Lennox Commercial

1. Issue Summary & Quick Assessment

The Lennox Energence rooftop fault code 135 indicates a failure in the airflow sensor or, more specifically, a failure to detect airflow within the unit. This code generally suggests that the rooftop unit’s control board has determined that there is insufficient airflow, which can lead to equipment damage if not addressed promptly.

When this error triggers, a technician or operator may observe several physical symptoms. These include:

  • The unit unable to achieve the setpoint temperature, leading to inadequate heating or cooling.
  • A visible lack of air movement from the supply vents, indicating degradation of airflow.
  • Presence of unusual operational sounds, such as high-pitched alarms or beeping from the control panel, often accompanied by warning lights.
  • Temperature differentials that do not align with expected values, further indicating airflow issues.

Before beginning any diagnostic work on the Lennox Energence unit, specific safety precautions must be observed. Ensure to:

  • Isolate the unit by disconnecting the high-voltage power supply and use lockout/tagout procedures to ensure the unit remains inoperable while diagnostics occur.
  • Be mindful of refrigerant safety. If refrigerants are potentially involved, ensure compliance with local regulations concerning handling and venting.
  • Wear appropriate personal protective equipment (PPE) throughout the diagnosis process to maintain safety.

2. Technical Parameters & Root Causes

There are several potential root causes for the fault code 135 in the Lennox Energence rooftop unit:

  • Faulty Airflow Sensor: The airflow sensor may be malfunctioning and sending incorrect signals to the control board, causing it to register insufficient airflow.
  • Voltage Fluctuation: Voltage inconsistencies can lead to erratic sensor performance. A low voltage reading (below 20V for control signals) may contribute to the problem.
  • Airflow Restrictions: Physical obstructions in the ductwork or filters can lead to insufficient airflow. A pressure drop of over 0.5 inches of water column at the sensor indicates possible blockage.
  • Wiring Issues: Corroded, loose, or damaged wiring connections can interfere with signals sent from the airflow sensor to the control board. Use a multimeter to check for continuity; resistance should ideally be under 5 Ohms.

For each of these causes, technicians should monitor the following technical parameters when troubleshooting:

  • Airflow sensor voltage output should be between 2 to 5 volts DC during normal operation.
  • As mentioned, any pressure drop greater than 0.5 inches of water column at the sensor can indicate an airflow issue.
  • Resistance readings from the sensor should grace around 1 to 2 kOhms depending on the unit configuration and the type of sensor installed.
  • Check input voltage to the control board; it should remain steady at 24 volts AC.

3. Step-by-Step Diagnostic & Troubleshooting Procedure

To systematically diagnose and attempt to repair the airflow issue indicated by fault code 135, follow these steps:

  1. Power Off the Unit: Ensure the unit is completely powered down by removing the power disconnect. Implement lockout/tagout procedures to maintain safety.
  2. Inspect Air Filters: Check and replace any clogged or dirty air filters as this can obstruct airflow. Filters typically require replacing every 3-6 months.
  3. Examine Ductwork: Conduct a visual inspection of the ductwork for any physical obstructions such as debris, collapsed sections, or damage that could impede airflow.
  4. Test the Airflow Sensor: With a multimeter, check the voltage output of the airflow sensor. If the output is outside the expected range (2-5 volts), consider replacing the sensor.
  5. Inspect Wiring: Trace the wiring from the airflow sensor to the control board. Inspect for signs of damage or corrosion. Use a multimeter to check for continuity. Ensure resistance is minimal (under 5 Ohms).

4. Prevention & Maintenance Best Practices

To minimize the chances of experiencing fault code 135 in the future, the following preventative measures should be implemented:

  • Establish a Seasonal Maintenance Schedule: Schedule routine inspections bi-annually to check filters, sensors, and other components.
  • Regularly Change Filters: Adhere to a filter replacement schedule, typically every 3 to 6 months to ensure proper airflow.
  • Conduct Terminal Tightness Checks: Perform thorough checks of all electrical connections at least twice a year to prevent wiring issues attributable to loose connections.
  • If substantial wiring or sensor issues arise or if you are not equipped with the proper tools, ensure a certified HVAC technician is called to perform the repairs.

For basic operator checks, visual inspections of filters and prodding for airflow at the supply vents can be obtained without any specialized training.

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