To ensure that any installed air handling unit [AHU] is well-maintained, operates efficiently, and continues to meet design requirements even years after installation, it should be inspected, tested, and maintained at the following intervals:

  • Weekly
  • Monthly
  • 6 months
  • 12 months
  • 24 months
  • 36 months

There are 8 key reasons to conduct regular maintenance. Not having a simple, detailed, and regular maintenance program can significantly affect the operation, failures/wear and tear, and energy usage of the unit:

  • Higher failure rates of equipment and components, increasing overall costs and maintenance/repair requirements.
  • Higher operating costs as the fan motor works harder to push air through unmaintained filters and coils.
  • Coils cannot function at peak efficiency, operational conditions, and performance specifications.
  • Additional complaints from building occupants due to affected comfort levels caused by filters, coils, controls, and valves not working as designed.
  • Odors and general indoor air quality issues due to dirty filters, coils, and drainage pans.
  • Damage to existing installations, such as ceilings and walls being soiled by airborne dirt particles, often visible as dirty streaks.
  • Fire risk due to the accumulation of potential flammable materials inside the ductwork.
  • Early detection and resolution of issues help maintain a more efficient system.

The following article will cover a typical preventive maintenance regime for the AHU and some of its associated equipment.

🟩 Who Will Complete the Inspections and Maintenance?

If the building is still under construction or within the defect liability period, the general/main contractor will be responsible for the maintenance.
If the building/system is beyond the defect liability period, the maintenance will be completed by the building facility manager/operator.

🟩 Parts and Components to be Inspected:

  • Air Inlet and Plenum
  • General Ductwork
  • Attenuators
  • AHU Frame and Casing
  • Dampers
  • Mixing Box
  • Filters
  • Frost Coils
  • Blower Fan and Direct Drive Motor
  • Vibration Mounts
  • Electrical Isolators
  • Emergency Stop
  • DX System Compressor
  • DX System Evaporator
  • DX Condenser
  • CHW Cooling Coil
  • Condensate Tray and Drainage System
  • LTHW Heating Coil
  • Electric Heater
  • Steam Generator
  • Humidifier
  • Heat Exchanger/Thermal Wheel
  • Pumps
  • Control Valves
  • Actuators
  • Pressure Sensors
  • Temperature Sensors
  • Thermostats
  • CO2 Sensor
  • Smoke Detector
  • Variable Speed Drive
  • AHU Control Panel
  • Air Terminal Devices
  • External DX Unit

🟩 Routine Maintenance Program:

Routine inspections and timing will be divided according to the following intervals/schedule:

  • Weekly inspections
  • Monthly inspections
  • Quarterly inspections (every 3 months)
  • Semi-annual inspections (every 6 months)
  • Annual inspections (every 12 months)
  • Biennial inspections (every 24 months)
  • Triennial inspections (every 36 months)

🟩 Weekly Inspection Checklist:

Task Type

  • W-1 Inspect the unit: Observe and inspect the unit for any changes in operating conditions. Investigate further if any are noted.
  • W-2 Inspect the unit: Listen for unusual noises. Investigate further if any are noted.
  • W-3 Inspect the setpoint: Visually check the temperature setting to ensure it meets design/operational needs. Investigate the cause and reset if no reason is provided. Changes may impact the building’s energy use.
  • W-4 Inspect the steam generator: Check for damage and leaks.
  • W-5 Inspect the steam humidifier: Check for any damage or leaks.
  • W-6 Inspect the steam humidifier: Visually check water levels.
  • W-7 Inspect the steam humidifier: Visually inspect the general steam installation and supply pipes for any damage or leaks.
  • W-8 Inspect the steam humidifier: Visually inspect the drain pipes for blockages and clogs.
  • W-9 Inspect the steam humidifier control panel: Visually inspect electrical connections, components, and wires for damage/issues.

