Carel AL31 Error Code

What does Carel AL31 mean?

AL31 on Carel µChiller and pCO chiller controllers is a minor alarm generated from a configurable digital input. Unlike AL29, this alarm does not shut down the unit — it activates a display-only warning or a low-priority alarm output. The digital input is typically wired to a non-critical monitoring device such as a filter differential pressure switch, a maintenance reminder switch, or an auxiliary sensor.

Symptoms

• AL31 displayed on the Carel controller.
• Unit continues to operate normally; no compressor or output shutdown.
• The device connected to the AL31 digital input has opened its contact.
• Alarm is a reminder or advisory — not a safety shutdown.

Common causes

• Non-critical monitoring device (filter switch, auxiliary sensor) has signaled a fault or maintenance condition.
• Wiring to the AL31 digital input is broken or disconnected.
• Device connected to the input has failed open-circuit.
• Configuration error or an incorrect device assigned to this minor alarm input.

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Diagnostic steps

1. Identify the device wired to AL31

   Consult the site wiring diagram to determine what device drives the AL31 input — it is often a filter differential pressure switch or a maintenance contact.

2. Check the physical device for a real condition

   Inspect the referenced device. If it is a filter switch, check the filter for clogging. If it is a maintenance switch, verify whether a maintenance interval has elapsed.

3. Inspect AL31 terminal wiring

   Check the digital input wiring at both the controller terminal and the device end. Look for loose screws, broken conductors, or corroded contacts.

4. Address the underlying condition

   If the alarm is from a dirty filter, replace or clean the filter. If it is a maintenance reminder, perform the required maintenance and reset the counter.

5. Reset AL31 at the controller

   Once the digital input contact has re-closed after the condition is resolved, reset AL31 manually at the controller.

When to call a professional

Although AL31 is a minor alarm, the device connected to the input should always be investigated to rule out a developing fault. If the source device is a refrigerant detector or a safety device that has been incorrectly wired to the minor alarm input rather than AL29, contact a refrigeration engineer immediately to review the wiring and alarm configuration.