Air Handling Unit (AHU) Maintenance Schedule – Australia
1. Monthly Tasks (Every 1 Month)
Designed for standard commercial sites. Increase frequency for hospitals or critical operations.
Air Filters
Inspect pre-filters and fine filters for dust loading.
Replace if pressure drop exceeds manufacturer limits.
Record differential pressure across filter banks.
Fan, Belts & Motor Assembly
Inspect belt tension and alignment.
Check fan bearings for noise, heat, and vibration.
Verify motor amperage against nameplate.
Inspect fan scroll and impeller for debris accumulation.
Coils & Heat Exchangers
Check coil face for dirt buildup.
Inspect for corrosion and refrigerant/hydronic leaks.
Verify correct airflow temperatures and ∆T.
Condensate Drain & Trays
Inspect drains for blockages.
Check traps are primed.
Clean trays and ensure proper slope.
Sensors & Actuators
Check temperature, humidity, and pressure sensors for correct readings.
Confirm damper actuators (OA, RA, EA) respond correctly to BMS commands.
General Visual Inspection
Inspect casing integrity, insulation, and door seals.
Check for unusual noise, vibration, or smells.
Confirm all AHU access doors close securely (required by AS/NZS 3666).
2. Quarterly Tasks (Every 3 Months)
Recommended for most Australian commercial buildings.
Filters
Replace pre-filters (typical 3-month cycles).
Inspect HEPA/MERV/secondary filters (change as required).
Fans
Check pulley alignment, set screws, and belt wear.
Lubricate bearings if not sealed type.
Coils
Temperature performance check (supply/return air).
Inspect for mould or biological growth (AS/NZS 3666 compliance).
Dampers
Test damper travel and verify the OA minimum position is set correctly.
Lubricate moving components.
BMS Functional Test
Verify all I/O points.
Test alarms (filter DP, fan proof, damper faults, high/low temp).
Confirm correct operation under occupied/unoccupied modes.
3. Six-Monthly Tasks (Every 6 Months)
Mandatory for AS/NZS 3666 microbial compliance.
Microbial (Hygiene) Inspection
Conduct hygiene inspection of coils, pans, and air paths.
Inspect for mould, slime, and microbial contamination.
Swab testing if required for sensitive sites.
Cleaning Scope
Clean coils using AHU-approved coil cleaning chemicals.
Clean drip trays, drains, and insulation surfaces.
Clean fan blades and internal AHU sections.
Mechanical Checks
Check motor mounts and fan alignment.
Inspect flexible duct connectors.
Inspect vibration isolators.
Fire & Smoke Control
Test smoke/fire dampers where connected to AHU.
Verify shutdown and purge modes if BMS controlled.
4. Annual Tasks (Every 12 Months)
Deep Cleaning
Full internal AHU chamber clean.
Coil deep clean (fin combing if required).
Replace secondary filters (if not done earlier).
Mechanical Overhaul
Replace belts regardless of visual condition (best practice).
Replace fan bearings if noisy or worn.
Perform motor insulation resistance testing.
Performance Testing
Measure airflows (L/s or m³/s).
Verify fan speeds, static pressure, and design compliance.
Check chilled water/hot water valve performance.
BMS Review
Full control loop tuning (supply air temperature, static pressure).
Review energy-saving strategies (economy cycle, VSD optimisation).
Ensure trend logs and alarms are operational.
Asset & Compliance Documentation
Update service records.
AS/NZS 3666 compliance sign-off.
Record filter changes, microbial inspections, and airflow readings.
Optional Add-Ons for Critical Sites (Hospitals, Data Centres, Pharma)
Monthly
HEPA filter DP logging.
Redundancy checks for duty/standby fans.
Space pressure validation (positive/negative rooms).
Quarterly
Validate supply air conditions for infection control spaces.
Calibrate critical sensors (temperature, humidity, differential pressure).
Annually
HEPA filter integrity testing (DOP/PAO test).
Vibration analysis of motors and fans.
