The blower motor for heat/AC stays on high unless you select the ‘auto lo’ switch. In addition it will continue to run when the ignition switch is turned to the off position – sometimes. Has anyone else experienced this phenomena?
Is this vehicle still under warranty? If it is, it doesn’t matter whether you are the only person who experienced this phenomenon, or if every Pacifica owner has that problem. Just take it back for free repair.
If it is not under warranty, I would first suspect the resistor that controls the various speeds of the blower motor.
I suspect that your system has a continuously variable speed control rather than the normal speed control resistors that just provide a few speeds. If that is correct then most likely the trouble is with the solid state speed controller. The output to the motor has shorted internally to the power supply. You will need to replace the unit. Follow the wires from the motor and they should lead you to the unit.
It may be the Front Blower Motor relay, in the Integrated Power Module, may be sticking closed.