For 1990-2009 cars

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

• | HVAC Control Components

• | Air Speed

• | Air Delivery

• | Recirculation Operation

### HVAC Control Components

#### HVAC Control Module

The HVAC control module is a GMLAN device that interfaces between the operator and the HVAC system to maintain desired air temperature and 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 HVAC DTCs and settings will be erased from KAM. The body control module (BCM), which is the vehicle mode master, provides a device on signal. The HVAC control module provides blower, air delivery mode, air temperature settings and input signals to auxiliary HVAC control module. The HVAC system assembly receives power from battery input with ignition 3 voltage circuit as a backup.

The HVAC control module supports the following features:

Feature | Availability
--- | ---
Afterblow | Yes
Purge | No
Personalization | Yes
Actuator Calibration | Yes

#### Auxiliary HVAC Control Module (without RSA)

The Auxiliary HVAC Control Module uses a set of three potentiometers to control rear fan speed, temperature, and mode settings. The Auxiliary HVAC Control module has inputs for 5V and low Reference that is used by all three potentiometers. There are three signal circuits between each of the potentiometers and the HVAC Control Module.

#### Auxiliary HVAC Control Module (with RSA)

Auxiliary HVAC Control functions are integrated into the Rear Seat Entertainment Module. The Rear Seat Entertainment Module communicates Rear HVAC settings over serial data.

#### Auxiliary HVAC Control Functions

All Auxiliary functions and DTCs are handled by the HVAC control module. There are two ways the rear functions can be controlled.

Control from the HVAC control module: If the AUX button on the HVAC control module is pressed, the rear HVAC system will be enabled. The settings for the rear will mimic the Driver settings on the HVAC Control Module.

Control from the auxiliary HVAC control module: If at any time any of the three Auxiliary controls are adjusted, control of the rear HVAC System will transfer to the Auxiliary controls. If the Aux button is not currently enabled, adjusting the Auxiliary controls will enable it, even if the front system is Off.

#### Front 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.

#### 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 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.

### Air Speed

#### Front Blower Motor Control Processor

The front blower motor control processor is an interface between front HVAC control module and front blower motor. The front blower control processor regulates supply voltage and ground circuits to front blower motor. The front HVAC control module provides a blower speed signal to the control processor in order to command the desired 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 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:

1. The HVAC control module decreases the amount of time that the blower motor speed control circuit is modulated to ground.
2. 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 the scan tool.

The following conditions must be met for afterblow to operate:

• | The A/C compressor operated during the prior 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 a range of 2 minutes 30 seconds to 4 minutes.

• | The recirculation door moves to outside air position.

• | The mode valve moves to the floor position.

#### 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.

### Air Delivery

#### Front Control

The HVAC control module controls the distribution of air by the use of recirculation and mode actuators. The modes that may be selected are:

• | Defrost

• | Defog

• | Panel

• | BI-Level

• | Floor

The mode actuator is connected to the mode door by a cam type linkage system. Depending on the position of the door, air is directed through the HVAC module and distributed through various ducts leading to the outlets in the dash. If a fault is detected within the mode door travel, the HVAC control module will drive the actuator to defrost, which is a default position for the mode door actuator. Turning the mode door position to either defrost or defog positions, the HVAC control module will move the recirculation actuator to outside air reducing window fogging. When defrost/defog is selected, the A/C compressor is activated. The A/C compressor clutch will engage when ambient temperatures are above 3°C (38°F). A/C is available in all modes. Recirculation is only available in Panel and Bi-Level modes. The rear window defogger does not affect the HVAC system.

#### Auxiliary Control

The auxiliary HVAC system provides ventilation for the rear seat occupants. The rear seat occupants will exercise control of the auxiliary air delivery modes, air speed and the air temperature setting. The HVAC control module will have the ability to override the auxiliary HVAC control module by placing it in any position other than auxiliary.

The auxiliary mode switch in the HVAC control module allows the driver to direct the air flow in the rear of the vehicle between the floor, headliner, or a blend between the 2 options. Power is provided to both front and auxiliary HVAC control modules from I/P fuse block on the ignition 3 voltage circuit.

### Recirculation Operation

The HVAC control module controls the air intake through the recirculation actuator. The recirculation switch closes the recirculation door in order to circulate the air within the vehicle. The outside air switch opens the recirculation door in order to route outside air into the vehicle. Regardless of the blower motor switch position, recirculation is available only in the Panel and Bi-Level mode switch positions. The mode switch must be placed in either the Panel or Bi-Level position before the blower motor switch is placed in the OFF position. When Defrost or Defog positions are selected outside air is circulated to the windshield to reduce fogging. If the recirculation switch is pressed into the ON position when the mode switch is in an unavailable mode position, then the recirculation switch LED will flash 3 times.

### Dual Zone Operation

The HVAC control module uses dual temperature button switches. The dual zone controls allows for maximum temperature offset between and comfort between the driver and passenger. It is possible to select maximum airflow over the evaporator core with one dual zone switch along with maximum airflow over the heater core with the other dual zone switch. Each air temperature actuator is independent from the other and the passenger side is not limited in it's range of temperature offset.

### Remote Start

#### Remote Start Activation

The following describes the HVAC control head functionality upon receiving the remote start active serial data message and a power mode status is set to off/awake. During remote start on the manual HVAC system the blower motor, mode doors, temperature doors, recirc door and A/C request will be set to the current setting on the control panel when the vehicle was last turned off. The rear defrost will be activated and the heated seats will be disabled.

#### Remote Start De-activation

When the remote start is exited, GMLAN power mode equals run mode or remote start engine. In the case of manual settings, the displays will revert to the actual state of operation of the features, on the basis of their normal control algorithms.