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If you put in bad URLs for your pools you can fire up a unit and the fans will run, albeit at a somewhat lower speed, without hashing.
I use a similar technique in reverse to cool my Antminers before shutting them down. Specifically, I change the pool URLs to something wrong (by adding an 'x' character to the domain, for example) then hit "Save & Apply". The result is the miner software restarts, but can't get work from any pools, so the fans run without the boards doing any real work. After a few minutes the output from the fans is significantly cooler.
I have to admit that I don't know if cooling them down before powering them off provides any actual value. But with the insane amount of BTUs these suckers pump out it feels like just shutting them off while hot is not a great idea.
Me likey that trick! Methinks I will add that as a custom command sequence in
Awesome Miner for when I do have to turn them off for cleaning and such.

Yes you are right, simple powering down does result in a rather significant temp spike in the miners for at least a minute or more.