Carel AL018 Error Code

What does Carel AL018 mean?

AL018 is a flow switch alarm on the LT (Low Temperature) pump circuit in the µChiller. The flow switch digital input has opened, indicating insufficient or zero water flow through the LT circuit. The controller shuts down the affected circuit to prevent evaporator freeze-up and compressor damage from operating without adequate water flow.

Symptoms

• Compressors on the LT circuit shut down immediately.
• AL018 displayed on the controller with buzzer and alarm LED active.
• Water flow switch in the LT circuit is not making contact.
• LT pump may still be running but flow is absent or below threshold.

Common causes

• Air pocket or vapor lock in the LT water circuit blocking flow.
• LT pump 1 or pump 2 has failed to start or is running in the wrong direction.
• Blocked strainer or filter upstream of the flow switch.
• Flow switch set point adjusted too high or the switch has failed.
• Closed isolation valve or service ball valve in the LT circuit.

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Diagnostic steps

1. Verify pump operation and rotation

   Confirm the active LT pump is energized and rotating correctly. Check for the correct phase sequence if recently serviced or rewired.

2. Bleed air from the circuit

   Open the air vent at the high point of the LT water circuit. Purge air until a steady stream of water flows and close the vent. Air locks cause false low-flow conditions.

3. Inspect and clean the pump strainer

   Shut down the pump and close isolation valves. Remove the pump strainer basket and clear any debris or scale buildup. A clogged strainer dramatically reduces flow.

4. Check all isolation valves

   Walk the LT circuit and confirm every isolation valve is fully open. A single partially closed valve can reduce flow below the flow switch trip point.

5. Test the flow switch

   With flow confirmed by physical observation, measure the continuity across the flow switch terminals. Replace the switch if it does not close under confirmed adequate flow.

When to call a professional

Contact a refrigeration technician if adequate water flow is confirmed but the alarm persists, indicating a faulty or incorrectly calibrated flow switch requiring replacement. Also call a professional if the LT water circuit requires pressure testing or flushing for scale or biological contamination, which involves chemical treatment beyond basic field troubleshooting.