Blower Speed Control

Blower motor speed is controlled by the pulse width modulated blower control module, which follows commands from the heater and A/C programmer. The heater and A/C programmer, determines the proper blower speed using the requested information from the heater and A/C control assembly and the information provided by its network of sensors.

The heater and A/C programmer's blower speed command to the blower control module is a pulse width modulated voltage. The blower control module outputs about 4 volts to run the blower motor at its slowest speed, and battery voltage to run at maximum speed.

The blower can be operated in either manual fan mode or AUTO fan mode. In manual fan mode, six different fan speeds are available and, once selected, fan speed remains constant until a new speed is selected from the heater and A/C control.

In AUTO fan mode, blower speed is infinitely variable (between minimum and maximum speeds) and varies automatically according to conditions monitored by the heater and A/C programmer's network of sensors. Sensors that provide information that may affect blower speed in AUTO mode include:

^ Inside air temperature sensor.
^ Ambient air temperature sensor.
^ Sun load sensors.
^ Engine coolant temperature sensor.
^ Vehicle speed sensor.

The blower control module is attached to the HVAC module and is located near the blower motor.