The red light and alarm on your freezer is not a door ajar alarm. This is a freezer temperature alarm. The control on the freezer thinks the temperature inside the freezer is above 39 degrees.
Since the freezer temperature is good, the electronic control in the door or the sensor that mounts on the evaporator coil inside the freezer might have failed.
This problem can also be caused by a poor connection on a wire.
Disconnect the power to the freezer for 2-3 seconds and reconnect. This will cause the control to reset itself. If the alarm remains on I recommend you go to
and get a Sears technician to repair the freezer.