A defective seal can allow a freezer door to freeze shut. Even if this happens, you can thaw the seal without completely defrosting the freezer, which would ruin the food inside.
Unplug the appliance. Gather several towels and line the floor underneath and surrounding the freezer seal area. On an upright freeze or freezer/refrigerator, this is in front of and to the sides of the freezer opening, while a chest-style freezer should be surrounded on the front, back and sides to prevent any melting water from saturating and ruining finished flooring.
Set a timer for two hours. When the time is up, check the freezer door to see if you can easily open it. During this time, much of the ice buildup on the exterior of the freezer door seal or underneath the seal should melt. If the door still refuses to open -- without using excessive force -- set the timer for another hour and recheck. Frozen food within the freezer should remain frozen for several hours without problems.
Fill a glass with hot water. Slowly pour the water over the freezer door seal to melt any remaining ice on the outside of the door or underneath the door seal. Alternatively, hold a hair dryer several inches from the door to defrost the seal and door area.
Lift or pull open the door as the ice bonding the freezer door to the unit melts. Work carefully to avoid damaging the freezer frame or tearing the seal.
Dry the rim of the freezer where the door seals to the frame to eliminate excess moisture, which will cause the door to freeze shut again.