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2 Case Fans Running at Different RPMs

Hi, i have a question about these 2 case fans that i just installed: http://www.gelidsolutions.com/products/index.php?lid=1&cid=2&id=35

The case fan in the front is plugged into the PWR_FAN 3-pin slot and is running at around 1,500 RPM (that is the ideal speed)

The case fan in the back is plugged into the CHA_FAN 3-pin slot, but is running at only around 1,000 RPM.

They're both running without the fan speed controller that came with them, but i've also ran both with the fan speed controller set to max and received the same results - the front fan is running at a higher RPM than the back fan.

I downloaded AMD OverDrive and it indicates that both fans are running at 100%, so i was wondering if anyone knows why the back fan is running slower than the front one?

Thank you.

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My current setup:

AMD Phenom II X4 955 Black Edition Deneb 3.2GHz Socket AM3 125W
ASUS M4A785TD-V EVO AM3 AMD 785G
G.SKILL 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10600) F3-10600CL8D-4GBHK
Western Digital Caviar Blue WD5000AAKS 500GB 7200 RPM SATA
XFX PVT98GYDLU GeForce 9800 GT 512MB 256-bit GDDR3 PCI Express 2.0 x16
Antec Basiq 500W PSU
Microsoft Windows 7 Home Premium 64-bit
4 answers Last reply Best Answer
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  1. Best answer
    Sure they are the same model, if so, swap them round and see what happens, could be a feature of your bios.

    If the speeds stay the same with rear now at 1500rpm, keep them that way, you "should" create negative air pressure by sucking more air out that you intake, for best airflow.
  2. Ok, I'll do that tomorrow when i have time. Thanks also for the negative air flow advice.
  3. das_stig said:
    Sure they are the same model, if so, swap them round and see what happens, could be a feature of your bios.

    If the speeds stay the same with rear now at 1500rpm, keep them that way, you "should" create negative air pressure by sucking more air out that you intake, for best airflow.



    Yup, it was a BIOS feature. I had smart fan enabled and it was setup to power the 2 fans at different RPMs. If i disable smart fan, both fans will run at max RPM.
  4. Best answer selected by foggydj.
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