Blower Control

Blower motor speed is controlled by the solid state blower control module, which follows commands from the HVAC programmer. The HVAC programmer, in turn, determines the proper blower speed using information from the heater and A/C control and its network of sensors.

The HVAC 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 (Buick) or nine (Oldsmobile) 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 HVAC programmer's network of sensors. Sensors that provide information that may affect blower speed in AUTO mode include:

- In-vehicle temperature sensor.
- Outside temperature sensor.
- Solar sensors.
- Engine coolant temperature sensor.
- Vehicle speed sensor.