GM Service Manual Online
For 1990-2009 cars only

The blower motor controller module contains solid state circuitry. At a given duty cycle, the circuitry utilizes a pulse width voltage signal from the control head. The circuitry returns an inverse pulse width signal to the blower motor.

Blower Control Module Duty Signal

Signal to Blower Motor Controller Module from HVAC Controller

Signal out of Blower Motor Controller Module to Blower

0 - 5% Duty

Off (Short)

6% Duty

High

7% - 94% Duty

Inverse Variable Output

95% Duty

Low

96% - 100% Duty

Off

The control head pulse width signal is based on the following conditions:

    • The temperature set by the user
    • The outside air temperature
    • The in-vehicle temperature
    • The input from the solar sensor

For example, the blower motor control module will adjust the blower accordingly when the following conditions exist:

    • The temperature inside of the vehicle is much colder or hotter than the temperature that the user sets.
    • The user selects the AUTO button.

The blower motor controller module will change the blower from a high speed to a low speed as the temperature inside the vehicle becomes closer to the set temperature.