I have a couple of server power supply units, namely HP DPS-1200FB. Those PSUs are working just fine (given their mileage) but the DC fans appear to be wearing out so I decided to replace them.
The original fan installed in those PSUs is a Nidec 40mm DC fan with four wires: GND, +12V, Temp and Rotation control.
When I was ordering replacement fans I explicitly asked for only two wires: GND and +12V because I prefer them to be running at full blast all the time.
When I install the replacement fans, the PSU runs for a couple of seconds and then turns itself off. My guess is it checks the RPM reading on the fan, does not get any data and thinks the fan is malfunctioning.
Is there a way to fool the PSU that it actually has the fan installed even though it only has two wires? I attached a picture of the original fan termination for reference.