Carel AL01

What does Carel AL01 mean?

AL01 on Carel µChiller and pCO-based chiller controllers indicates that the thermal overload protection device on compressor 1 has tripped. This protection activates when the compressor motor draws excessive current — typically due to overheating — and the overload device opens its contact, signaling the controller to shut down compressor 1. The alarm requires manual reset after the compressor has cooled and the fault cause is identified.

Symptoms

• AL01 displayed on the Carel controller interface.
• Compressor 1 is shut down; cooling capacity is reduced or lost.
• Compressor motor surface is abnormally hot to the touch.
• Manual reset is required; alarm does not clear automatically.

Common causes

• Dirty or blocked condenser coils causing high discharge pressure and compressor overheating.
• High ambient temperature exceeding the compressor's design operating range.
• Low refrigerant charge causing the compressor to run in an over-heated, vapor-starved condition.
• Compressor motor winding insulation degraded, drawing excessive current.
• Thermal overload device set too sensitively or having aged out of calibration.

Diagnostic steps

1. 01

   Allow the compressor to cool before reset

   Do not attempt to reset AL01 immediately. Wait at least 15–20 minutes for the compressor motor and thermal overload device to cool before attempting a reset.

2. 02

   Inspect and clean the condenser

   Check condenser coils for dust, debris, or airflow obstruction. Clean fouled coils with compressed air or coil cleaner to restore heat rejection capacity.

3. 03

   Measure discharge pressure

   Connect refrigerant gauges and check high-side pressure. Elevated discharge pressure confirms a condenser heat rejection problem driving compressor overheating.

4. 04

   Check compressor motor current

   After reset, use a clamp ammeter on the compressor supply conductors. Current above nameplate FLA indicates a winding or mechanical fault requiring replacement.

5. 05

   Reset the alarm manually

   After corrective action and a cool-down period, reset AL01 at the controller. Monitor for recurrence within the next operating cycle.

When to call a professional

Contact a licensed refrigeration engineer if AL01 trips again shortly after reset, if compressor current is above nameplate rating, or if high discharge pressure persists after condenser cleaning. Refrigerant handling, compressor replacement, and electrical diagnosis on three-phase compressor circuits all require certified personnel.