After a factory reset "auto (off/low/high)" is set by default.
As described, the fan spins up at start up, stops, spins up somewhere at 43° C and keeps spinning, not regarding lower temperature (32°C).
For an "active" setting of this option I set the fan to "auto (low/high)". After saving, the fan starts immediately spinning. By the way if you kill the "fancontrol" process before saving the fan control setting, the process is restarted afterwards. This holds also for the hibernating setting (--> "fancontrol" is also responsible for hibernating the plates).
Finally I set the fan back to "auto (off/low/high)" followed by the same behavior as for "auto (low/high)".
By the way, it's quite annoying, waiting for the NAS to heat and cool down...
In "/sbin" is a file called "fan.script". The script explains the start up behavior:
#temperature w 1 43
#sleep 1
#temperature w 2 47
#sleep 1
fanspeed s
sleep 1
fanspeed l
sleep 5
fanspeed g > /tmp/fan_status
Calling "temperature g 1" returns 167° F (75° C). Look's like the configured temperatures are independent of the "temperature" settings.