The air delivery controls are divided into 2 primary areas. The first, air speed, is dependent upon blower motor speed. The second, air distribution, is related to various single or multiple air outlets.

The blower motor forces air throughout the vehicles interior. The vehicle operator determines the blower motor's speed by toggling the blower motor switch manually or by using the automatic mode. The blower motor will always operate at some speed as long as the HVAC control module is in any position other than OFF, as long as the ignition switch is in the RUN position. The blower motor and mode switches are located within the HVAC control module.

Power is provided to the blower motor from the blower motor control processor through the blower motor supply voltage circuit. The blower motor control processor receives power from the under hood electrical center through the battery positive voltage circuit. Ground is provided by the blower motor control processor and ground circuit.

When any blower speed is selected, whether manual or automatic, the blower motor control processor will control blower motor speeds based on a 5-volt signal circuit that is pulse width modulated (PWM) signal by the HVAC control module. When a low blower speed is requested, the PWM signal is reduced. When a higher blower speed is requested, the PWM signal is increased. The blower motor control processor interprets the PWM signal and varies the ground on the blower motor control circuit internally. An open circuit, short to ground, or short to battery on the blower motor speed control circuit will disrupt the PWM signal and cause the blower motor to not operate. In automatic operation, the HVAC control module will determine what blower speed is necessary in order to achieve or maintain a desired temperature. Toggling the blower button manually also activates the liquid crystal display (LCD) display for the blower speed selected.

Off Mode

When the vehicle is moving, air flowing over the vehicle increases the air pressure just ahead of the windshield. This forces air into the outside air inlet, into the HVAC module and out through the floor outlets. The HVAC control module attempts to match the inside air temperature and driver selected temperatures. Since the air conditioning (A/C) compressor is not running, the incoming air may be warmed but not cooled. Press the driver side air temperature switch to turn off the HVAC system. The ambient air temperature will show on the display.

Recirculation Mode

When the recirculation switch is pressed, the HVAC control module will apply a ground to one of the recirculation door control circuits in order to obtain the desired position. The recirculation actuator is a reverse polarity motor, each circuit provides both power and ground to the recirculation actuator. When the actuator is being held in a stationary position, both of the recirculation door control circuits have 12 volts applied to both sides of the actuator motor. This holds the actuator stationary. When a recirculate position is requested, one of the recirculation door control circuits will ground driving the recirculation actuator into the desired position. When an outside air position is requested, the other recirculation door control circuit will ground. This moves the recirculation actuator into an outside air position. This brings air from outside the vehicle instead of air from the inside.

The HVAC control module provides power and ground to the recirculation actuator. The HVAC control module receives power from the under hood electrical center through the ignition 3 voltage circuit. Ground is provided by the ground circuit.

The recirculation mode can be used in both automatic and manual operation. The only time recirculation is not available is when FRONT DEFROST and mix blend mode is selected. The RECIRC LED will flash to alert the driver that recirculation mode is not available. Pressing the recirculation switch, from the OFF position, will set the blower, mode and A/C compressor clutch into automatic mode.

When in automatic mode, recirculation will stay on until either the vehicle operator selects outside air, by pressing the RECIRCULATION switch, or the HVAC control module automatically moves the recirculation actuator. Automatic recirculation is only available when air temperatures are 21°C (70°F) or warmer. The recirculation actuator position will vary to obtain a cooler duct air temperature when cool air is selected. This will assist in cooling the vehicle quicker.

The HVAC control module will move the recirculation actuator to the outside air position at ignition off to bring fresh air to replace stale air that has accumulated in the HVAC module during shut down.

When requested the recirculation actuator will be able to move to the 100 percent recirculation position for a limited time, after that limited time the actuator will move to the 90 percent position. In the auto mode only, the recirculation actuator will move faster to the recirculation position when vehicle is at an idle compared to the normal speed of the actuator during normal operation.

If the recirculation actuator or related circuits has a failure the HVAC control module will attempt to drive the actuator to the outside air position regardless of mode selection. If there is a failure with one of the air temperature actuators the HVAC control module will allow the recirculation actuator to move to the outside air position.

Automatic Modes

The automatic HVAC system will warm up/cool down and maintain the interior temperature of the vehicle by controlling the A/C compressor clutch, blower motor, air temperature, mode and recirculation actuators to achieve the desired temperature. For fully automatic operation, both the blower and mode buttons must be in the AUTO position. Blower speeds will change automatically based on inputs to the HVAC control module . The HVAC control module will always come back to the last settings after an ignition cycle or, if equipped, to the last settings of the driver by pressing the UNLOCK button on the remote keyless entry fob and placing the ignition in RUN. Only RECIRCULATION will have to be reset after each ignition cycle.

Moisture tends to accumulate in the HVAC module assembly after the engine has been shut OFF. The HVAC control module will purge the HVAC module of stale air and moisture to prevent window fogging. The mode actuator will move to the floor mode and run the low speed blower for 10 seconds to purge out the air and moisture. The recirculation actuator will be in the outside air position. Purge mode can be bypassed if any manual modes are selected.

