S90 almost over heated...!

[precopster]

If you have a Android device and a ELM-327 you can monitor the coolant temp and see it go up to 105deg C at which point the fan will come on. You could rev it at constant 2,000 rpm and it should come on at around 2 mins but be careful as the temp guage should't even rise at this temp. If the temp guage starts to creep above halfway you may want to replace the coolant temp sensor which is on the thermostat housing.

[jimmy57]

S90 will have a high pressure sensor read by the ECM. ECM will run the fan on low or high as indicated by a/c high side pressure.
If it is 25 or warmer and you let it stand idling with a/c on then the fan should run within a minute or less due to a/c pressure.
If it is not cooling because there is no refrigerant in system then the pressure will not build enough to trigger fan.
Engine temp causing fan to come on is as described above.

The wires were secure in the grey connector? I have seen non functioning fans because the gray plug snapped in place but the wires were not slid onto the bullet terminals of the relay.