/22Important Notes:The air tubes are identified for placement as follows:Front to back: Tube No. 1 67 Holes of .156” diameterTube No. 2 67 Holes of .140” diameterTube No. 3 67 Holes of .140” diameterTube No. 4 67 Holes of .125” diameterFigure 4.3 – Secondary Air Tube replacement4.6 Fan Maintenance & CareClean the fan air inlet louvres and squirrel cage impeller regularly. The fan should be kept clean anddust free. Life of the fan will be shortened if operated in a dust filled environment, or if the fan isoverheated by restricting air supply. Stalling the rotor, or over firing the insert with the fan turned offwill also damage the fan. The fan must not be overheated. Do not disassemble the fan. "ALTERING