Carel AL08

What does Carel AL08 mean?

AL08 is a Heater 2 Thermal Overload alarm on the Carel Standard Air-conditioner (030221426). The thermal overload protection on the second electric reheat element has tripped, cutting off power to Heater 2. The controller logs AL08 and prevents heater operation until the overload is reset and the cause is resolved.

Symptoms

• Heater 2 de-energized immediately on alarm activation.
• AL08 displayed on the controller with buzzer active.
• Thermal overload relay on the Heater 2 circuit is tripped.
• Room temperature may drop if the unit was relying on Heater 2 for temperature maintenance.

Common causes

• Heater 2 thermal overload relay tripped due to sustained overcurrent from a partial element failure.
• Insufficient airflow over the heater coil causing overheating and relay trip.
• Overload relay set current too low for the actual heater element draw.
• Phase loss or voltage imbalance on the heater power supply.
• Heater element developing a partial short increasing current draw.

Diagnostic steps

1. 01

   Allow cooldown and reset the overload relay

   Wait 15 minutes for the heater elements and overload relay to cool. Locate the thermal overload relay in the electrical panel and press the manual reset button.

2. 02

   Verify supply airflow across heater 2

   Confirm adequate airflow is moving through the heater section. Low airflow causes heater elements to overheat even at normal current. Check fans and filters before re-energizing.

3. 03

   Measure heater element current

   With the heater energized, clamp-meter all three phases at the heater terminal block. Compare to the rated heater element current on the nameplate. Elevated current on one phase indicates a faulty element.

4. 04

   Check overload relay set current

   Verify the overload relay is set to the nameplate full-load amperage for Heater 2. An incorrectly low setting causes nuisance trips under normal operation.

5. 05

   Inspect heater element condition

   With power off, use an ohmmeter to check heater element resistance across each phase. An element reading significantly lower resistance than expected has a partial short and must be replaced.

When to call a professional

A licensed electrician should handle heater element replacement, overload relay replacement, and electrical panel work. Repeated AL08 trips after overload reset indicate a failing heater element or electrical supply problem that requires professional diagnosis to prevent fire risk or equipment damage.