You can plug a 3 pin fan into a 4 pin header just fine.
Connect 4 pin fan to 3 pin motherboard.
When connected to 3 pin fan headers the fan will run at full speed unless the mainboard supports voltage based speed control.
Please note that 4 pin fans can also be connected to your mainboard s 3 pin fan headers though.
My rig has 2 pairs of 3 pin fans phanteks ph140sp connected to two 4 pin motherboard headers asus z97m plus via basic y splitters and they work and control just fine.
Without the fourth pin connected the fan will just run at full speed.
Pwm fans come with a 4 pin connectors for fully automatic speed control via your mainboard s 4 pin pwm fan headers.
4 pin connectors offer the ability to control fan speed via pulse width modulation.
Two of them are for the cpu and three are for the case fans.
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As far as mounting the.
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Next press down until the fan connector until it is fully connected to the motherboard header.
You can plug a 4 pin pwm fan connector into a 3 pin terminal on the motherboard without any problems.
Speed control options rpm range will vary between fans and motherboards on a 3 pin connection but the fan will spin.