Carel AL17

What does Carel AL17 mean?

AL17 on Carel µChiller and pCO chiller controllers signals that the electric heaters have been commanded off by an active alarm condition. In configurations where auxiliary electric heaters are used for anti-freeze protection or heat-pump supplementary heating, AL17 activates when a safety input (such as a heater thermal cutout or a configurable digital input alarm) opens and forces the heater output off. The alarm is manual-reset.

Symptoms

• AL17 displayed on the Carel controller.
• Electric heater outputs are de-energized.
• Anti-freeze or supplementary heating is unavailable.
• Manual reset required after the alarm condition is resolved.

Common causes

• Heater thermal cutout (safety thermostat) tripped due to heater overtemperature.
• Heater thermal overload relay tripped due to excessive current draw.
• Digital input configured as heater alarm interlock has opened.
• Controller parameter configuration incorrectly enabling AL17 from an unrelated digital input.

Diagnostic steps

1. 01

   Locate the heater section and inspect for overtemperature

   Open the heater assembly access panel and check the heater elements and safety thermostat for signs of overheating — discoloration, burning smell, or visibly damaged elements.

2. 02

   Reset the heater thermal cutout

   If the heater thermal cutout has tripped, allow the heater to cool for 15 minutes, then press the manual reset button on the cutout device.

3. 03

   Check the heater thermal overload relay

   Inspect the motor control panel for the heater overload relay. If tripped, reset it and measure heater running current to confirm it is within nameplate rating.

4. 04

   Verify the alarm interlock digital input

   Identify which digital input drives the AL17 alarm on this controller. Check the wiring and the physical device connected to confirm the contact has re-closed after the fault resolved.

5. 05

   Reset AL17 at the controller

   After corrective action, perform a manual reset of AL17 at the Carel controller and verify heater outputs re-energize as expected.

When to call a professional

Contact a licensed electrician or refrigeration engineer if heater elements are visibly damaged, if the thermal cutout trips immediately after reset, or if current measurements show the heater is drawing well above rated current. Electric heater circuits operate at full mains voltage and high current; repairs require proper isolation and electrical qualifications.