Ako E11

What does Ako E11 mean?

On AKO advanced cold room controllers (AKO-16524A/16525A/16526 series), E11 indicates that probes S1 and S2 are reading similar temperatures — meaning there is insufficient temperature difference between the cold room and evaporator probes. This prevents the SELFDRIVE self-calibration system from operating correctly and indicates either a probe positioning problem or a refrigeration issue.

Symptoms

• E11 appears on the display.
• SELFDRIVE calibration cannot complete or has been suspended.
• Controller falls back to standard (non-optimized) regulation mode.
• Alarm relay activates.
• Cold room and evaporator temperatures are unusually close together.

Common causes

• Probe S2 (evaporator probe) is incorrectly positioned and reading air temperature close to S1 (most common).
• Refrigeration system fault causing the evaporator to warm up to cold-room temperature.
• Probes S1 and S2 have been swapped during installation or replacement.
• Refrigerant shortage causing poor evaporator performance and a warm evaporator.
• Blocked airflow over the evaporator reducing the temperature differential.

Diagnostic steps

1. 01

   Verify probe S2 position on the evaporator

   Confirm S2 is properly clipped to the evaporator coil — not hanging in free air or positioned on the return air side. The evaporator probe must sense the coldest point of the coil to provide adequate differential.

2. 02

   Confirm S1 and S2 are not swapped

   Trace the probe cables to their terminals. S1 goes to the cold-room air and S2 to the evaporator coil. Swapped probes produce identical-looking readings and trigger E11.

3. 03

   Check evaporator for ice blockage

   Inspect the evaporator for heavy frost or ice that may be insulating the probe from the coil. If heavily iced, initiate a manual defrost cycle and recheck the temperature differential.

4. 04

   Monitor refrigeration system performance

   After correcting probe positions and clearing ice, observe whether the temperature difference between S1 and S2 increases to a normal range (typically more than a few degrees). Persistent similarity suggests a refrigerant issue.

5. 05

   Restart SELFDRIVE calibration after resolving the cause

   Once the temperature differential is restored, the controller can re-enter SELFDRIVE calibration mode. Consult the AKO-16524A manual for the SELFDRIVE restart procedure.

When to call a professional

Call a licensed refrigeration technician if E11 persists after correcting probe positions and clearing ice, as the flat evaporator–cold room temperature differential is a classic sign of low refrigerant charge or a failing expansion valve. Refrigerant system diagnosis and repair require certified handling of refrigerants.