Kenmore Elite upright Mod. # 253.28099802 15 months old. Unit shut down completely and will not restart. Never heard any alarm, but there was a small "knocking" sound when it cycled down the night before.

The light may be staying on and creating heat, or the unit thinks the door is still open.

Or the door seal is worn and is letting cold out.

Or

It needs gas.

Have you put a thermometer inside to check the temperature? It should be 0'F +/- 2'.

https://www.google.com/search?q=Kenmore+upright+freezer.+The+alarm+keeps+going+off

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Try disconnecting power for about 30 seconds, and then restore power. This will reboot the control and maybe restart.

Check the program controller unit, check if there is any loose connection to the wiring to the controller, the relay or the motor and the power plug.
When the machine shuts down then check on the power to the unit , check the door switches, the sensors , in case there is a false alarm..

The condensate drain that takes the defrost water out of the fridge is blocked.
Pour some warm soapy water down the freezer drain and this may clear it

kenmore elite, alarm kept going on and b flashed on and off. I finaly figured out on bottom of freezer there is a battery door open it and change 9v. thats it,

alarm should go off when freezer reaches minus 18c or lower.

Is the compressor running the whole time? If so may have a problem with a refridgerant leak....check the compressor in the rear of unit, feel if its hot....may be as simple as a relay.

You can try 2 things. Unplug it for about 2-3 minutes and then replug it. It should reset itself. You can silence the alarm or muffle it. Silencing it should be hard. Disconnect it from its source. You may want to find out why it is alarming constantly. Have you called Sears and asked them?

Use a freezer thermometer and tell me the actual temperature. Or at least store some ice cream and see if it stays brick hard. Unless I have some idea of the actual temp I can't tell if defective freezer or alarm

If the venting is clogged this will happen. And that is a good thing because it is a safety measure built in to prevent fires. There is a thermostat that can tell when your dryer is over-heating,(usually caused by clogged venting by lint) and this devise tells the heating element to turn off so as not to create a fire. Clean out venting, inspect thermostats and element, replace if neccesary. You may only have to clean out the venting.