Mitsubishi Electric FR-E720-0.1 K Instruction Manual page 258

Useful functions
(5) Cooling fan life display
The cooling fan speed of 50% or less is detected and "FN" is displayed on the operation panel and parameter unit (FR-
PU04/FR-PU07). As an alarm display, Pr. 255 bit2 is turned on and also an alarm is output to the Y90 signal.
REMARKS
When the inverter is mounted with two or more cooling fans, "FN" is displayed with one or more fans with speed of 50% or less.
NOTE
For replacement of each part, contact the nearest Mitsubishi FA center.
256