Fan works OK in positions 1-2, 6-8 with engine running? Check for ACC unit DTCs with Tech II. ACC generates DTCs if requested fan speed ≠ indicated speed from the fan control. If fan control failure is flagged, replace it.
I have an 05 Linear with manual controls that go up to 5 (knob). I swapped out the unit, and I had the same problem. No real change in the motor speed after 3. 3, 4 and 5 run the motor at the same speed.
Thanks for clarifying. 2007 is last MY with MCC. MCC pin 27 sends 0-5V to fan control pin 2 to select fan speed. If this voltage is being sent correctly and fan power supply is good, fan control or fan motor is the culprit.