The Air Delivery Description and Operation is divided into 6 primary areas:

HVAC Control Module

The HVAC control module is a GMLAN device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The battery positive voltage circuit provides power that the HVAC control module uses for keep alive memory (KAM). The body control module (BCM), which is the vehicle power mode master, provides a device on signal. The control module supports the following features:

Remote Start and Personalization

When the Remote Start feature is activated through the key FOB, it starts up the vehicles automatic HVAC control system according to the previous settings of the system before turning the vehicle off. When the outside temperature is cold, the automatic HVAC control system will start up the rear window defogger and if the vehicle has heated seats, they will also turn on. Cooled seat are activated during a remote start. Normal operation of the automatic HVAC control system will return after the key is turned to RUN position.

If the remote start personalization feature for climate control is selected through radio, the HVAC control module will receive information that defines the current driver of the vehicle from the Remote Keyless Entry via GMLAN. This information shall be stored inside the HVAC control module memory. When a different key fob is selected, the HVAC control module will recall the appropriate driver settings. When the HVAC control module is first turned ON, the last stored settings for the current driver will be activated. Upon a battery reset, the HVAC control module shall also set the driver ID to Driver#2. The HVAC system will memorize the following system configurations for up to 2 unique drivers:

OnStar® Blower Control ON/OFF

During OnStar® audio control ON, the HVAC control module receives signals from OnStar® to reduce blower speed level. When OnStar® audio control is active, the blower control runs the fan at a reduced speed to enable audio communications. This ensures that all incoming and outgoing voice calls will be recognized by the OnStar® module. The driver is allowed to override the OnStar® auto blower level by increasing or decreasing it manually to any desired level. When OnStar® no longer sends the request for blower control the HVAC control module will cancel OnStar® blower control and resume previous blower level if no manual override of the blower was selected.

Mode Actuator

The mode actuator is a 5-wire bi-directional electric motor that incorporates a feedback potentiometer. Low reference, 5-volt reference, position signal, and 2 control circuits enable the actuator to operate. The control circuits use either a 0 or 12-volt value to coordinate the actuator movement. When the actuator is at rest, both control circuits have a value of 0 volts. In order to move the actuator, the HVAC control module grounds one of the control circuits while providing the other with 12 volts. The HVAC control module reverses the polarity of the control circuits to move the actuator in the opposite direction. When the actuator shaft rotates, the potentiometers adjustable contact changes the door position signal between 0-5 volts. The HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted value, one of the control circuits is grounded. As the actuator shaft rotates, the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module removes power and ground from the control circuits.

Recirculation Actuator

The recirculation actuators are 5-wire bi-directional electric motors that incorporate a feedback potentiometer. Ignition 3 voltage, low reference, control, 5-volt reference and position signal circuits enable the actuators to operate. The control circuit uses either a 0, 2.5, or 5-volt signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 volts. A 0 or 5-volt control signal commands the actuator movement in opposite directions. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door position signal between 0-5 volts.

Blower Motor Relay

The blower motor relay provides a supply voltage to the blower motor and blower motor control processor. The HVAC control module commands the blower motor relay ON anytime the commanded blower speed is not OFF.

Blower Motor Control Processor

The blower motor control processor is an interface between the HVAC control module and the blower motor. The blower motor speed control, blower motor supply voltage and ground circuits enable the control processor to operate. The HVAC control module provides a pulse width modulation (PWM) signal to the control processor in order to command the blower motor speed. The 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 knob dial in a desired speed position or by selecting automatic operation. In manual operation, the blower has six speed selections. The HVAC control module may alter the blower motor speed due to compensating factors. In automatic operation, the HVAC control module will determine what blower speed is necessary in order to achieve or maintain a desired temperature. In manual and automatic operation, the blower speed temporarily reduces speed during transition between outlet modes.

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

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

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. Refer to Service Programming System (SPS).

