AHU Maintenance Checklist: Filters, Coils, Fans, Drain Pans and Controls

Safety Before Inspection

Before carrying out any inspection or maintenance on an AHU, isolate the electrical supply and follow the approved lockout/tagout procedure. Confirm that the fan has stopped completely before opening any access door. Wear appropriate personal protective equipment, including respiratory protection if the filters are heavily loaded. All maintenance activities must be carried out by authorised personnel following the approved site safety procedure and the manufacturer's operation and maintenance manual.

Daily or Routine Observations

During normal operation, observe the AHU for unusual noise, vibration or odour. Check the BMS or local control panel for fault alarms, filter pressure differential readings and supply air temperature and humidity. Confirm that the condensate drain is flowing freely. Note any observations in the maintenance log.

Monthly Checks

Inspect the filter pressure differential readings and compare with the baseline values recorded at commissioning. A rising differential indicates filter loading. Inspect the condensate drain pan for standing water, biological growth or blockage. Check the drain trap for correct water seal. Inspect the access door seals for damage or deterioration. Check the control panel for any logged faults or alarms.

Quarterly Checks

Inspect the cooling and heating coil fins for fouling, damage or corrosion. Check the coil connections for leaks. Inspect the fan blades for dust accumulation, damage or corrosion. Check the fan shaft bearings for noise or excessive temperature. Inspect the flexible duct connections for damage or deterioration. Check the damper blades and actuators for correct operation. Inspect the casing panels and access doors for damage, corrosion or air leakage.

Seasonal Checks

Before the cooling season, clean the cooling coil and confirm that the chilled water system is charged and operating correctly. Before the heating season, clean the heating coil and confirm that the hot water or steam system is operating correctly. Check the outdoor air damper for correct operation and weathertight sealing when closed.

Filter Inspection and Replacement

Replace filters when the pressure differential reaches the maximum value specified by the filter manufacturer, or at the interval defined in the maintenance schedule — whichever occurs first. Handle used filters carefully to avoid releasing accumulated dust. Dispose of used filters in accordance with the site waste management procedure. After filter replacement, record the date, filter type and pressure differential in the maintenance log.

Coil Cleaning

Coil fins should be cleaned using a soft brush or low-pressure compressed air, working in the direction of the fins to avoid damage. Chemical coil cleaners may be used for heavily fouled coils, following the manufacturer's instructions and ensuring that the cleaning agent is compatible with the coil material. Rinse the coil thoroughly after chemical cleaning. Do not use high-pressure water jets, which can damage the fins.

Fan and Motor Checks

Inspect the fan blades for dust accumulation and clean if necessary. Check the fan shaft for correct alignment. Inspect the motor for signs of overheating, moisture ingress or mechanical damage. Check the motor terminal connections for tightness. Measure and record the motor current and compare with the nameplate value. Lubricate the motor bearings at the interval specified by the motor manufacturer.

Belt and Drive Checks

Where the fan is belt-driven, inspect the belts for wear, cracking or glazing. Check the belt tension and adjust if necessary. Inspect the pulleys for wear and correct alignment. Replace belts in matched sets. After belt replacement, check and adjust the tension after the first few hours of operation.

Drain Pan and Trap Inspection

The drain pan must be clean and free of standing water, biological growth and debris. Clean the drain pan with an approved disinfectant at the interval defined in the maintenance schedule. Check the drain trap for correct water seal depth. A shallow or dry trap will allow AHU casing pressure to push air back through the drain, causing water carry-over or allowing odours to enter the supply air.

Damper Operation

Check that all dampers — fresh air, return air, exhaust and bypass — open and close fully and smoothly. Check the actuator linkages for wear or looseness. Confirm that the damper position feedback signals correspond to the actual damper position. Lubricate the damper blade pivots at the interval specified in the maintenance schedule.

Sensor and Control Checks

Calibrate temperature, humidity and pressure sensors at the interval specified in the maintenance schedule. Compare sensor readings with independent reference instruments. Check the control sequences by simulating fault conditions and confirming that the correct alarms and responses are generated. Update the maintenance log with calibration results.

When Specialist Support Is Required

Some maintenance tasks — HEPA filter integrity testing, coil leak testing, refrigerant handling, high-voltage electrical work — require specialist equipment and trained personnel. These tasks must not be carried out by general maintenance staff without the appropriate qualifications and equipment. Contact Vostok Technologies or the approved service provider for specialist maintenance support.