Carel AL40

What does Carel AL40 mean?

AL40 is the No Water Flow alarm on the Carel Standard Air-conditioner (030221426). The water flow switch on a chilled-water or condenser water circuit has opened, indicating insufficient or zero flow. The controller shuts down all cooling to prevent evaporator freezing or condenser overheating without adequate water flow.

Symptoms

• All compressors and the cooling valve shut down immediately.
• AL40 displayed on the controller with alarm notification.
• Water flow switch in the chilled water or condenser water circuit is open.
• Water pump may still be running but flow is absent or below the switch threshold.

Common causes

• Water pump failed or not running.
• Air lock in the piping circuit preventing flow.
• Closed isolation valve or ball valve in the water circuit.
• Blocked strainer on the water pump suction side.
• Flow switch set too high or flow switch has failed open.

Diagnostic steps

1. 01

   Confirm water pump operation

   Verify the pump is energized, running in the correct direction, and not tripped on overload. Check the pump electrical panel for any fault indication.

2. 02

   Check and open all isolation valves

   Inspect all ball valves and isolation valves in the water circuit. A single closed valve blocks flow through the entire circuit and trips the flow switch.

3. 03

   Bleed air from the water circuit

   Open the air vent at the highest point in the water circuit. Purge air until a steady water stream flows and close the vent. Air pockets reduce effective flow below the switch threshold.

4. 04

   Clean the pump strainer

   Close isolation valves around the strainer, remove the basket, and clear any debris or scale. Reinstall the basket and open isolation valves before restarting the pump.

5. 05

   Test the flow switch

   Confirm flow is present by other means (flow meter, pump current), then check switch continuity. Replace the switch if it remains open during confirmed adequate flow.

When to call a professional

Contact a plumbing or mechanical contractor if the water circuit requires flushing, pressure testing, or chemical cleaning for biological contamination or scale. A refrigeration technician should evaluate the unit if AL40 persists with confirmed adequate flow, suggesting a faulty flow switch or controller input card fault.