This an example of how the external fan system can keep the internal fans of the Canon C500 from turning on even at high temperatures. This test was done for me, but also recorded to share. I left the DSLRs internal record on auto and felt the auto record was not an accurate portrayal of the fan noise as it raised an lowered to find the sound, because of this I left the video silent and you can look at the camera screen to see the fan icons trigger. You can also look at the thermometer to see the near by temperature. I have audio sample of fan noise on my blog!
If you want more information feel free to read my blog about the fan noise issue.