🟩 Monthly Inspection Checklist:

Task Type

  • 1M-1 Inspect filters: Visually inspect the filter for dust, debris, foreign objects, moisture, and odors. Replace if it smells or contains moisture.
  • 1M-2 Inspect filters: Visually inspect the filter frames and rails for contamination, foreign objects, corrosion, and damage. Clean or inspect/perform corrective action if anything is noted.
  • 1A-3 Inspect filters: Take readings from differential pressure devices/BMS on the filters. Replace or clean if the maximum pressure difference is exceeded.
  • 1A-4 Inspect strainer: Remove the strainer mesh and check for contamination, foreign objects, corrosion, and damage. Clean or inspect/perform corrective action if anything is noted.
  • 1A-5 Measure steam humidifier: Take samples and analyze the water quality and conductivity servicing the steam equipment to ensure it meets the manufacturer’s requirements. Investigate any issues and take corrective measures.

🟩 Quarterly (3-month) Inspection Checklist:

Task Type

  • 3M-1 Inspect the unit: Visually inspect the internal and external cleanliness of the unit. Perform corrective actions if anything is noted.
  • 3M-2 Inspect fan motor: Check belts and pulleys for tension and wear in accordance with the manufacturer’s requirements. Investigate any issues and take corrective measures.
  • 3M-3 Inspect fan motor: Inspect motor bearings for vibration, noise, overheating, and lubrication. Perform corrective action/lubrication if necessary.
  • 3M-4 Measure chilled water: Take samples and analyze the water quality servicing all wet coils to ensure it meets the original design requirements. Investigate any issues and take corrective measures.
  • 3M-5 Measure heating water: Take samples and analyze the water quality servicing all wet batteries to ensure it meets the original design requirements. Investigate any issues and take corrective measures.
  • 3M-6 Inspect frost coil: Visually inspect for contamination, foreign objects, corrosion, leaks, and damage. Clean or inspect/perform corrective action if anything is noted.
  • 3M-7 Inspect cooling coil: Visually inspect for contamination, foreign objects, corrosion, leaks, and damage. Clean or inspect/perform corrective action if anything is noted.
  • 3M-8 Inspect evaporator: Visually inspect for contamination, foreign objects, corrosion, leaks, and damage. Clean or inspect/perform corrective action if anything is noted.
  • 3M-9 Inspect evaporator: Visually inspect for any ice formation. Perform corrective action if anything is noted.
  • 3M-10 Inspect condenser: Visually inspect for contamination, foreign objects, corrosion, leaks, and damage. Clean or inspect/perform corrective action if anything is noted.
  • 3M-11 Inspect compressor: Check oil levels to ensure they meet the manufacturer’s requirements. Perform corrective action if anything is noted.
  • 3M-12 Inspect condensate drain: Visually inspect the tray for contamination, foreign objects, corrosion, and damage. Clean or inspect/perform corrective action if anything is noted.
  • 3M-13 Scale condensate drain tray: Perform a flow test on the drain tray, holder, and piping system. Perform corrective action if anything is noted.
  • 3M-14 Inspect heating coil: Visually inspect for contamination, foreign objects, corrosion, leaks, and damage. Clean or inspect/perform corrective action if anything is noted.
  • 3M-15 Inspect thermal wheel: Visually inspect for contamination, foreign objects, corrosion, and damage. Clean or inspect/perform corrective action if anything is noted.
  • 3M-16 Inspect thermal wheel: Visually inspect all seals for contamination, foreign objects, corrosion, damage, and wear and tear. Clean or replace if any issues are noted.
  • 3M-17 Inspect thermal wheel: Check bearing clearance, lateral movement, or imbalance. Perform corrective action if anything is noted.
  • 3M-18 Inspect thermal wheel: Inspect motor bearings for vibration, noise, overheating, and lubrication. Perform corrective action/lubrication if necessary.
  • 3M-19 Inspect thermal wheel: Inspect belts and pulleys for tension and wear in accordance with the manufacturer’s requirements. Investigate any issues and take corrective measures.
  • 3M-20 Inspect thermal wheel: Visually inspect motor connections for wear and tear/issues. Perform corrective action if necessary.
  • 3M-21 Inspect thermal wheel: Inspect the drive components of the unit. Perform corrective action if anything is noted.
  • 3M-22 Inspect thermal wheel condensate drain: Visually inspect the tray for contamination, foreign objects, corrosion, and damage. Clean or inspect/perform corrective action if anything is noted.
  • 3M-23 Scale thermal wheel condensate drain tray: Perform a flow test on the drain tray, holder, and piping system. Perform corrective action if anything is noted.
  • 3M-24 Scale thermal wheel: Test the heat exchanger to ensure it rotates and functions in accordance with the manufacturer’s requirements. Perform corrective action if anything is noted.
  • 3M-25 Inspect steam humidifier: Visually inspect the general operation of the equipment, including the spray head, pumps, control panel, and drainage. Perform corrective action if anything is noted.

