Carel AL52

What does Carel AL52 mean?

AL52 indicates that Driver 1's electronic expansion valve (EEV) is operating in a sustained high-superheat condition. The refrigerant leaving the evaporator is exiting with more superheat than the controller's alarm threshold allows, which forces Circuit 1 offline to protect the compressor from overheating and potential damage.

Symptoms

• Circuit 1 shuts down and cannot be restarted until alarm is manually reset.
• Refrigerant suction temperature at compressor inlet is abnormally elevated.
• Evaporator capacity drops as the electronic expansion valve is not delivering adequate refrigerant flow.
• Controller display shows AL52 code with no automatic recovery.

Common causes

• Electronic expansion valve (EEV) on Driver 1 is stuck partially closed or mechanically blocked.
• Low refrigerant charge in the circuit, reducing mass flow through the evaporator.
• Pressure probe S1 reading incorrectly, causing the driver to miscalculate superheat.
• High load conditions exceeding the rated capacity of the evaporator.
• Loose or damaged wiring between the EEV driver and the valve motor.

Diagnostic steps

1. 01

   Read the superheat value from Driver 1

   Access the pCO controller menu and check the live superheat reading from Driver 1. Confirm the value is genuinely elevated rather than a sensor error.

2. 02

   Inspect the pressure probe (S1) and NTC temperature probe

   Verify probe S1 connections and check for correct pressure readings. A faulty ratiometric transducer will produce false high superheat readings.

3. 03

   Check refrigerant charge on Circuit 1

   Connect service gauges and verify suction and discharge pressures. Low suction pressure relative to saturation temperature confirms undercharge.

4. 04

   Inspect the EEV and driver wiring

   Check the cable between Driver 1 and the expansion valve for continuity and correct pinout. Confirm the valve motor responds when commanded.

5. 05

   Manually reset the alarm

   Once the underlying cause is corrected, manually reset AL52 from the controller alarm menu. AL52 requires manual reset and will not clear automatically.

When to call a professional

Call a licensed refrigeration technician if you confirm the expansion valve is mechanically blocked, if the refrigerant circuit requires recovery and recharge, or if the EEV driver board itself is faulty. Working with pressurized refrigerant systems requires EPA Section 608 certification, and replacing driver boards or valves involves energized high-voltage components.