Eliwell AL2

What does Eliwell AL2 mean?

AL2 is the low temperature alarm for probe 2 (Pb2) on Eliwell RTX-600 series controllers. It activates when the temperature measured by Pb2 drops below the configured minimum threshold. The event is recorded in the ALr alarm log. Refrigeration regulation is not interrupted by AL2.

Symptoms

• Display alternates between 'AL2' and the current Pb2 temperature reading.
• Alarm entry is created in the ALr alarm folder.
• Alarm relay activates if configured.
• Buzzer sounds if fitted and enabled.
• Refrigeration regulation on Pb1 or other probes continues normally.

Common causes

• Temperature in the zone measured by Pb2 has fallen below the AL2 low-limit threshold.
• AL2 alarm threshold set too close to the setpoint, causing nuisance trips.
• Pb2 probe is positioned near the evaporator coil and reads colder than the product zone.
• Refrigeration system running continuously, causing excessive cooling of the Pb2 zone.
• Unusual low ambient conditions affecting Pb2 measurement location.

Diagnostic steps

1. 01

   Verify Pb2 temperature reading

   Access the live data display and compare Pb2 with an independent calibrated thermometer at the same location to confirm the reading is genuine.

2. 02

   Review the AL2 alarm threshold parameter

   Enter the programming menu and check the AL2 low-limit setting. Adjust to an appropriate value for the zone being monitored if it is set too conservatively.

3. 03

   Check Pb2 probe placement

   Confirm Pb2 is installed in the intended measurement location and is not positioned in a cold spot directly adjacent to the evaporator coil.

4. 04

   Investigate refrigeration system operation

   Review compressor and valve run-times. Excessive cooling of the Pb2 zone may indicate a refrigeration system fault causing over-cooling.

5. 05

   Acknowledge the alarm and monitor

   Press any key to silence the alarm. Monitor the Pb2 temperature trend over several cycles to confirm it remains within the correct range.

When to call a professional

If the Pb2 zone is genuinely at sub-safe temperatures, or the refrigeration system is continuously running and not cycling correctly, a licensed refrigeration engineer should investigate the expansion valve operation, refrigerant charge, and overall system balance.