The high-temperature alarm sounds when the temperature inside the freezer rises 15 degrees above the set temperature so that you can fix the cooling problem and prevent food spoilage. (The exact temperature rise that triggers the alarm varies by model.)
When you hear the alarm, check the freezer electrical outlet for power because the control uses a battery as back-up power to sound the alarm (on most models) when the outlet power fails. Restore power to the freezer by resetting the house circuit breaker for the electrical outlet and the freezer will resume cooling if a power failure caused the alarm.
If the alarm goes off and you hear the compressor running, a sealed system problem such as a refrigerant leak or a failed compressor pump may be causing the problem. Have a service technician examine the freezer if you suspect a sealed system failure. A service technician will need to diagnose and fix a sealed system failure because the repair involves the recovery and recharge of the refrigerant.
If the evaporator fan inside the freezer runs but the compressor doesn't run, a failed start relay on the compressor could be preventing it from starting. Most relays will rattle if they're bad. Unplug the freezer and pull off the start relay and shake it. If it rattles, try replacing the relay to get the compressor started and the freezer cooling again. This tactic won't work for all freezer models, but it may work for your freezer if you're desperate to keep food in the freezer from spoiling and can't get a service technician to repair the freezer right away.
If the freezer cools but doesn't cool down to the set temperature, a failed thermistor may be inaccurately detecting freezer temperature or the electronic control board in the freezer may be inaccurately detecting the thermistor signal. If the freezer compartment is actually at 0 degrees when the high-temperature alarm sounds, a failed thermistor or bad electronic control board likely caused the alarm by inaccurately detecting freezer temperature.
Problems in the automatic defrost system can also prevent the freezer from cooling and trigger the high-temperature alarm. If the defrost heating element that melts frost off the evaporator fins fails, frost will cake up on the evaporator fins and interfere with cooling airflow in the freezer. A failed defrost bi-metal won't allow current to reach the heater so a failed defrost bi-metal will also inhibit cooling in the freezer. A failed defrost timer won't advance into the automatic defrost mode so the defrost heating element would never turn on to melt frost off the evaporator fins.
A failed evaporator fan can also cause cooling problems because it won't circulate air through the freezer cabinet. Replace the evaporator fan if it doesn't run when activated.
Clean dirty condenser coils because dirty coils won't cool down refrigerant before it enters the evaporator, resulting in poor cooling performance. Replace the condenser fan if it isn't running when the compressor runs because the condenser fan blows air across the condenser to help cool the refrigerant before it enters the evaporator.
Sometimes, lack of maintenance can cause cooling problems and trigger the high-temperature alarm. Perform routine maintenance on the freezer such as cleaning the door or lid seal to keep warm air from entering the freezer and triggering the alarm.
