Carel AL59

What does Carel AL59 mean?

AL59 is the Driver 2 High Suction Temperature alarm on the Carel Standard Air-conditioner (030221426). The EVD electronic expansion valve driver on circuit 2 has detected that suction temperature has exceeded the high suction temperature alarm threshold for the configured delay period. Excessively high suction temperature indicates the refrigerant is significantly superheated, which overheats compressor motor windings.

Symptoms

• AL59 displayed on the controller.
• EVD driver 2 shows suction temperature above the high suction temperature threshold.
• Compressor 2 may have elevated shell or discharge temperature.
• Superheat on circuit 2 is significantly above the control setpoint.

Common causes

• Refrigerant charge low on circuit 2, allowing excessive superheat buildup.
• Electronic expansion valve on circuit 2 not opening adequately, starving the evaporator.
• Suction temperature probe S2 on driver 2 faulty, producing a false high reading.
• Suction temperature threshold and alarm delay set too low relative to actual operating conditions.
• Loss of refrigerant charge through a leak on circuit 2.

Diagnostic steps

1. 01

   Check suction temperature on EVD driver 2 display

   Read the suction temperature from the driver 2 display. Confirm whether the temperature is genuinely high or if probe S2 is faulty and generating a false high-temperature alarm.

2. 02

   Verify suction temperature probe S2 on driver 2

   Inspect probe S2 wiring and measure the output. A failing or disconnected probe can drive the suction temperature reading to the maximum, triggering the alarm without a real high-temperature condition.

3. 03

   Review suction temperature threshold on EVD driver 2

   In the EVD driver 2 manufacturer-level parameters, check the suction temperature alarm threshold. Confirm it is set above the maximum expected suction temperature under full-load, high-ambient conditions.

4. 04

   Check expansion valve operation on circuit 2

   Manually increase the valve opening via EVD driver 2 and monitor suction temperature response. If superheat drops with increased valve opening, the valve is operating but may need setpoint adjustment.

5. 05

   Check circuit 2 refrigerant charge

   Connect service gauges to circuit 2 suction and discharge ports. Low suction pressure combined with high superheat indicates refrigerant undercharge due to a leak. Leak-check all circuit 2 connections and joints.

When to call a professional

A refrigeration technician is required to leak-test circuit 2, recover refrigerant if needed, repair any found leaks, and recharge to the correct system specification. Overheated compressor windings from sustained high suction temperature can permanently damage the motor insulation, leading to compressor burnout if not promptly addressed.