AHU Maintenance Checklist: Air Handling Unit Guide

Daily Checks

• Check supply and return air temperatures — compare to setpoint
• Listen for unusual noise from the fan or motor
• Check for visible air leaks at the AHU casing and duct connections
• Verify the condensate drain is flowing (during cooling operation)
• Check the control panel for alarms or fault indicators

Monthly Maintenance

• Check and replace air filters — measure pressure drop; replace at manufacturer's recommended differential (typically 250 Pa)
• Inspect the cooling and heating coils for dirt and biofouling — clean if necessary
• Check the fan belt for tension and condition — adjust or replace
• Inspect the fan and motor bearings — listen with an ultrasonic stethoscope
• Check the condensate drain pan — clean if dirty, verify the drain is not blocked
• Inspect the dampers — verify they move freely and position correctly
• Check the motor amperage — compare to nameplate FLA
• Inspect the AHU casing for air leaks — seal with appropriate gasket or sealant
• Clean the temperature and humidity sensors — dust on sensors causes inaccurate readings

Annual Maintenance

1. Replace all air filters: Use the correct filter class (G4, F7, F9, etc.) for the application. Consider upgrading to higher-efficiency filters if air quality is an issue.
2. Deep clean the coils: Use a coil cleaner and low-pressure water. Clean both the air side and the water/refrigerant side (if accessible). Brush the fins straight if bent.
3. Service the fan: Check the impeller for dirt buildup and balance. Inspect the housing for corrosion. Lubricate bearings (if not sealed). Check the belt condition and alignment.
4. Service the motor: Check bearings, winding resistance (megger test), and wiring connections. Verify the motor cooling fan is clean.
5. Inspect and service dampers: Clean and lubricate the damper linkages. Verify the actuator operates smoothly. Check the damper blades for damage and seal degradation.
6. Clean the condensate system: Remove and clean the condensate drain pan. Flush the drain line. Check the trap for proper operation.
7. Calibrate sensors: Calibrate the temperature, humidity, and pressure sensors against a reference instrument.
8. Inspect the casing and insulation: Check for air leaks, damaged insulation, and corrosion. Seal leaks and repair insulation.
9. Check the control system: Verify all control sequences operate correctly — start/stop, temperature control, damper control, safety interlocks.
10. Performance test: Measure the supply airflow, temperature, and static pressure. Compare to design values and previous year's readings.

Common Problems