Carel AL24

What does Carel AL24 mean?

AL24 indicates the condenser temperature probe for Condenser Circuit 1 is faulty or has lost electrical continuity. The Carel Standard Air-Conditioners program uses this probe for condensing pressure control and condenser fan speed modulation. When AL24 fires, condenser fan control for Circuit 1 reverts to a default state and the alarm is logged; the unit may continue running depending on configuration.

Symptoms

• AL24 displayed on the pCO controller; condenser temperature reading absent or out of range
• Condenser fan on Circuit 1 running at fixed speed instead of modulating
• Possible high-side pressure instability if fan control relies on condenser temperature

Common causes

• NTC or PT1000 condenser temperature probe has failed — open circuit or resistance out of range
• Wiring break or loose terminal on the probe cable between the condenser coil and the pCO input
• Connector corrosion from outdoor exposure or moisture ingress at the probe terminal
• Probe mounting bracket corroded or probe displaced from the condenser coil contact point

Diagnostic steps

1. 01

   Identify the condenser probe input on the pCO board

   Refer to the wiring diagram for the specific air-conditioning unit to locate the analogue input assigned to the condenser temperature probe for Circuit 1.

2. 02

   Measure probe resistance

   Disconnect the probe from the pCO board and measure resistance with a multimeter. For a CAREL NTC, expect approximately 10 kΩ at 25°C. An open or short circuit confirms probe failure.

3. 03

   Inspect and re-seat probe wiring

   Trace the cable from the probe connector at the board back to the condenser coil. Re-seat any loose terminals and look for chafed or broken conductors, particularly where the cable passes through the panel.

4. 04

   Replace the probe if defective

   Fit a replacement CAREL-compatible condenser temperature probe to the same mounting location. Ensure good thermal contact with the condenser coil surface.

5. 05

   Clear the alarm and verify fan control

   Reset AL24 from the alarm screen and confirm the condenser temperature reading is live and plausible. Verify that condenser fan speed modulation resumes normal operation.

When to call a professional

Condenser temperature probe replacement is straightforward for a qualified technician. Call a pro if the probe replacement does not clear the alarm — the pCO analogue input board may be damaged. Also engage a specialist if the condenser fan control failure caused a high-pressure condition requiring refrigerant circuit diagnosis or charge verification.