In cold temperatures, the automatic HVAC system will provide heat in the most efficient manner. On cold engine start-up, when temperatures are -1°C (30°F) or colder, low blower speeds will be selected and airflow will be directed on the windshield for 3 minutes. This is done to prevent windshield fogging. To warm the interior quickly, maximum heat mode is used where the blower is at maximum speed, floor mode, both air temperature actuators are in full hot position and outside air is being drawn in. The vehicle operator can select the extreme warm setting of 32°C (90°F), but the system will be out of automatic operation and not warm the vehicle any faster or regulate the blower speed. Once the desired temperature is reached, the blower motor, mode, recirculation and temperature will be adjusted automatically by the HVAC control module.

In warm temperatures, the automatic HVAC system will provide A/C in the most efficient manner. On vehicle start-up, the HVAC control module will monitor for conditions that indicate the possible presence of moisture in the HVAC module. To avoid blowing hot air and moisture out at the driver, the HVAC control module moves the mode door toward the floor and runs the low speed blower for a 3 seconds. This purge mode can be bypassed if the vehicle is started with the blower switch in maximum speed position. To cool the interior quickly, maximum cool mode is used where the blower is at maximum speed, both air temperature actuators are in full cold position and the recirculation actuator is drawing air from inside the vehicle. The vehicle operator can select the extreme cool setting of 16°C (60°F), but the system will be out of automatic operation and not cool the vehicle any faster or regulate the blower speed. Once the desired temperature is reached, the blower motor, mode, recirculation and temperature will be adjusted automatically by the HVAC control module.

When the mode switch is pressed, a ground is provided from the HVAC control module to the mode actuator through the mode door control circuits. When the mode actuator receives the signal, the mode actuator moves into the desired position.

The HVAC control module provides power and ground to the mode actuator. The HVAC control module receives power from the rear fuse block through the ignition 3 voltage circuit. Ground is provided by the ground circuit.

The mode actuator is a reverse polarity motor. Each circuit provides both power and ground to the mode actuator. When the mode actuator is being held in position, both of the mode door control circuits have 12 volts applied to both sides of the actuator motor. This holds the actuator stationary. When a mode is requested, one of the mode door control circuits will ground, driving the mode actuator into the desired mode.

Front Defrost Mode

The front defrost mode is the only setting that is not controlled by the automatic HVAC system. When defrost is selected, by the vehicle operator, the A/C compressor is activated and outside air is brought into the vehicle. The blower motor will be activated, regardless of coolant temperature and air will be directed toward the windshield, the side windows and some air flow to the floor. Recirculation mode is not available in front defrost. The recirculation LED will flash on their respective displays if any of those switches are pressed when in front defrost mode. This indicates that these modes are not available. The rear window defogger does not affect the HVAC system in any setting.

Mode Switch

Use the MODE switch in order to change the air delivery mode in the vehicle. Selection of the MODE switch when in AUTO mode will lock in the air flow mode that AUTO was controlling. The system will stay in that mode until the MODE or AUTO switch is pressed. Toggling the MODE button also activates the LCD display for the mode selected. If an airflow mode is currently displayed, pressing the MODE button selects the next air flow mode. The air flow direction will sequence through the following modes:

These are the only air flow modes available through the MODE button. When in AUTO mode, the HVAC control module will only operate in the following modes:

Dual Zone Control Switch

The passenger air temperature switch is provided to allow the passenger to set air discharge temperatures on the passenger side of the vehicle. Passenger temperatures can be set from 15-32°C (60-90°F). To activate the dual zone, the passenger air temperature switch to the desired offset. If the passenger air temperature switch has been turned on, it can be turned off by pressing the passenger switch. Greater sunload on one side of the vehicle may cause the discharge air temperatures to be different, even when the HVAC system is not operating in a dual zone mode.

The HVAC control module provides power and ground to the passenger air temperature actuator. The HVAC control module receives power from the under hood electrical center through the ignition 3 voltage circuit. Ground is provided by the ground circuit.

The passenger air temperature actuator is a reverse polarity motor. Each circuit provides both power and ground to the passenger air temperature actuator. When the passenger air temperature actuator is being held in position, both of the passenger air temperature door control circuits have 12 volts applied to both sides of the actuator motor. This holds the actuator stationary. When a temperature offset is requested, one of the passenger air temperature door control circuits will ground, driving the passenger air temperature actuator into the desired temperature offset.

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 a wake. Outside ambient temperature sensor, OAT- on automatic systems or intake air temperature (IAT) on manual systems, are utilized to determine the moding of the following features: Blower Mode (Bi-level, floor, Defrost, Recirc and rear Defrost. These features as determined by the OAT/IAT during activation sequence are maintained for the duration of engine run time. Class 2 supplies the ambient temperature. Calibratable temperatures are utilized to provide low, mid and high temperature ranges for feature selectable. Blower and mode have the range to select any valid feature positions. When the remote start active serial data is received ignition-off loop HVAC algorithms will act the same as if a run power mode received (i.e. re-calibration, After blow, ignition-off motor positioning etc.) off timer and ignition on timer have the functionality as in Run mode.

Remote Start De-activation

When the remote start is exited (class 2 power mode = run mode or remote start engine), all displays will revert to that based on actual settings on the vehicle. In the case of manual settings, displays will revert to actual state of operation of the features on the basis of their normal control algorithms.