Carel AL008

What does Carel AL008 mean?

AL008 on the Carel Heos system controller indicates an AC (air conditioning) system alarm. The controller has received a fault signal from the connected AC system — typically a chiller or DX unit connected to the Heos MT or LT water circuit — and shuts off the AC system output command. The alarm resets automatically and activates immediately upon detection.

Symptoms

• AL008 displayed on the Heos system controller.
• AC system output command is de-energized.
• The connected air conditioning system stops operating.
• Automatic reset is attempted by the controller.

Common causes

• The connected AC unit's own internal alarm contact has opened (e.g., DX unit high pressure, low pressure, or inverter fault).
• Wiring fault on the digital input carrying the AC system alarm signal to the pCO.
• Power supply interruption to the AC system.
• AC system commissioning incomplete — alarm input not correctly configured in the pCO.

Diagnostic steps

1. 01

   Check the connected AC system for local alarms

   Access the AC system's own controller or display and identify any active alarms. The AC unit's internal fault is the most common cause of AL008 on the Heos system.

2. 02

   Inspect the AC system alarm digital input wiring

   Trace the wiring from the AC system alarm contact to the Heos pCO digital input. Verify the wiring is intact and the contact state matches what the pCO configuration expects.

3. 03

   Verify AC system power supply

   Confirm the AC unit has power and all local circuit breakers are closed. A power interruption to the AC system will open its alarm contact and trigger AL008.

4. 04

   Clear the AC unit alarm

   Resolve the AC system's internal alarm condition per the AC manufacturer's procedures. Once the AC unit alarm is cleared, the contact should close and AL008 should auto-reset.

5. 05

   Confirm AL008 clears

   Verify AL008 clears automatically after the AC system fault is resolved and the alarm contact returns to the normal (closed) position.

When to call a professional

Diagnosing the AC unit's internal fault (e.g., refrigerant circuit pressure fault, inverter fault) requires the manufacturer's service documentation for that specific AC unit and may require a refrigeration technician. If the Heos pCO digital input wiring or configuration is the issue, a Carel-authorized technician should be contacted.