EVCO AL14

What does EVCO AL14 mean?

AL14 on the Evco SAVE AHU controller (144SAVEU0E01) is a CO2 probe fault alarm. The controller monitors the CO2 sensor used for demand-controlled ventilation (DCV) and triggers AL14 when the sensor signal is absent, out of range, or indicates a communication fault. With AL14 active, the controller inhibits the CO2-based ventilation control loop and the relevant damper or fan speed control falls back to a fixed or minimum setting. The alarm resets automatically when a valid CO2 reading returns.

Symptoms

• AL14 displayed on the SAVE AHU controller.
• CO2 sensor reading shows an error or the display is blank for that channel.
• Demand-controlled ventilation based on CO2 level is disabled.
• Outside air damper may open to a fixed minimum position rather than modulating to CO2 demand.
• Alarm self-clears when the CO2 sensor returns a valid signal.

Common causes

• CO2 sensor power supply has failed or wiring to the sensor is broken.
• CO2 sensor has reached end of life — electrochemical or NDIR sensors typically need replacement every 5–10 years.
• Signal wiring from the CO2 sensor (4–20 mA or 0–10 V) has a loose connection at the controller.
• CO2 sensor is installed in a location with direct sunlight or moisture exposure, causing drift or failure.
• Sensor calibration has drifted beyond the controller's valid input range.

Diagnostic steps

1. 01

   Check CO2 sensor power supply

   Verify that the CO2 sensor is receiving the correct supply voltage — typically 24 V DC or AC. Use a multimeter at the sensor power terminals. No voltage indicates a wiring fault or failed power supply.

2. 02

   Inspect signal wiring from sensor to controller

   Trace the 4–20 mA or 0–10 V signal wiring from the CO2 sensor back to the SAVE controller analog input terminal. Check for loose terminal connections and measure the signal level with the sensor powered.

3. 03

   Verify the CO2 sensor is within calibration

   If the sensor is powered and wired correctly, compare its output to a calibrated reference or a known CO2 concentration (fresh outdoor air is approximately 400 ppm). A sensor reading that is significantly wrong indicates calibration drift or sensor end-of-life.

4. 04

   Check sensor installation location

   Confirm the CO2 sensor is located per the design specification — typically in the return air duct or occupied zone. Sensors in direct sunlight, near exhaust outlets, or in high-humidity areas degrade faster and produce invalid readings.

5. 05

   Replace the CO2 sensor if fault persists

   If power, wiring, and location are confirmed correct but AL14 persists, replace the CO2 sensor. Recalibrate or verify calibration of the replacement unit per the manufacturer's procedure before reinstating demand-controlled ventilation.

When to call a professional

A licensed HVAC controls technician should handle CO2 sensor replacement and recalibration on commercial AHUs, particularly where demand-controlled ventilation is required for ASHRAE 62.1 compliance or building code. Incorrect CO2 sensing in occupied spaces — whether too high (under-ventilation) or too low (energy waste) — has indoor air quality and regulatory implications that require qualified commissioning to confirm correct operation after sensor replacement.