Carel AL44 Error Code

What does Carel AL44 mean?

AL44 on Carel µChiller and pCO chiller controllers indicates that EEV driver 1 has exceeded the Maximum Operating Pressure (MOP) timeout. The Carel EVD driver's MOP protection closes the expansion valve when evaporating temperature rises excessively, protecting the compressor from overload. If the evaporating temperature stays above the MOP limit for longer than the allowed timeout period, AL44 activates and circuit 2 is shut off.

Symptoms

• AL44 displayed on the Carel controller.
• Circuit 2 is shut down after a MOP timeout event.
• Evaporating temperature on the affected circuit was running abnormally high.
• Manual reset required; automatic reset is not configured in most installations.

Common causes

• Refrigerant overcharge causing high evaporating pressure and temperature.
• Hot gas bypass valve stuck open, recirculating hot discharge gas to the suction.
• EEV driver 1 MOP setpoint configured too close to normal operating evaporating temperature.
• High load condition with inadequate refrigerant mass flow rate through the EEV.

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Diagnostic steps

1. Check refrigerant gauges for high suction pressure

   Connect gauges to circuit 2's suction side. High suction pressure relative to the ambient temperature confirms a refrigerant overcharge or hot gas bypass problem.

2. Review EVD driver 1 MOP setpoint

   Access the EVD driver 1 parameter menu and verify the MOP setpoint (expressed as evaporating temperature) is set correctly for this refrigerant and application.

3. Check for hot gas bypass operation

   Verify the hot gas bypass solenoid valve status. If stuck open, hot refrigerant gas recirculating to suction raises evaporating temperature above MOP.

4. Inspect the EEV valve for correct sizing and operation

   Confirm the EEV valve model matches the system design specification. An oversized valve can deliver excessive refrigerant mass flow, raising evaporating temperature.

5. Reset AL44 and monitor

   After addressing the root cause, reset the alarm and monitor the evaporating temperature and superheat through a full operating cycle to confirm MOP protection is no longer activating.

When to call a professional

Refrigerant circuit pressure checks, refrigerant recovery, and charge adjustment all require F-Gas certification. A Carel-authorized engineer should also review EVD driver parameter settings if MOP timeout occurs at conditions that appear normal, as incorrect MOP setpoints can cause nuisance shutdowns or mask a genuine overcharge.