EVCO AL12

What does EVCO AL12 mean?

AL12 on the Evco SAVE AHU controller (144SAVEU0E01) is a supply air temperature probe fault alarm. The controller has detected that the supply air temperature sensor is open-circuit, short-circuit, or reading outside the valid measurement range. When AL12 is active, the controller inhibits the supply air temperature control loop — heating and cooling regulation based on supply air temperature is disabled until the probe is restored. The alarm resets automatically once a valid probe signal is detected.

Symptoms

• AL12 displayed on the SAVE AHU controller.
• Supply air temperature display shows an error value or dashes.
• Heating and cooling control based on supply air temperature is inactive.
• AHU may operate in a fallback or minimum-heat mode depending on configuration.
• Alarm self-clears once a valid supply air temperature reading is restored.

Common causes

• Supply air temperature sensor connector is loose or has disconnected at the controller terminal.
• Sensor cable is broken or pinched in the ductwork, causing an open circuit.
• Sensor element has failed due to age or moisture ingress.
• Wrong sensor type installed — controller expects NTC but a PTC sensor is connected, or vice versa.
• Sensor is sited in a location with extreme turbulence or radiant heat that pushes readings out of range.

Diagnostic steps

1. 01

   Inspect supply air sensor wiring at the controller

   Check the sensor wiring terminals at the SAVE controller. Confirm the wires are firmly seated in the terminal block and there is no sign of corrosion or arcing.

2. 02

   Measure sensor resistance at the controller terminals

   Disconnect the sensor leads at the controller and measure resistance across the sensor at known air temperature. For an NTC sensor at 25 °C, resistance should be approximately 10 kΩ; for a PTC sensor, approximately 990 Ω. An OL reading confirms an open sensor.

3. 03

   Trace the sensor cable through the ductwork

   Follow the supply air sensor cable from the sensing element to the controller. Check for kinks, pinch points, or cable damage where the duct passes through a wall or damper section.

4. 04

   Verify sensor type matches controller configuration

   Confirm the sensor type parameter in the SAVE controller matches the installed probe. Replace the sensor with the correct type if a mismatch is found.

5. 05

   Replace the sensor if resistance is out of range

   If sensor resistance does not match the expected value for the measured air temperature, replace the supply air sensor with the manufacturer-specified NTC or PTC probe. Reconnect and confirm AL12 clears.

When to call a professional

Contact a licensed HVAC technician if AL12 persists after sensor and wiring inspection, or if the AHU has operated without supply air temperature control for an extended period and the thermal performance of the building area is unknown. Incorrect supply air temperatures during periods of AL12 can affect occupant comfort and, in healthcare or food processing environments, may have compliance implications.