Carel AL48

What does Carel AL48 mean?

AL48 on Carel µChiller and pCO chiller controllers indicates that EEV driver 1 has detected a low superheat condition. The Carel EVD driver monitors refrigerant superheat at the compressor suction and activates low superheat protection when measured superheat drops below the configured minimum threshold. AL48 causes circuit 1 to be shut down to prevent liquid refrigerant from entering the compressor.

Symptoms

• AL48 displayed on the Carel controller.
• Circuit 1 is shut down by the EEV driver low superheat protection.
• Suction line and compressor suction pipe may be frosting or sweating heavily.
• Superheat measured by the EVD driver was below the minimum setpoint.

Common causes

• Refrigerant overcharge causing excessive liquid in the evaporator and low superheat.
• EEV valve oversized for the system load, delivering more refrigerant than the evaporator can fully evaporate.
• Sudden load drop (e.g., hot gas bypass opening) causing evaporator to flood.
• Superheat sensor probe (suction pressure or temperature) incorrectly positioned or calibrated.

Diagnostic steps

1. 01

   Check suction line for signs of flooding

   Inspect the compressor suction line for frost or heavy sweating extending back from the evaporator — evidence of liquid carry-over into the suction.

2. 02

   Verify refrigerant charge

   Connect gauges and check suction pressure against the expected saturation temperature. High suction pressure relative to load conditions suggests overcharge.

3. 03

   Review EVD driver 1 superheat setpoint

   Access the EVD driver 1 parameters and confirm the superheat setpoint is appropriate for the application — typically 5–8 K for most refrigerants in a chiller application.

4. 04

   Check the superheat sensors

   Verify the suction temperature probe is correctly clamped to the suction line and insulated. An uninsulated probe reads ambient air temperature, producing falsely high superheat and causing the valve to over-open.

5. 05

   Reset AL48 after correction

   After correcting the overcharge, valve sizing, or sensor issue, reset the alarm and monitor superheat through a complete operating cycle to confirm stability.

When to call a professional

Refrigerant charge adjustment requires F-Gas certification and must be performed by a licensed refrigeration engineer. An engineer should also evaluate whether the EEV valve model is correctly sized for the system — undersizing and oversizing both cause superheat instability that cannot be resolved by setpoint adjustment alone.