Look for signs of a possible door gasket leak: ice inside the freezer walls, frozen food bearing ice crystals, warmer than expected temperatures in the refrigerator, ice not forming in the ice maker or ice trays and moisture inside the refrigerator. If you see any of these, check your refrigerator.
Look at the exterior of the refrigerator. Check that the refrigerator has electricity since a lack of power causes the same problems as a leaky gasket. Look at the angle of the unit. Raise the two front legs so that the refrigerator's front legs sit 1/4 inch higher than the back two. This ensures that the door will close correctly. Check the thermostat and lower the temperature inside the refrigerator and freezer. Wait for 24 hours and look to see if any of the initial problems remain. A too warm temperature setting could cause the same problems as a leaky gasket.
Test the refrigerator gasket with the power connected, if desired. Open the door and place a piece of paper or dollar in the door gap, between the metal and the rubber gasket lining the inside of the door. Close the door and tug at the paper. Resistance from the door seal indicates no gap or leak in that portion of the door.
Repeat the testing procedure all along the perimeter of both the door to the refrigerator and to the freezer. Any areas where the paper easily pulls out from the door have a leak or gap in the gasket.
Unplug the unit if you determine the refrigerator needs a repair or replacement of the gasket. If the gasket seems fine, consult a repairman about other problems that could cause the refrigerator to not operate efficiently such as a fan motor or thermostat that needs replacing.