Ako E3

What does Ako E3 mean?

E3 indicates a fault on Probe 3, an auxiliary temperature sensor used for functions such as secondary thermal alarm zones, relay outputs (RE4/RE5), or as an additional control input depending on the controller model. The fault is an open circuit, crossed/short circuit, or temperature reading outside valid sensor limits. The controller raises the alarm relay and buzzer when E3 is active.

Symptoms

• E3 appears on the display, alternating with the temperature reading.
• Alarm relay and audible alarm activate.
• Any relay or function dependent on Probe 3 (RE4/RE5 outputs, thermal alarm 3) is disabled.
• If Probe 3 provides the secondary thermal alarm (RE4), that zone is no longer monitored.
• On dual-evaporator models, only Probe 1 controls the second evaporator in fallback.

Common causes

• Open circuit in the Probe 3 cable or at the terminal connection (most common).
• Short or crossed wiring at the probe terminal.
• Moisture ingress at the probe tip causing resistance to shift out of range.
• Probe temperature exceeds sensor limits in an extreme location.
• Incorrect probe type installed relative to controller parameter settings.

Diagnostic steps

1. 01

   Identify Probe 3 location and function in this installation

   Confirm where Probe 3 is installed and which relay output (RE4/RE5) or alarm zone it controls. This determines the impact of the fault on the system while repairs are underway.

2. 02

   Inspect the probe cable run

   With the controller powered off, inspect the full Probe 3 cable for damage, chafing, or exposure to mechanical stress. Check the probe tip for corrosion or water ingress.

3. 03

   Check terminal block connections

   Re-seat the Probe 3 connector at the terminal block. Tighten any loose terminals and clean corroded contacts.

4. 04

   Measure probe resistance

   Disconnect Probe 3 and measure resistance at the tip. Compare against the AKO NTC/PTC resistance–temperature table. An open or out-of-range reading confirms probe failure.

5. 05

   Replace the probe

   Install an AKO-approved replacement Probe 3. Route the new cable away from power wiring. Restore power and verify E3 clears and any dependent relay outputs resume normal operation.

When to call a professional

Call a licensed refrigeration technician if Probe 3 monitors a safety-critical zone (such as a motor winding temperature or a second cold room) and that zone has been unprotected during the fault. If E3 occurs alongside other active alarms or if the evaporator associated with Probe 3 shows icing, a technician is needed to assess system condition before returning to service.