EVCO AL07

What does EVCO AL07 mean?

AL07 on the Evco SAVE AHU controller (144SAVEU0E01) is an automatic-reset thermal overload alarm for the electric heating elements — the automatic-reset counterpart to the manual-reset AL05. The controller detects that the heater thermal protection has tripped and responds by switching the heaters off. Unlike AL05, AL07 resets without operator intervention once the heater thermal protector cools and the overtemperature condition clears.

Symptoms

• AL07 displayed on the SAVE AHU controller.
• Electric heating elements are switched off.
• Supply air temperature drops below the heating setpoint.
• Heaters automatically re-energize once the thermal protector resets (motor cools).
• If the root cause is not resolved, AL07 will recur repeatedly in a trip-reset cycle.

Common causes

• Airflow across the heater bank is temporarily reduced — a heavily loaded filter or brief fan slowdown allows heat buildup.
• Heater bank is oversized for the current airflow, causing elements to reach trip temperature during low-load conditions.
• One heater element has failed open, concentrating the full electrical load across fewer elements.
• Short-duration voltage spike caused excess current draw and tripped the thermal cutout.
• Heater thermal cutout rating is marginally too low for the application.

Diagnostic steps

1. 01

   Observe whether AL07 is recurring frequently

   Monitor the alarm history. An AL07 that resets quickly and rarely indicates a transient event. AL07 that repeats multiple times per day signals a persistent problem requiring investigation.

2. 02

   Inspect AHU filters and supply fan airflow

   Check filters for loading and replace if necessary. Confirm the supply fan is running at full speed and delivering the design airflow rate across the heater bank. Reduced airflow is the leading cause of AL07.

3. 03

   Check individual heater element resistances

   With the heater circuit de-energized, measure resistance across each element. An open element (OL reading) means other elements are carrying excess load — identify and replace the failed element.

4. 04

   Inspect heater control contactor

   Check whether the heater contactor is releasing correctly when the controller commands heat off. A contactor with welded contacts keeps heaters energized when they should be off, rapidly tripping the thermal overload.

5. 05

   Confirm automatic reset and monitor for recurrence

   Once the thermal cutout resets, AL07 should clear and the heaters should restart automatically. Monitor supply air temperature for the next 30 minutes to verify stable operation without repeated trips.

When to call a professional

Contact a licensed electrician or HVAC technician if AL07 recurs more than twice daily, if a burned or open heater element is found, or if the heater contactor is suspected of welding. Repeated thermal trips can cause progressive insulation damage to remaining elements — a technician should megger-test the heater bank insulation after repeated overload events to assess its condition.