Fan 1 must be installed if you have a redundant configuration. If you are only using 1 PSU in a redundant configuration you still need fan 1. If your PSU(s) have orange release levers, indicating they are hot-swap, you need fan 1.
Hello,   I am trying to figure out the minimum number of cooling fans my server should have. my server is PowerEdge R430. my question is when do I need only one cooling fan and when do I need the six fans to be installed?   Regards, Sameh
PowerEdge R430 - cooling fan