For 1990-2009 cars

The Air Delivery Description and Operation is divided into 5 primary areas:

• | HVAC Control Components

• | Air Speed

• | Air Speed Auxiliary

• | Air Distribution

• | Recirculation

• | Automatic 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 air temperature and distribution settings. The battery positive voltage circuit provides power that the control module uses for keep alive memory (KAM). The instrument panel module (IPM), which is the vehicle power mode master, provides a device on signal. The control module supports the following features:

Function | Availability
--- | ---
Afterblow | Yes
Purge | Yes
Personalization | Yes
Actuator Calibration | No
Heated Seat Control | Optional

The HVAC control module will receive information that defines the current driver of the vehicle from driver door module (DDM) through class 2 communication. The HVAC system will memorize the following system configurations for up to 2 unique drivers:

• | Driver set temperature

• | Passenger set temperature

• | Mode

• | Blower motor speed

• | A/C compressor request, auto ON or A/C OFF

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 or key On, the last stored settings for the current driver will be activated, except the settings for the rear defrost and heated seat.

#### 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 volt. 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 mode actuator is a 5-wire bi-directional electric motor that incorporates a feedback potentiometer. Ignition 3 voltage, low reference, control, 5-volt reference and position signal circuit enable the actuator to operate. The control circuits use either a 0 or 2.5-volt value to command the actuator movement. When the actuator is at rest, control circuits have a value of 2.5-volts. 0-5 volts control signal commands actuator move to the opposite direction. When the actuator shaft rotates, the potentiometers 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.

### Air Speed

The blower motor forces air to circulate within the vehicle 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, turn on 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:

1. The blower motor will RUN for 20 seconds.
2. The blower motor will be OFF for 10 minutes.
3. The blower motor will RUN for and additional 20 seconds.

### Air Distribution

The HVAC control module controls the mode actuator in order to distribute airflow to a desired outlet. The mode switch 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.

Important: The HVAC system allows air to the outboard panel outlets in all air distribution modes. This allows air to be circulated higher in the cabin under any operating condition. The panel outlets have three operating positions, open, side window defogger and closed. To eliminate air from these outlets, the individual outlet thumbwheel must be turned to the OFF or side window defogger position.

### Recirculation

The HVAC control module controls the air intake through the recirculation actuator. Recirculation is not available when the mode is in defrost. When the mode is in defog, recirculation will only be available for 10 minutes. In the outside air position, the incoming air is filtered by the passenger compartment air filter.

### Automatic Operation

In automatic operation, the HVAC control module will maintain the comfort level inside of the vehicle by controlling 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.

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:

• | Regulate blower motor speed

• | Position the air temperature actuator

• | Position the mode actuator

• | Position the recirculation actuator

• | Request A/C operation

When the warmest position is selected in automatic operation the blower speed will increase gradually until the vehicle reaches normal operating temperature. 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. The mode actuator will remain in the floor position.

When the coldest position 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 the panel position and the recirculation actuator will remain in the recirculation 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.

### Auxiliary HVAC Control Module

The auxiliary HVAC control module is a non-GMLAN device that interfaces between the operator and the auxiliary HVAC system to maintain air temperature and air distribution settings. Five volts and ground 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 HVAC control module (on which position to place the actuator) on GMLAN bus.

### Auxiliary Air Distribution

The auxiliary HVAC control module provides airflow direction and temperature control for the back seat passengers. Passengers can operate the rear HVAC control module in both manual or automatic modes. Auxiliary HVAC mode positions can be set to OFF, VENT, FLOOR and VENT, or FLOOR positions. The front HVAC module provides power and ground to the auxiliary mode actuator. The front HVAC module receives power through the ignition 1 and battery positive voltage circuits from the underhood fuse block. The auxiliary mode actuator is a reverse polarity motor. Each circuit provides both power and ground to the auxiliary mode actuator. When the auxiliary mode actuator is being held in position, both of the auxiliary mode door control circuits have 0 volt applied to both sides of the actuator motor. This holds the actuator stationary. When a mode is selected, one of the auxiliary mode door control circuits will ground, driving the auxiliary mode actuator to the desired temperature. Depending on the mode that is requested, the other auxiliary air temperature door control circuit may ground. This moves the auxiliary mode actuator into the desired position.

### 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 volt. 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.