🟩 Semi-Annual (6-month) Inspection Checklist:

Task Type

  • 6M-1 Scale filters: Measure the pressure difference across all filters in the unit using a calibrated device, cross-referenced with the BMS. Adjust the setpoint if a difference is noted. Replace or clean if the maximum pressure difference is exceeded.
  • 6M-2 Inspect attenuator: Visually inspect the inside and outside for contamination, foreign objects, corrosion, damage, and wear and tear. Perform corrective action if anything is noted.
  • 6M-3 Inspect air mixing box: Visually inspect for contamination, foreign objects, corrosion, damage, and wear and tear. Perform corrective action if anything is noted.
  • 6M-4 Scale air mixing box: Move damper blades to ensure they do not stick, get damaged, or move incorrectly. Perform corrective action if anything is noted.
  • 6A-5 Inspect air mixing box: Inspect damper bearings and connections for issues. Perform corrective action if anything is noted.
  • 6M-6 Inspect fan blades: Manually turn the fan to check for obstructions or issues. Perform corrective action if anything is noted.
  • 6M-7 Inspect fan motor: Visually inspect motor mounts and brackets for torque and wear and tear in accordance with the manufacturer’s requirements. Perform corrective action if necessary.
  • 6M-8 Inspect fan motor: Check the alignment of the motor and shafts. Perform corrective action if necessary.
  • 6M-9 Inspect fan blades: Check for misalignment, imbalance, vibration, contamination, foreign objects, corrosion, and damage. Perform corrective action if necessary.
  • 6M-10 Inspect equipotential bonding: Inspect the unit, parts, and components for bonding. Perform corrective action if anything is noted.
  • 6M-11 Inspect compressor: Visually inspect connections and vibration components. Perform corrective action if necessary.
  • 6M-12 Inspect electric heater: Visually inspect for contamination, foreign objects, corrosion, and damage. Clean or inspect/perform corrective action if anything is noted.
  • 6M-13 Scale electric heater: Test the operation and function of the heater to ensure it works in accordance with the design and manufacturer’s requirements. Perform corrective action if necessary.
  • 6M-14 Inspect steam humidifier: Drain the steam cylinder and clean the lime trap.
  • 6A-15 Inspect control valves: Visually inspect to ensure they are free of damage, contamination, or rust. Perform corrective action if necessary.
  • 6M-16 Inspect actuators: Visually inspect to ensure they are connected, and free of damage, contamination, or corrosion, including cables and connections. Perform corrective action if necessary.
  • 6M-17 Inspect temperature sensors: Visually inspect to ensure they are clean, free of damage, rust, or contamination, including cables. Perform corrective action if necessary.
  • 6A-18 Inspect humidity sensors: Visually inspect to ensure they are clean, free of damage, rust, or contamination, including cables. Perform corrective action if necessary.
  • 6A-19 Inspect pressure sensors: Visually inspect to ensure they are clean, free of damage, rust, or contamination, including cables. Perform corrective action if necessary.
  • 6M-20 Inspect thyristors: Visually inspect to ensure they are clean, free of damage, rust, or contamination, including cables. Perform corrective action if necessary.
  • 6M-21 Inspect smoke detector: Visually inspect to ensure it is clean, undamaged, unworn, or free of contamination. Perform corrective action if necessary.
  • 6M-22 Inspect time clock: Visually inspect the unit’s time clock settings to ensure they are aligned with the design intent. Perform corrective action if necessary.
  • 6M-23 Inspect control panel: Visually inspect the interior and exterior, including cable connections, to ensure they are clean, undamaged, and free of wear and tear or contamination. Perform corrective action if necessary.
  • 6M-24 Scale control panel: Perform a lamp test to ensure they are lit. Perform corrective action if necessary.
  • 6M-25 Inspect fresh air duct: Visually inspect to ensure it is free and clear and that the flexible connection to the plenum/grille is in good condition. Perform corrective action if necessary.
  • 6M-26 Inspect fresh air duct insulation: Visually inspect for damage, tears, and unaffected vapor barriers. Perform corrective action if necessary.
  • 6M-27 Inspect recirculation air duct: Visually inspect to ensure it is free and clear and that the flexible connection to the unit is in good condition. Perform corrective action if necessary.
  • 6M-28 Inspect recirculation air duct insulation: Visually inspect for damage, tears, and unaffected vapor barriers. Perform corrective action if necessary.
  • 6M-29 Inspect supply air duct: Visually inspect to ensure it is free and clear and that the flexible connection to the unit is in good condition. Perform corrective action if necessary.
  • 6M-30 Inspect supply air duct insulation: Visually inspect for damage, tears, and unaffected vapor barriers. Perform corrective action if necessary.

