EVCO AL11

What does EVCO AL11 mean?

AL11 on the Evco C-PRO RACK controller signals a high discharge pressure alarm linked to the pressure regulator circuit on circuit 1. When this alarm activates, the controller commands all compressors on circuit 1 to shut down to protect them from operating against excessive head pressure. This is a higher-severity alarm than AL31 (fans-on response) — compressor shutdown is the protective action. The controller must be reset manually after the underlying condition is resolved.

Symptoms

• AL11 displayed on the C-PRO RACK controller.
• All compressors on circuit 1 are shut down.
• High-pressure safety switches on the circuit may also have tripped.
• Discharge pressure is significantly above normal operating range.
• Alarm requires manual reset after the high-pressure condition is cleared.

Common causes

• Severely fouled or blocked condenser coil preventing adequate heat rejection.
• Multiple condenser fans failed simultaneously, leaving no forced airflow across the coil.
• Large refrigerant overcharge — excess liquid refrigerant flooding the condenser and raising head pressure.
• Non-condensable gases (air or nitrogen) introduced during service contaminating the high side.
• High ambient temperature spike combined with reduced condenser performance.

Diagnostic steps

1. 01

   Do not attempt to restart compressors immediately

   AL11 is a protective shutdown. Allow the system to equalize pressure for at least 5 minutes before any restart attempt. Rapid restart against high head pressure damages compressor valves and windings.

2. 02

   Inspect condenser fans and coil

   Confirm all condenser fans are running. Inspect the condenser coil for severe blockage — clean aggressively with coil cleaner and rinse if needed. Check for ice on the coil in low-ambient conditions that could block airflow.

3. 03

   Check the high-pressure safety switches

   Locate the manual-reset high-pressure switches on circuit 1. If tripped, press the reset button only after the cause of high pressure has been addressed. Resetting without fixing the root cause results in repeat compressor shutdown.

4. 04

   Connect manifold gauges to measure high-side pressure

   Attach a manifold gauge set to circuit 1 high-side service ports and read actual discharge pressure. Compare to the saturation pressure at measured ambient temperature to determine whether overcharge or non-condensables are contributing.

5. 05

   Perform manual reset on the controller and monitor

   After corrective action, access the controller alarm menu and perform a manual reset of AL11. Restart the system and observe discharge pressure during the first 15 minutes of operation to confirm the condition does not return.

When to call a professional

AL11 results in compressor shutdown and almost always requires a licensed refrigeration technician to diagnose and resolve. Recovering refrigerant to correct an overcharge, purging non-condensables, diagnosing pressure transducer faults, and evaluating compressor condition after an overpressure event are all tasks requiring EPA Section 608 certification and specialized equipment.