If you can access the fan either from the inside or roof give it
a little spin. Maybe you can stick a long slender screwdriver
thru a louver or something.
With the AC OFF, give the fan a spin.
It might just be stuck.
If it seems stuck and you get it moving and that cures it,
then you'll need to disassemble enough to oil the shaft.
Use engine oil. Just a couple drops. WD40 might work
for a short time but it'll evaporate in a few weeks.
Engine oil will last a couple years if you can manage to get it
on the shaft bearings.
It's doubtful the motor actually has an oil hole but maybe....
It's also possible the run capacitor has taken a dump.
These are not expensive.
Check for a stuck fan motor first.
If the fan is not stuck but it hums and trys to turn, it's probably
a bad capacitor.
This is more likely a shop job but I've changed the one on my
home AC. But I've got 37 years of industrial maintenance under
Let us know what you find.