For 1990-2009 cars

Battery voltage is supplied to the Blower Control Module through circuit 1342. This power supply is used by the Blower Control Module to feed the blower motor, 4 to 12 volts depending on the blower speed setting. The Blower Motor Control Module, and blower motor are grounded through circuit 150. The HVAC Control Assembly sends the selected blower speed setting to the Blower Control Module through circuit 63. The blower speed signal is a 12 volt pulse width signal, increased on time indicates a higher blower speed setting.