For 1990-2009 cars

The air delivery description and operation is divided into 4 areas:

• | HVAC control components

• | Air speed

• | Auxiliary air speed

• | Air delivery

• | Auxiliary air delivery

• | Recirculation operation

### HVAC Control Components

#### HVAC Control Module

The HVAC control module is a non-class 2 device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The battery positive and ignition 1 voltage circuits provide power to the control module. The control module supports the following features:

Feature | Availability
--- | ---
After Blow | Yes
Purge | Yes
Personalization | Yes
Actuator Calibration | Yes

#### Auxiliary HVAC Control Module (part of rear seat audio controls)

The auxiliary HVAC control module is located as an integral part of the rear seat audio controls located in the rear center console. The system can be controlled from both the front and rear controls. To activate the rear hvac system press the AUX button on the front climate controls, an indicator will be lit. Pressing the AUX button once will set the rear hvac into mimic mode. In this mode the airflow in the rear will be approximately the same direction, temperature, and fan speed as the front. Pressing the front climate control AUX button again will turn the rear system and the indicator off. If the rear controls are adjusted, the rear control will enter a rear independent state. Airflow in the rear will then be according to the settings of the rear hvac controls. The rear system can be turned off by pressing the AUX button on the front HVAC climate control and the status light will turn off. If the front AUX button is off then the rear climate control system is off. A GM LAN device that interfaces between the rear seat occupants and the auxiliary HVAC system to maintain auxiliary air temperature and auxiliary air distribution settings. The battery positive voltage circuit provides power that the control module uses for keep alive memory (KAM). If the battery positive voltage circuit loses power, all auxiliary HVAC DTCs and settings will be erased from KAM. The auxiliary HVAC control module will perform a recalibration of the electric actuators when commanded with a scan tool or if KAM is lost. This will ensure the actuators are moving with in the calibrated range. During this calbration process the auxiliary blower motor will be disabled for up to 3 minutes. With this hvac control head a automatic operation can be achieved by pressing the plus or minus temperature buttons to increase or decrease cabin temperature. The temp display on the rear hvac head will display the temp setting increasing or decreasing. These climate control functions will only display in rear independent mode when the rear controls are being used. Manual controls of the rear climate control consist of: Fan to decrease or increase fan speed. The up arrow fan control will turn on the rear hvac control in manual mode. The down arrow fan control will turn off the rear hvac manual mode. The increase and decrease temperature buttons adjust the rear flow of air temperature to the rear occupants. The mode button will manually change the direction of air flow in your vehicle. Mutiple presses will cycle through the rear air delivery selections until the desired mode of choice is displayed.

#### Auxiliary HVAC Control Module (three knobs located in rear headliner)

This type of rear climate control consists of three knobs located in the rear headliner. This rear control system can be controlled form both the front and rear hvac. To turn on this rear system, press the front HVAC controls AUX button, an indicator on the AUX button will be lit. To activate the rear hvac system press the AUX button on the front climate controls, an indicator will be lit. Pressing the AUX button once will set the rear hvac into mimic mode. In this mode the airflow in the rear will be approximately the same direction, temperature, and fan speed as the front. Pressing the front climate control AUX button again will turn the rear system and the indicator off. If the rear controls are adjusted, the rear control will enter a rear independent state. Airflow in the rear will then be according to the settings of the rear hvac controls. The rear system can be turned off by pressing the AUX button on the front HVAC climate control and the status light will turn off. If the front AUX button is off then the rear climate control system is off. The three rear control knobs starting from the left, fan control turning clockwise or counter clockwise. Turning the fan control knob all the way counter clockwise turns the rear climate control off. Center knob controls the rear temperature of the air flowing through the rear passenger compartment. A clockwise turn into the red dial area produces warmer air, a counter clockwise turn into the blue dial area produces cooler airtemperatures. The right knob controls air delivery with choices of VENT air directed through headliner outlets. Bi-Level air is delivered through the floor outlets as well as the headliner outlets. Floor air is directed through floor outlets, the location of the floor outlets is directly behind the second row seats.

#### 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 circuit uses 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 potentiometer's adjustable contact changes the door position signal between 0-5 volts.

#### Auxiliary Mode Actuator

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 two 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 auxiliary HVAC control module grounds one of the control circuits while providing the other with 12 volts. The control module reverses the polarity of the control circuits to move the actuator in the opposite direction. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door position signal between 0-5 volts.

The auxiliary 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 grounds both control circuits.

#### 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, battery positive 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 processor supplies 12 volts to the blower motor through the blower motor voltage supply circuit. The control processor uses the blower motor ground or low reference as a low side control to adjust the blower motor speed.

#### Air 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. The blower motor will only operate if the blower motor switch is in any position other than OFF, and the ignition switch is in the RUN position.

Once a blower speed is selected, the blower speed remains constant until a new speed is selected.

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 microbial growth that can create undesireable odors. The vehicle does not come with the afterblow feature enabled. If the afterblow feature is required due to an odor concern, it must be turned on by the scan tool. Certain items need to have happened for afterblow to operate:

• | The A/C compressor operated on the latest key cycle.

• | The system voltage is at least 11 volts to start and 10 volts to continue to run.

• | The ignition has been in the OFF position for at least 30 minutes.

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

• | The blower will run for roughly 2 minutes.

• | The recirculation door moves to the outside air position.

• | The mode valve moves to the floor position.

### Air Delivery

The mode actuator controls air delivery. The HVAC control module controls the actuator in order to distribute airflow to a desired outlet. When the vehicle operator selects the defrost, mix-blend or floor positions, the A/C compressor clutch engages and the recirculation actuator will be moved to the outside air position. The flow of air during the various modes of operation is as follows:

• | Panel--Outside Air and Recirculation inlet air setting, full air from Instrument Panel (I/P) outlets

• | Bi-Level--I/P and front and rear floor outlets

• | Floor--Small amount of air to the right and left side window outlets and a larger amount of air to the Front and Rear floor outlets

• | Mix-Blend--Floor and defroster outlets with a slight bleed to the I/P outlets

• | Defrost--Defrost outlets with a small amount of air to the right and left side window outlets and to the Driver Side floor outlet and a very small amount to the Rear floor outlet

### Recirculation Operation

The recirculation 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 actuators 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 potentiometer's adjustable contact changes the door position signal between 0-5 volts.