HVAC Blower Controls Circuit Description C60

The blower motor is a variable speed motor. The higher the voltage applied to the motor, the faster the speed.

Voltage is supplied to the blower motor by the heater-A/C control through the blower motor resistor. At low and medium speeds (I, II and III, IIII), the voltage is stepped down by the internal blower motor resistors. Each internal resistor also has a thermal limiter in series with it. At high speed (IIIII), the internal blower motor relay is energized, removing the internal blower motor resistors from the circuit. Voltage is then applied directly to the blower motor through the relay, thus the blower motor runs at maximum speed.

HVAC Blower Controls Circuit Description CJ4

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. The front or rear HVAC control assembly 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 front or rear HVAC control assembly.