Great information.  Thanks for the help.   Thanks, Noble
R240 comes with 3 FANs, and I am trying to add the 4th FAN with same model as the other 3.  The issue is it will spin when power on, but unit didn't recognize it.  I can unplug it and plug back in, but system will not provide any warning like the other 3 fans. I went into HW inventory the unit only recognize 3 FANs but not 4. is there certain setting I need to do to make the unit recognize the additional fan?
Add 4th Fan in POWEREDGE R240