Help troubleshooting Early 2009 Mac Pro (2x 2.66 GHz Quad Core) Fan Issues I have an early 2009 Mac Pro (2 x 2.66 GHz Quad Core) that recently started having issues.  It started as the black screen issue, that I troubleshooted to find that there was an issue with the CPU tray.  I found this out by doing the usual troubleshooting, replacing the graphics card and then buying a used second machine and interchanging the CPU cards between chassis.
I ended up replacing the 2009 Octocore CPU tray with an Early 2009 2.8GHz Quad core tray, as this machine has now become a spare machine, but the fans are cranking loudly.
When I run hardware diagnostics I see that the PS, Exhaust and Intake fans are not running and the PCI and Boosta fans are running at 850 rpm - seemingly not too far above min spec.
I would love to get guidance as to how to get the three fans running again and got my lovely mac pro back to its usual quiet self.  The loud noise is unbearable in my home office.
Thanks for the guidance.
After some research I discovered that the fans were blowing because I put a single CPU tray into a machine that originally had a dual CPU tray.  Apparently it doesn't like this mismatch and runs the fans full, as it thinks it has suffered failure of a CPU.