Inspect the unit casing for chips corrosion. If damage is found, clean and repaint.
Clean the fan wheels. Remove any rust from the shaft with an emery cloth and recoat with L.P.S. 3 or equivalent.
Inspect and clean drain pans.
Check damper linkages, fan set screws, and blade adjustment. Clean, but do not lubricate, the nylon damper rod bushings.
Clean damper operators.
Inspect, clean, and tighten all electrical connections and wiring.
Rotate the fan wheel and check for obstructions. The wheel should not rub. Adjust the center if necessary.
Examine flex connections for cracks or leaks. Repair or replace damaged material.
Source: MaintainX (Community Member)