For 1990-2009 cars

The air delivery controls are divided into the following 5 areas:

1. HVAC control components
2. Air speed
3. Air distribution
4. Recirculation operation
5. 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 control module communicates on the low-speed data bus. 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, then all HVAC DTCs and settings will be erased from KAM. The temperature display reading at the control head can be converted from °C to °F by pressing the Auto button for a minimum of 3 seconds. The ignition 3 voltage circuit provides a device on signal. The control module supports the following features:

Feature | Availability
--- | ---
Afterblow | dealer turn-on feature
Purge | Yes
Personalization | No
Actuator Calibration | Yes

#### Mode/Recirculation Actuator

The mode and recirculation actuators are XXX-wire bi-directional electric motors that incorporate a feedback potentiometer. Low reference, XXX-volt reference, position signal, and 2 control circuits enable the actuators to operate. To coordinate the actuators movement the control circuits use either a 0 or 12-volt value. Both control circuits have a value of 0 volts when the actuator is at rest. 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 XXX-XXX volts.

#### Mode Valve Assembly

The film valve system has several operating characteristics:

• | The cycle time for a mode change will vary based on the starting point of the film valve relative to the requested mode position.

• | Recalibration will typically occur when the engine is OFF. The actuator noise heard during recalibration may be more noticeable than during normal operation.

• | The amount of air rush noise heard when a mode change is requested that causes the film valve to move through 3 or more primary modes is dependent on blower speed.

• | The maximum time to achieve a mode change occur when the film valve travels between vent and defrost.

• | Mode change times may very slightly based on variations in system airflow, temperature and voltage.

#### 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 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 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.

To operate the following conditions must be met:

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

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

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

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

• | The mode valve moves to the floor position.

• | The recirculation door moves to outside air position.

• | The blower will run for XXX seconds (XXX minutes XXX seconds) at 68 percent blower speed.

#### Air Distribution

The mode actuator is controlled by the HVAC control module 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 switch is moved to the bi-level through defrost positions, the A/C compressor clutch engages and the recirculation actuator will be moved to the outside air position. When VENT is pressed, the following will occur:

• | The mode valve will be moved to the panel position.

• | The recirculation actuator will follow user request if blower is on and power mode is in run.

• | The A/C compressor will follow user request if blower is on and power mode is in run.

#### Recirculation Operation

The HVAC control module controls the air intake through the recirculation actuator. Recirculation is not available when the mode is in bi-level through defrost. The operator must activate the blower for Recirculation operation.

### 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.

The following is required to place the HVAC system in automatic mode:

• | The blower motor switch must be in the AUTO position.

• | The air temperature switch must be in any other position other than 60 or 90 degrees.

• | The mode switch must be in the AUTO position.

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

• | Request A/C operation

• | Position the mode actuator

• | Position the recirculation actuator

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 blower will stay on high and the air temperature actuators will stay in the full cold position when the coldest position is selected in automatic operation.

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.

### Remote Vehicle Start HVAC Operation

The HVAC preset RVS settings are as follows:

• | Inside air temperature input below XXX°C (XXX°F) the HVAC system will set the blower motor speed to high speed, set the mode door to the defrost position, set the temperature door to the full hot position and set the recirculation door to the outside air position.

• | Inside air temperature input above XXX°C (XXX°F) the HVAC system will set the blower motor speed to high speed, set the mode door to the panel position, set the temperature door to the full cold position, request A/C compressor operation and set the recirculation door to the recirculate position.

• | Inside air temperature input between XXX°C (XXX°F) and XXX°C (XXX°F) the HVAC system will set the blower motor speed to a medium speed, set the mode door to the panel position, set the temperature door to the full cold position, request A/C compressor operation and set the recirculation door to the outside air position.

The C68 control head reverts to the prior remote start function settings when you transition from remote start to normal operation by entering car, inserting key and turning on.