Read the statement by Michael Teeuw here.
how to connect the fans to a raspbery 4
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 what is the common sense to connect the fans to the case of my raspberry 4? the thumbnail of the fans should be up or down? 
  
 I also have the following diagram, is it preferable to connect the fans directly to the external power supply (5V, 5 A) in order to preserve the raspberry?
  Thank you for your help. 
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 @RIKKO14 all of mine are connected directly to the pi 
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 Ok thanks, I tested with a light, the thumbnail of the fans should be up for mine. 
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 @RIKKO14 sorry what is thumbnail of fan? 
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 a priori, the editing on the 1st photo is good because air comes out, not with the editing of the 1st photo 
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 Thumbnail = the sticker on the fan 
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 whenever I unplug my pi and plug it back in the fan will go crazy and make a loud noise. What I do is unplug it and plug it back in multiple times until it goes back to normal. Anyone know why? 
