Carel AL29

What does Carel AL29 mean?

AL29 on Carel µChiller and pCO chiller controllers is a serious alarm generated from a configurable digital input. When the digital input assigned as a serious alarm contact opens, the controller shuts down the entire unit and displays AL29. This input is typically wired to a critical safety device — such as a refrigerant leak detector, a high-water-temperature safety thermostat, or a fire suppression signal — whose operation demands an immediate unit shutdown.

Symptoms

• AL29 displayed on the Carel controller.
• Unit shuts down completely — all compressors, pumps, and fans off.
• The safety device connected to the digital input has opened its contact.
• Manual reset required; unit will not restart until the alarm is cleared.

Common causes

• Critical safety device wired to the AL29 input has detected an actual fault condition.
• Wiring to the AL29 digital input terminal is broken or disconnected.
• Safety device (refrigerant detector, safety thermostat) has failed open-circuit.
• Configuration error assigning an incorrect device to the serious alarm input.

Diagnostic steps

1. 01

   Identify the device wired to the AL29 input

   Consult the site wiring diagram to determine which safety device drives the AL29 digital input. Do not assume it is a wiring fault before verifying the safety device.

2. 02

   Inspect the safety device for an actual fault

   Check the referenced device — refrigerant detector alarm panel, high-temperature thermostat, or remote safety switch — for a genuine alarm indication.

3. 03

   Verify wiring continuity to the digital input

   With power off, test continuity across the wiring from the safety device contact to the controller digital input terminal. Broken wiring is confirmed by open circuit.

4. 04

   Reset the safety device if genuine

   If the safety device has detected a real condition, resolve the underlying hazard (e.g., ventilate and clear a refrigerant alarm) before resetting the device.

5. 05

   Reset AL29 at the Carel controller

   After the safety device contact has re-closed and the condition is safe, perform a manual reset of AL29. Monitor the unit through the first complete operating cycle.

When to call a professional

AL29 is a serious, unit-shutdown alarm wired to critical safety devices. Never bypass or ignore this alarm. If the source device indicates a genuine hazard — particularly a refrigerant gas alarm — evacuate the area and contact emergency services before re-entry. A licensed refrigeration engineer must investigate any refrigerant leak and a qualified electrician must diagnose any wiring fault in the safety input circuit.