The gasket on a freezer is the rubber or plastic seal around the edges of the door. When functioning properly, the gasket ensures that the freezer is airtight, which allows the appliance to function efficiently. If the gasket begins to fail, a poor seal can allow air to leak out, raising your electric bills and jeopardizing the food in the freezer. When you notice your freezer cycling on more often than usual, or not getting as cold as in the past, check the gasket and replace it if it's damaged.
Run your fingers along the outside of the freezer beside the gasket. If the frame is unusually cold to the touch, the gasket might be leaking freezing air.
Close the freezer door on a sheet of paper, with half of the sheet sticking out. Try to pull the sheet of paper free from the door. If it slides out easily, the gasket isn't sealing properly.
Place a lighted flashlight inside the freezer and close the door. Turn out the lights in the kitchen and look for light bleeding out around the gasket. If you see light escaping, the gasket is failing.
Clean the gasket with a damp cloth to remove any food particles or dust that might be interfering with the seal. Ensure that no items inside the freezer protrude far enough to press against the door and stop it from closing properly. Rearrange the freezer if necessary, and then check the gasket again. If it still doesn't seal, replace it.