Air handling unit quarterly preventive maintenance plan

Tasks at each service

1. 1

   Check the filters and replace those at their final pressure drop

   Read the differential pressure across each filter stage and replace the filters that have reached the final pressure drop given by the filter manufacturer, or that are damaged or wet. Check that the frames seal with no bypass.

   Measurement20 min

   Tools: Differential pressure gauge

2. 2

   Inspect the fan, its belts and its pulleys

   Check the impeller for dirt and damage, the belts for cracks, glazing and tension, and the pulley alignment. Replace worn belts as a matched set. On a direct-drive fan, check the motor mounts and the impeller fixing.

   Inspection20 min

   Risks: Isolate and lock out the fan, and wait for it to stop completely, before opening the fan section.

3. 3

   Measure the fan motor current

   Measure the running current of the fan motor and compare it with the nameplate and the previous readings; a drop can reveal a slipping belt or a closed damper.

   Measurement10 min

   Tools: Clamp meter

4. 4

   Inspect the heating and cooling coils

   Look for dirt on the face of the coils, flattened fins, corrosion and leaks at the headers and valves. Straighten bent fins with a fin comb.

   Inspection15 min

   Tools: Fin comb

   Risks: Stop and isolate the fan before opening the access doors or reaching inside the unit.

5. 5

   Clean the condensate pan and check the drain

   Remove sludge and slime from the drain pan, check that it drains completely with no standing water, and that the trap is filled and the drain line is clear. Standing water in an air handling unit is a source of microbial growth.

   Action15 min

   Risks: Stop and isolate the fan before opening the access doors or reaching inside the unit.

6. 6

   Check the dampers and their actuators

   Drive each damper through its full stroke from the controls and check that the blades open and close fully and the linkages are tight.

   Verification10 min
7. 7

   Inspect the casing, the doors and the insulation

   Check that the access doors close and seal, the inside of the unit is clean and dry, and the internal insulation is intact and not shedding fibres.

   Inspection10 min

   Risks: Stop and isolate the fan before opening the access doors or reaching inside the unit.

8. 8

   Grease the fan and motor bearings (regreasable bearings only)

   Apply the grease type and quantity given by the manufacturer; never over-grease. Skip bearings sealed for life.

   Action15 minoptionalonce every 2 services

   Tools: Grease gun

9. 9

   Clean the coils

   Clean both faces of the coils with a low-pressure water spray or a coil cleaner suited to the fin material, rinsing towards the drain pan, then check that the pan drains.

   Action60 minonce every 4 services

   Risks: Isolate the fan and protect the motor and electrical parts from water.

10. 10

    Test the frost protection

    Simulate a low temperature at the frost thermostat or sensor and check that the unit reacts as designed (fan stop, outdoor damper closed, heating valve open) and raises its alarm.

    Verification15 minonce every 4 services
11. 11

    Restart and record the readings

    Restart the unit, check the supply air temperature and the absence of abnormal noise, then record every value in the work order.

    Verification5 min