Rather than reinstall the fan upside down (as I'd imagine there's a logical reason it's installed a certain way), pull out the fan assembly (it comes out from the back of the panel, the front guard pops out forwards and both heated seat buttons + blanks will need to come out), disconnect from loom and prise apart the fan boddy from the housing. Using a damp cotton bud, clean up all the dust and [expletive deleted] which has built up over the fan blades and spindle over time. Spray the locating points of the spindle, and the point where the fan sits with some form of PTFE or Teflon lubricant. reassemble, connect to loom, cover with tissue and switch ignition on. This'll fling any residue/excess lube. Refit to car - voila, quiet fan.Inspired by this thread in the 9-5 forum, I encourage all 900 and 9-3 owners to share their quick fixes.
I'll start with my top-tip: when your ACC cabin air temperature sensor fan gets noisy, pop it out and replace it upside-down. It'll give you another year or so of quiet motoring .[/b]
just remove acc control unit just lever it out with blunt object then remove ash tray you can then remove the two plastic blanks one on each side then remove sensor by inserting a flat blade screw driver at top or bottom retaining tag and it pops out then clean dust out of fan with a kids art brush oh remeber to see which way the sensor is in dash then replace upside down easy.........I've just done this "repair" myself - seems to have done the trick.
Realistically cannot see any way of doing this other than to take the side panel off, push the sensor unit through the panel, rotate 180 then push it back through
Taking the side panel off it the time consuming bit, but beats a replacement sensor at £50+ plus