The body cotrol module has an output on it that allows it to set the blower to full speed. I don't know under what circumstances this is activated.
You can try disconnecting the control head connector. Just pop out the controls (the knobs) and unplug the connector in the back. If the fan still goes full tilt I'd say the BCM is telling it to do so. If it shuts off, I'd say you have a bad speed control switch.
As a curiosity, what setting is the vent/ac knob in? Is it on an AC setting or windshield defrost? Try turning it to the floor or panel vents to see if that makes a difference.
Last edited by lametec; 05-05-2009 at 12:50 PM.