Carel AL53

What does Carel AL53 mean?

AL53 indicates that the S2 probe on EVD Driver 2 — typically the suction temperature sensor for Circuit 2 — is faulty or disconnected. In the Carel Standard Air-Conditioners program, this probe feeds superheat calculation for the Circuit 2 electronic expansion valve. Loss of this signal causes Driver 2 to shut down Compressor 2 in a controlled sequence as a protective measure.

Symptoms

• AL53 displayed on pCO terminal with Compressor 2 shut down in controlled sequence
• Driver 2 suction temperature reading absent or frozen on the controller display
• Circuit 2 cooling output lost; Circuit 1 continues normally

Common causes

• NTC suction temperature probe wired to EVD Driver 2 S2 input has failed or disconnected
• Wiring break or loose terminal in the probe cable between the suction line and the EVD driver board
• Probe connector corrosion due to moisture or refrigerant exposure
• Incorrect probe type configured in EVD Driver 2 parameters

Diagnostic steps

1. 01

   Inspect S2 probe wiring on EVD Driver 2

   Shut down the unit and trace the S2 cable from the NTC probe on the suction line to EVD Driver 2's S2 terminal. Look for loose screws, chafed insulation, or connector corrosion.

2. 02

   Measure NTC resistance

   Disconnect the S2 probe wires at the EVD driver and measure resistance. A standard CAREL NTC reads approximately 10 kΩ at 25°C. Open circuit or near-zero resistance confirms probe failure.

3. 03

   Re-seat connectors and retest

   Clean the terminals, reseat the wires at the EVD Driver 2 terminal block, and power up. If AL53 clears and a plausible temperature reading appears, the fault was a loose connection.

4. 04

   Verify Driver 2 probe type parameter

   Enter EVD Driver 2 service parameters and confirm S2 is set to NTC probe type. A configuration mismatch causes the driver to flag a valid probe as faulted.

5. 05

   Replace probe and reset alarm

   If the probe has failed, install a replacement CAREL-compatible NTC suction temperature probe. Reset AL53 and confirm Compressor 2 restarts with stable superheat control.

When to call a professional

If Compressor 2 trips on AL53 again within the first operating cycle after probe replacement, the EVD Driver 2 input circuit may be damaged. Board-level diagnosis requires a Carel-authorized technician. Recurrent probe failures at the suction line location may also indicate liquid refrigerant flooding that is physically destroying probes — a refrigerant circuit issue requiring professional diagnosis.