Danfoss A02

What does Danfoss A02 mean?

On the Danfoss ERC 21X controller, A02 is a low-temperature alarm meaning the air temperature in the cabinet is too low. The measured air temperature has dropped below the controller's low-temperature limit, which can indicate over-cooling or a control fault. The display alternates between the actual air temperature and the active alarm codes, and the alarm relay is activated.

Symptoms

• Display alternates between air temperature and the code A02.
• Cabinet or case air temperature is below the set point.
• Alarm relay is activated.
• Product may risk freezing if the condition is unintended.

Common causes

• Compressor running continuously due to a stuck contactor or control fault.
• Set point or low-temperature alarm limit configured too high.
• Air sensor reading lower than the true temperature (placement or calibration).
• Cold ambient or unusually light load reducing the heat to remove.

Diagnostic steps

1. 01

   Read the alarm

   Confirm A02 on the display and note the current air temperature versus the set point.

2. 02

   Check the set point and alarm limit

   Verify the set point and the A02 low-temperature limit are correct for the application.

3. 03

   Confirm the compressor cycles off

   Check that the compressor stops at set point; a compressor that never stops points to a stuck relay or control fault.

4. 04

   Verify the sensor reading

   Confirm the air sensor is correctly placed and calibrated so the displayed temperature reflects the true cabinet temperature.

When to call a professional

If the compressor will not stop or the temperature stays too low after checking the settings, call a refrigeration technician. They can confirm whether a contactor is stuck, the controller output is faulty, or a sensor is misreading. Continuous over-cooling can freeze and spoil product, so persistent A02 alarms warrant trained diagnosis of the control and electrical components before further losses occur.