I recently hooked up an IC fan. I used a 170* temp. switch with power coming from the ignition wire. I noticed that when the fan was running and I shut the car down, there would be a slight delay before the engine stopped, and the valve behind the SC would snap shut with a sucking sound... Something to do with power feedback from the fan until it wound down and stopped. It didn't seem to be harmful, but I didn't care for it...
I am going to reconnect it to to be powered soley by the ACC wire (and remove the 170* switch) so it will run continuously when the car is on...