🟩 Annual (12-month) Inspection Checklist:

Task Type

  • 12M-1 Inspect inlet grille: Visually inspect for contamination, foreign objects, corrosion, and damage. Perform corrective action if necessary.
  • 12M-2 Inspect exhaust grille: Visually inspect for contamination, foreign objects, corrosion, and damage. Perform corrective action if necessary.
  • 12M-3 Inspect unit: Visually inspect all screws and bolts to ensure they are tight and secure.
  • 12M-4 Inspect unit door seals: Visually inspect for contamination, foreign objects, corrosion, damage, and leaks. Perform corrective action if necessary.
  • 12M-5 Inspect unit section seals: Visually inspect for contamination, foreign objects, corrosion, damage, and leaks. Perform corrective action if necessary.
  • 12M-6 Inspect unit casing: Visually inspect for moisture or condensation buildup. Perform corrective action if necessary.
  • 12M-7 Replace fan motor: Replace all belts. Perform corrective action if necessary.
  • 12M-8 Inspect fan motor: Visually inspect electrical connections and torque settings. Perform corrective action if necessary.
  • 12M-9 Scale fan motor: Measure the current drawn from the motor during operation and compare it with the equipment manufacturer’s datasheet. Perform corrective action if necessary.
  • 12M-10 Scale emergency stop: Test the emergency stop button and its operation. Perform corrective action if necessary.
  • 12M-11 Scale safety switches: Test all safety switches and shut down devices. Perform corrective action if necessary.
  • 12M-13 Inspect fan blades: Clean the fan, blades, and impeller, remove rust on the shaft, and recoat if necessary.
  • 12M-14 Inspect fan blades: Adjust the fan if it rubs.
  • 12M-15 Replace filters: Replace 1st stage filters if not previously done.
  • 12M-16 Scale filters: Measure the pressure difference across all filters in the unit using a calibrated device, cross-referenced with the BMS. Adjust the setpoint if a difference is noted. Replace or clean if the maximum pressure difference is exceeded.
  • 12M-17 Inspect frost coil: Test the coil flow rate with a calibrated device to ensure it meets system design requirements and cross-reference with the BMS where appropriate. Investigate and take corrective action if anything is noted.
  • 12M-18 Inspect cooling coil: Test the coil flow rate with a calibrated device to ensure it meets system design requirements and cross-reference with the BMS where appropriate. Investigate and take corrective action if anything is noted.
  • 12M-19 Inspect heating coil: Test the coil flow rate with a calibrated device to ensure it meets system design requirements and cross-reference with the BMS where appropriate. Investigate and take corrective action if anything is noted.
  • 12M-20 Inspect compressor: Check the rotary lock valves to ensure they move freely. Investigate and take corrective action if anything is noted.
  • 12M-21 Inspect compressor: Visually inspect the condition of the oil sump heater. Investigate and take corrective action if anything is noted.
  • 12M-22 Inspect compressor: Check the manifold pipes and connections. Investigate and take corrective action if anything is noted.
  • 12M-23 Scale compressor: Test the operation of the high-pressure sensor. Investigate and take corrective action if anything is noted.
  • 12M-24 Scale compressor: Test the operation of the low-pressure sensor. Investigate and take corrective action if anything is noted.
  • 12M-25 Scale compressor: Measure the current and power consumption during operation and compare it with the equipment manufacturer’s datasheet. Investigate and take corrective action if anything is noted.
  • 12M-26 Inspect compressor: Check refrigerant charge and oil levels. Investigate and take corrective action if anything is noted.
  • 12M-27 Scale evaporator: Test the function of the expansion valve. Investigate and take corrective action if anything is noted.
  • 12M-28 Scale condenser: Test the function of the expansion valve. Investigate and take corrective action if anything is noted.
  • 12M-29 Inspect cooling system: Check the condition of the safety valve. Investigate and take corrective action if anything is noted.
  • 12M-30 Inspect refrigerant system: Check for refrigerant leaks from pipes and connection points. Investigate and take corrective action if anything is noted.
