Dixell/Copeland AL01

What does Dixell/Copeland AL01 mean?

On the Dixell IC100CX iChill controller, AL01 is the low-pressure alarm delay parameter. It sets the time in seconds that must elapse after the low-pressure digital input activates before the controller signals a low-pressure alarm. This delay prevents nuisance trips during compressor startup transients when suction pressure momentarily dips below the switch cutout setpoint.

Symptoms

• Low-pressure switch digital input activates.
• After AL01 delay expires, the low-pressure alarm is triggered.
• Compressor may stop depending on system configuration.
• Alarm indicator illuminates on the controller display.

Common causes

• AL01 set too low (near zero) causing the system to trip on startup transient pressure dips.
• Refrigerant undercharge causing sustained low suction pressure that outlasts the AL01 delay.
• Faulty low-pressure switch with too-high cutout setpoint relative to normal operating suction pressure.
• Expansion valve restriction reducing refrigerant flow and pulling suction pressure below the switch threshold.
• Dirty evaporator reducing heat transfer and causing suction pressure to drop.

Diagnostic steps

1. 01

   Review the current AL01 setting

   Access the AL sub-menu on the IC100CX. Verify AL01 (delay time in seconds) is appropriate for the system startup characteristics. Typical values range from 30 to 120 seconds.

2. 02

   Monitor suction pressure during startup

   Connect manifold gauges and observe suction pressure during compressor start. If pressure recovers within the AL01 time, no further action is needed on the parameter. If it stays low, investigate the refrigerant system.

3. 03

   Check refrigerant charge

   Low suction pressure that persists beyond AL01 typically indicates undercharge or a blockage. Measure subcooling and superheat to assess refrigerant level.

4. 04

   Test the low-pressure switch

   Verify the LP switch cutout setpoint is correct for the refrigerant and application. A switch set too close to normal operating pressure generates repeated false trips.

5. 05

   Inspect evaporator coil and filter

   A fouled evaporator coil or blocked water-side filter reduces heat absorption, lowering suction pressure. Clean or replace as required.

When to call a professional

If suction pressure remains below the low-pressure switch setpoint even after AL01 delay and the system requires refrigerant addition or a leak repair, a licensed refrigeration technician must perform those services. Repeated tripping despite correct AL01 tuning indicates a system refrigerant circuit fault.