The air delivery description and operation is divided into 5 areas:

HVAC Control Module

The HVAC control module is a device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The control module sends switch input data to the instrument panel module (IPM), and receives display data from the IPM through signal and clock circuits. The ignition 3 voltage circuit provides a device on signal. The control module does not retain any HVAC DTCs or settings.

Instrument Panel Integration Module

A function of the IPM operation is to process HVAC system inputs and outputs. Also, the IPM acts as the HVAC control module's class 2 interface. The battery positive voltage circuit provides power that the IPM 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 ignition 3 voltage circuit provides a device on signal. The IPM supports the following features:

Mode/Recirculation Actuator

The flatpack 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 circuits enable the actuator to operate. The control circuit uses a 0, 2.5 or 5-volt signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 volts. A 0 or 5-volt control signal commands the actuator movement in opposite directions. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door position signal between 0-5 volts.

The IPM 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 IPM sets a commanded, or targeted, value, the control signal is changed to either 0 or 5 volts depending upon the direction that the actuator needs to rotate to reach the commanded value. As the actuator shaft rotates the changing, position signal is sent to the IPM. Once the position signal and the commanded value are the same, the IPM changes the control signal to 2.5 volts.

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 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.

The blower motor forces air to circulate within the vehicle's interior. The vehicle operator determines the blower motor's speed by placing the blower motor switch in a desired speed position or by selecting automatic operation. 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. 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.

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 underhood fuse block through the battery positive voltage circuit. Ground is provided by the blower motor control processor and ground circuits.

When any blower speed is selected, whether manually or automatically, the IPM receives an input from the HVAC control module. The IPM and HVAC control module communicate back and forth over the HVAC control module signal and the HVAC control module clock signal circuits. Once received by the IPM, a 5 volt pulse width modulated (PWM) signal is sent to the blower motor control processor on the blower motor speed control circuit. When a low blower speed is requested by the vehicle operator, the PWM signal is reduced. When a higher blower speed is requested, the PWM signal is increased. A 12 volt signal is then sent to the blower motor from the blower motor control processor on the blower motor supply voltage circuit. 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 IPM 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:

As the requested blower speed decreases, the following conditions occur:

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:

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

1. The blower will run for 20 seconds.
2. The blower will be off for 10 minutes.
3. The blower will run for 20 seconds.

Purge Operation

If the ambient air temperature is less than 2°C (35°F) and the coolant temperature is less than 10°C (50°F), then a 75-second purge will occur. The purge will begin as soon as the coolant temperature reaches 4°C (40°F). The mode door will move to the defrost position and the blower motor will be near half speed.

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. Regardless of the mode setting, a small amount of air will be diverted to the defrost ducts to reduce windshield fogging. When VENT is pressed, the following will occur:

After a malfunction occurs to the mode actuator it is driven to the Defrost position on startup, the HVAC control module will place the mode door in the last selected position.

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 ten minutes. The operator must activate the blower for Recirculation operation. The A/C high-pressure recirculation switch can cause the HVAC system to recirculate air. 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 three times. When the high side pressure reaches 2206-2620 kPa (320-380 psi), the PCM will place the HVAC system in recirculation mode. The high side pressure is lowered when the inside air cools the refrigerant within the A/C evaporator. When the high-side pressure reaches 1447-1861 kPa (210-270 psi), the PCM will place the HVAC system out of recirculation mode.

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 Automatic mode, the following is required:

Once the desired temperature is reached, the blower motor, mode, recirculation and temperature actuators will automatically be adjusted to maintain the temperature selected. The HVAC control module performs the following functions to maintain the desired air temperature: