Blower Motor Operation

The Automatic Temperature Control (ATC) front and rear blower control provides continuously variable control of air flow rate to meet occupant comfort requirements. Pulse width modulation of the blower motor power allows the front and rear blower to operate at any speed from off to full speed. When front or rear blower operation is required, the ATC sends a PCI Bus message to the Front Control Module (FCM) requesting blower relay ON. The FCM provides a ground for the front and rear blower motor relay coils, activating both relays. The front and rear blower relays provide 12 volts to their respective blower motor power modules. Each module provides a 12-volt blower motor control signal to the ATC. The ATC provides a pulse width modulated (duty-cycle) ground signal to this circuit based on climate requirements. The higher voltage on the signal circuit (less duty-cycle ground) the lower the blower speed request. The lower voltage on the signal circuit (more duty-cycle ground) the higher the blower speed request.