  • 12M-31 Inspect steam humidifier: Inspect and clean the steam cylinder. Investigate and take corrective action if anything is noted.
  • 12M-32 Inspect steam humidifier: Check and clean the humidifier. Investigate and take corrective action if anything is noted.
  • 12M-33 Scale actuators: Inspect and test the function, measure input signals, and check operating and set ranges. Investigate and take corrective action if anything is noted.
  • 12M-34 Scale temperature sensors: Check calibration with a calibrated device and cross-reference each sensor with the BMS/controls. Investigate and take corrective action if anything is noted.
  • 12M-35 Scale humidity sensors: Check the calibration of each sensor, cross-referencing with a calibrated device and the BMS/controls. Investigate and take corrective action if anything is noted.
  • 12M-36 Scale pressure sensors: Check the calibration of each sensor with a calibrated device, cross-referencing with the BMS/controls. Investigate and take corrective action if anything is noted.
  • 12M-37 Scale freeze protection thermostat: Check calibration and function with a calibrated device and cross-reference the sensor with the BMS/controls. Investigate and take corrective action if anything is noted.
  • 12M-38 Scale CO2: Check calibration and function with a calibrated device and cross-reference the sensor with the BMS/controls. Investigate and take corrective action if anything is noted.
  • 12M-39 Scale smoke detector: Test and ensure it functions according to the design. Investigate and take corrective action if anything is noted.
  • 12M-40 Inspect variable speed drive: Check that operation and settings conform to the design, cross-referenced with the BMS/controls. Investigate and take corrective action if anything is noted.
  • 12M-41 Inspect electrical isolators: Test the function of all isolators [On/Off]. Investigate and take corrective action if anything is noted.
  • 12M-42 Inspect control panel: Visually check cable glands and terminals to ensure they are secure. Investigate and take corrective action if anything is noted.
  • 12M-43 Inspect control panel: Check to ensure the wiring diagram is available near or inside the panel. Investigate and take corrective action if anything is noted.
  • 12M-44 Inspect control panel: Visually inspect to ensure all protective covers are installed. Investigate and take corrective action if anything is noted.
  • 12M-45 Inspect control panel: Test the function of all switches to ensure they work as required. Investigate and take corrective action if anything is noted.
  • 12M-46 Scale control panel: Test the control functions of the unit to ensure they operate according to the design intent. Investigate and take corrective action if anything is noted.
  • 12M-47 Inspect fresh air duct: Visually inspect two locations along the internal surfaces of the duct for contamination, moisture, condensation, foreign objects, corrosion, and damage. Add other areas, investigate, and perform corrective actions as necessary.
  • 12M-48 Inspect supply air duct: Visually inspect two locations along the internal surfaces of the duct for contamination, moisture, condensation, foreign objects, corrosion, and damage. Add other areas, investigate, and perform corrective actions as necessary.
  • 12M-49 Inspect return air duct: Visually inspect two locations along the internal surfaces of the duct for contamination, moisture, condensation, foreign objects, corrosion, and damage. Add other areas, investigate, and perform corrective actions as necessary.
  • 12M-50 Inspect grilles and diffusers: Clean the terminal devices.

🟩 Biennial (24-month) Inspection Checklist:

Task Type

  • 24M-1 Replace filters: Replace 2nd stage filters if not previously done.
  • 24M-2 Scale fire dampers: Test fire dampers on fresh air, recirculation air, and supply air to ensure they function according to the design.
  • 24M-3 Inspect hygiene: Check the AHU for hygienic cleaning [if humidifier installed].

🟩 Triennial (36-month) Inspection Checklist:

Task Type

  • 36M-1 Inspect hygiene: Check the AHU for hygienic cleaning [if no humidifier installed].

This concludes the preventive maintenance guide for the AHU.