There is a 3 terminal connector behind the brake booster that goes to the blower regulator. It has a heavy black and red wire and a lighter yellow wire. The yellow wire is the control signal for the regulator and varies from about 1 volt (low speed) to about 6 volts (high).
You can check voltages with a voltmeter or unplug the connector and remove the yellow wire and see if blower still is at max.
If you replaced the regulator 2 years ago with a quality replacement and it is gone again, then your blower might be drawing excessive current due to dry bushings or worn brushes and commutator.