HVAC Blower Controls Circuit Description

Blower motor speed is determined by the voltage applied to the blower motor. This voltage varies from approximately 4V (low speed) to approximately 12V (high speed). The voltage applied to the blower motor is controlled by the blower motor control module. The blower motor speed can be adjusted manually by pressing the fan up or down switches or automatically by placing the heater-a/c control in the AUTO mode. The heater-a/c control sends blower request information to the blower motor control module in the form of a variable voltage signal. This voltage signal ranges from approximately 0.5V (for low speed) to approximately 7V (for high speed). An amplifier and driver circuit in the blower motor module supplies voltage (4-12V) to the blower motor according to the request signal from the heater-a/c control.