice f rom an evaporator. Doing so may puncture t h e evaporator. Th e chance o f damaging an evaporator is too great to ris k f orcible removal o f f rost in an attem pt to speed up the defrosting process. While evaporator repair kits are a vailable, the durability of a repaired evaporator is much less than that of an undamaged evaporator Gasket material with preformed corners Magnetic strip Sealed Unit Parts Co., Inc. Figure 25-7. A universal refrigerator door gasket replacement kit. This kit includes door gasket strips and magnetic material.