Carel AL50 Error Code

What does Carel AL50 mean?

AL50 on Carel µChiller and pCO chiller controllers indicates that EEV driver 2 detected that the expansion valve on circuit 2 was not fully closed when the system powered off. Like AL49, this is a valve position safety check performed at power-down. If the driver cannot complete the close sequence for the circuit 2 EEV, circuit 2 is locked out at the next startup to prevent compressor liquid slugging from an open valve.

Symptoms

• AL50 displayed on the Carel controller.
• Circuit 2 is locked out at startup following a power interruption or controlled shutdown.
• EEV driver 2 shows a valve position or power-off sequence fault.
• Manual reset required before circuit 2 can restart.

Common causes

• EEV valve 2 motor coil open or partially failed, preventing full close stroke.
• Mains power interrupted faster than the EVD driver 2 could complete its close sequence.
• EEV wiring harness on circuit 2 disconnected or intermittently open.
• EVD driver 2 energy storage insufficient to power the close sequence during power loss.

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Diagnostic steps

1. Inspect circuit 2 EEV wiring

   Trace the wiring harness from EVD driver 2 to the circuit 2 expansion valve. Check for loose connectors, damaged insulation, or broken conductors.

2. Measure EEV valve 2 motor windings

   Disconnect the EEV from EVD driver 2 and measure all winding resistances. Open or dramatically low resistance on any winding confirms motor failure requiring valve replacement.

3. Power-cycle EVD driver 2 and observe homing

   Apply power to EVD driver 2 and observe whether it performs a valve homing sequence. If the valve fails to move, the winding measurement will confirm the cause.

4. Test valve operation in manual mode

   Command the valve open and closed manually via the EVD driver 2 manual interface. Confirm the valve strokes smoothly through its full range before returning to automatic control.

5. Reset AL50 and verify normal operation

   After confirming valve 2 functions correctly, reset AL50 at the controller. Restart circuit 2 and monitor superheat and suction pressure through the first operating cycle.

When to call a professional

EEV valve replacement on circuit 2 requires refrigerant recovery from that circuit before the valve can be removed, which requires F-Gas certification. Also contact a Carel-authorized engineer if AL50 recurs on a system that was properly powered down, as this indicates either intermittent valve motor winding faults or an EVD driver hardware problem requiring component diagnosis.