DXP6800 Pro PSU Fan Change

I exchanged the fan of the PSU with a Noctua NF-A4x20 fan. When restarting the NAS, the PSU fan does not come on. How can I test that the PSU fan is working fine? Does it only come on under heated conditions? I am currently copying some files between the drives to try to generate some load..

Since one has to modify the connector of the Noctua fan to fit the DXP6800 PSU pin plug (3 to 2), it's not impossible that I broke the fan.