Air Speed

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2011 GMC Yukon XL, 2011 GMC Yukon, 2011 Chevrolet Tahoe, 2011 Chevrolet Suburban, and 2011 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.

Front Blower Motor Control Processor

The blower motor control module is an interface between the HVAC control module and the blower motor. The blower motor speed control, battery positive and ground circuits enable the control module to operate. The HVAC control module provides a variable voltage to the blower motor control module to request the selected blower speed. The blower motor control module provides a pulse width modulation (PWM) signal to the blower motor in order to control the blower motor speed. The module supplies 12 volts to the blower motor through the blower motor voltage supply circuit.

The blower motor forces air to circulate within the vehicle's interior. The vehicle operator determines the blower motors speed by placing the blower motor switch in a desired speed position or by selecting automatic operation. In manual operation, once a blower speed is selected, the blower speed remains constant, until a new speed is selected. In automatic operation, the HVAC control module will determine what blower speed is necessary in order to achieve or maintain a desired temperature.

As the requested blower speed increases, the following conditions occur:

The HVAC control module increases the amount of time that the blower motor speed control circuit is modulated to ground.
The voltage and duty cycle, measured between the blower motor speed control circuit and ground, decrease.

As the requested blower speed decreases, the following conditions occur:

The HVAC control module decreases the amount of time that the blower motor speed control circuit is modulated to ground.
The voltage and duty cycle, measured between the blower motor speed control circuit and ground, increase.

If an OnStar® call is initiated while the blower is in the high speed position the blower speed will be lowered to reduce background noise.

Auxiliary Blower Motor Control Processor

The auxiliary blower motor control processor is an interface between the auxiliary HVAC control module and the rear blower motor. The auxiliary blower motor control processor monitors supply voltage and ground circuits to the rear blower motor. The auxiliary HVAC control module provides a pulse width modulation (PWM) signal to the control processor in order to command the blower motor speed. The auxiliary blower motor control processor uses the blower motor ground as a low side control to adjust the blower motor speed.

The blower motor forces air to circulate within the vehicles interior. The vehicle operator determines the blower motors speed by placing the blower motor switch in a desired speed position or by selecting automatic operation. In manual operation, once a blower speed is selected, the blower speed remains constant, until a new speed is selected. In automatic operation, the HVAC control module will determine what blower speed is necessary in order to achieve or maintain a desired temperature.

As the requested blower speed increases, the following conditions occur:

The HVAC control module increases the amount of time that the blower motor speed control circuit is modulated to ground.
The voltage and duty cycle, measured between the blower motor speed control circuit and ground, decrease.

As the requested blower speed decreases, the following conditions occur:

The HVAC control module decreases the amount of time that the blower motor speed control circuit is modulated to ground.
The voltage and duty cycle, measured between the blower motor speed control circuit and ground, increase.

Afterblow

Afterblow is a feature that dries the evaporator core by operating the blower motor after the engine is turned OFF. This reduces the amount of microbial growth that can create undesirable odors. The vehicle does not come equipped with the afterblow feature turned ON. If the afterblow feature is required due to an odor concern, it must be turned ON by reprogramming the HVAC control module.

After the HVAC control module has been programmed for afterblow, the following conditions must be met for afterblow to operate:

The engine has been turned OFF for at least 30 minutes.
The ambient air temperature is at least 21°C (70°F).
The A/C compressor operated for more than 2 minutes before shut down.
The system voltage is at least 12 volts.

Once the above conditions have been met, the following sequence of events will occur for the front blower motor:

The blower motor will RUN for 5 minutes.
The blower motor will be OFF for 3 minutes.
The blower motor will RUN for and additional 5 minutes.
The blower motor will be OFF for 3 minutes.
The blower motor will RUN for and additional 5 minutes.

Once the above conditions have been met, the following sequence of events will occur for the rear blower motor:

The blower motor will RUN for 10 minutes.
The blower motor will be OFF for 5 minutes.
The blower motor will RUN for and additional 10 minutes.
The blower motor will be OFF for 5 minutes.
The blower motor will RUN for and additional 10 minutes.