So I had the fan control unit replaced ($160 part, my labor), the problem still exist.
So far, I have tested by unplug the sensor on top of the thermostat, the fan runs, at low speed. Unplug the sensor on top of the AC valve, the fan stop, and when I plug it back, the fan runs, at low speed. On both case, the fan runs for couple min, then stops, then runs again.... If I apply 12v to the fan, it runs at high speed. Replaced the fan control unit, nothing change.
I measure the voltage that the fan receives when it runs, and I saw it goes from 5.4v then slowly drop to zero (corespond to the fan go from slow to stop). Never had I saw it goes beyond 6v. This explain why the fan run at low speed.
Is there anything I need to look at ?