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

Once the above conditions have been met, the following sequence of events will occur:

1. The blower motor will RUN for 20 seconds.
2. The blower motor will be OFF for 10 minutes.
3. The blower will repeat step 1 and 2 above for 2 more cycles.

The HVAC control module controls the mode actuator in order to distribute airflow to a desired outlet. The mode knob provides the vehicle operator with the ability to override the automatic setting. When the mode door is moved to the defrost position, the A/C compressor clutch engages and the recirculation actuator will be moved to the outside air position. In the outside air position, the incoming air is filtered by the passenger compartment air filter.

The HVAC control module controls the air intake through the recirculation actuator. Recirculation is not available when the mode is in defrost or defog. When the mode is in floor, recirculation will only be available for 3 minutes. If the system is in full (100%) recirculation continuously for more than 20 minutes, the recirculation actuator moves to a 95% recirculation door position. The HVAC control module will prevent the system from returning to the full recirculation position until the next ignition cycle. In the outside air position, the incoming air is filtered by the passenger compartment air filter.

In automatic operation, the HVAC control module will maintain the comfort level inside of the vehicle by requesting the A/C compressor clutch, the blower motor, the air temperature actuators, mode actuator and recirculation.

To place the HVAC system in full automatic operation, the AUTO selection must be activated on both knobs.

Once the desired temperature is reached, the blower motor, mode, recirculation and temperature actuators will automatically adjust to maintain the temperature selected. The HVAC control module performs the following functions to maintain the desired air temperature:

When the warmest setting 90°F is selected in automatic operation, the blower speed will increase gradually to the maximum speed. Temperature actuators will be in full heat position, mode actuators will be in floor position while maintaining 90°F temperature setting. When normal operating temperature is reached, the blower will stay on high speed and the air temperature actuators will stay in the full heat position.

When the coldest setting 60°F is selected in automatic operation, the blower will stay on high and the air temperature actuators will stay in the full cold position. The mode actuator will remain in panel position and the recirculation actuator will remain in RECIRC position.

In cold temperatures, the automatic HVAC system will provide heat in the most efficient manner. The vehicle operator can select an extreme temperature setting, but the system will not warm the vehicle any faster. In warm temperatures, the automatic HVAC system will also provide air conditioning in the most efficient manner. Selecting an extreme cool temperature will not cool the vehicle any faster.

The auxiliary HVAC control module is a GMLAN device that interfaces between the operator, the front HVAC control module, and the auxiliary HVAC system to maintain air temperature and air distribution settings. Battery power, ground, and LED dimming are supplied to the rear HVAC control module. The front HVAC control module monitors the position of the rear air temperature actuator and the rear mode actuator. The front HVAC module will move the actuators to the proper position when it receives a request from the rear HVAC control module on which position to place the actuator. The rear HVAC control module is powered ON or OFF through GMLAN communication of vehicle power-mode.

The rear control can be turned ON and OFF by pressing the AUX button on the front HVAC control module. The rear control can also be turned ON by pressing any rocker button on the control head. Pressing the fan blower rocker button down will eventually turn off the control head. When the front climate control system is turned off or in defrost mode, the rear climate control system is turned off. The rear system will turn back on once another front mode is selected.

The auxiliary mode actuator is a 5-wire bi-directional electric motor that incorporates a feedback potentiometer. Low reference, 5-volt reference, position signal, and 2 control circuits enable the actuator to operate. The control circuits use either a 0 or 12-volt value to coordinate the actuator movement. When the actuator is at rest, both control circuits have a value of 0 volts. In order to move the actuator, the HVAC control module grounds one of the control circuits while providing the other with 12 volts. The HVAC control module reverses the polarity of the control circuits to move the actuator in the opposite direction. When the actuator shaft rotates, the potentiometers adjustable contact changes the door position signal between 0-5 volts. The HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted value, one of the control circuits is grounded. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module removes power and ground from the control circuits.