Carel AL77

What does Carel AL77 mean?

AL77 means the configuration of EVD Driver 2 is incomplete. The Carel Standard Air-Conditioners program requires the EVD expansion valve driver to have its essential parameters — refrigerant type, valve model, pressure probe type, and control mode — correctly set before it can manage Compressor Circuit 2. AL77 fires when the driver's commissioning setup is missing or contains invalid entries, causing Compressor 2 to shut down immediately.

Symptoms

• AL77 displayed on pCO terminal with Compressor 2 stopped immediately
• EVD Driver 2 display shows an incomplete commissioning state or default parameter values
• Circuit 2 non-functional; the driver will not attempt superheat control

Common causes

• EVD Driver 2 was replaced or factory-reset and has not been recommissioned
• Required configuration parameters (refrigerant, valve type, probe type, control mode) were not saved to the driver
• pLAN or tLAN communication loss during initial commissioning left the driver in an unconfigured state
• Firmware update on the EVD driver reset stored parameters to defaults

Diagnostic steps

1. 01

   Access Driver 2 commissioning mode

   Connect the CAREL display accessory (EVDIS00**0) to the EVD Driver 2. Navigate to the guided commissioning procedure, which prompts entry of the four key parameters in sequence.

2. 02

   Set refrigerant type

   Select the refrigerant used in Circuit 2 from the driver's refrigerant list. Confirm the selection matches the system nameplate and the refrigerant loaded.

3. 03

   Configure valve model and pressure probe type

   Enter the electronic expansion valve model number and select the pressure transducer type (ratiometric or 4–20 mA) connected to Driver 2 inputs S3 and S4.

4. 04

   Set the control mode

   Select the main control mode (typically superheat control for standard refrigeration/AC applications). Save all parameters and confirm the driver exits the commissioning screen without errors.

5. 05

   Reset the alarm and verify restart

   After completing commissioning, press ALARM on the pCO terminal to reset AL77. Compressor 2 should restart and Driver 2 should display live superheat values within a few minutes.

When to call a professional

If the driver repeatedly returns to an unconfigured state after commissioning, the EVD Driver 2 EEPROM is likely damaged. Board replacement and factory commissioning by a Carel-authorized technician is required. Also engage a professional if you are unsure which refrigerant, valve model, or control mode applies — incorrect entries can cause liquid slugging or compressor damage.