HVAC Blower Controls Circuit Description

The solid state [1][2]blower control module controls the blower motor speed. The solid state blower control module follows commands from the heater and A/C programmer. The heater and A/C programmer determine the proper blower speed using information from the following components:
^ The heater and A/C control
^ The network of sensors

In order to determine the appropriate output voltage, the [1][2]blower control module monitors a pulse width modulated voltage signal from the heater and the A/C programmer. The module amplifies the signal and applies voltage directly to the blower motor. The heater and A/C programmer monitors the blower control module output voltage. The blower control module outputs a voltage that carries between 0 volts (blower motor OFF) and 12 volts (maximum blower motor speed). The blower control module is located near the blower motor. The blower control module is mounted to the side the Heating, Ventilation, And Air Conditioning (HVAC) module.

The blower operates in either of the following modes:
^ The MANUAL fan mode
^ The AUTO fan mode

In the MANUAL fan mode, 6 (Buick) or 9 (Oldsmobile) different fan speeds are available. Once a tan speed is selected, the desired fan speed remains constant until a new speed is selected from the heater and A/C control.

In the AUTO fan mode, the blower speed is infinitely variable (between minimum and maximum speeds) and varies automatically according to the conditions monitored by the heater and A/C programmer's network of sensors. The following sensors provide information that may affect blower speed in the AUTO mode:
^ The inside temperature sensor
^ The ambient temperature sensor
^ The sun load sensors
^ The engine coolant temperature sensor
^ The vehicle speed sensor