I'd check to see if power is getting to the fan itself when you turn the switch on. Just have to remove fan and use volt meter.
If getting power the fan may be bad, if no power then it could be fuse or the switch.
One of my fans in the front would intermittently not work. Took it out and check, the bearings were freezing up. I went ahead and replaced both of them thinking if one failed the other was not too far behind. I bought the replacement from National Bus in Atlanta.
2002 Monaco Windsor 38 PKD Cummins ISC 350 8.3L
2005 Jeep Grand Cherokee w/5.7 Hemi