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 air temperature and distribution settings. The battery positive and ignition 1 voltage circuits provide power to the control module. The control module supports the following features:
Feature | Availability |
|---|---|
After Blow | Yes |
Purge | No |
Personalization | No |
Actuator Calibration | Yes |
Mode Actuators - Defrost, Panel and Floor
The mode actuators are 5-wire bi-directional electric motors that incorporate a feedback potentiometer. Low reference, 5-volt reference, position signal, and 2 control circuits enable the actuators 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 potentiometer's adjustable contact changes the door position signal between 0-5 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 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 or low reference 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 microbial growth that can create undesireable odors. The vehicle does not come with the afterblow feature enabled. If the afterblow feature is required due to an odor concern, it must be turned on by the scan tool. Certain items need to have happened for afterblow to operate:
| • | The A/C compressor operated on the latest key cycle. |
| • | The system voltage is at least 12 volts 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 roughly 2 minutes. |
| • | The recirculation door moves to the outside air position. |
| • | The mode valve moves to the floor position. |
Air Delivery
The defrost, panel and floor actuators control air delivery. The HVAC control module controls these actuators in order to distribute airflow to a desired outlet. When the vehicle operator selects the defrost, mix-blend or floor positions, the A/C compressor clutch engages and the recirculation actuator will be moved to the outside air position. The flow of air during the various modes of operation is as follows:
| • | Panel--Outside Air and Recirculation inlet air setting, full air from Instrument Panel (I/P) outlets |
| • | Bi-Level--I/P and front and rear floor outlets |
| • | Floor--Small amount of air to the right and left side window outlets and a larger amount of air to the Front and Rear floor outlets |
| • | Mix-Blend--Floor and defroster outlets with a slight bleed to the I/P outlets |
| • | Defrost--Defrost outlets with a small amount of air to the right and left side window outlets and to the Driver Side floor outlet and a very small amount to the Rear floor outlet |
Recirculation Operation
The recirculation 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 actuators 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 potentiometer's adjustable contact changes the door position signal between 0-5 volts.
In some mode positions recirc function is not allowed. The following table shows the recirc and led functions:
Mode Position | Recirc Actuator Positioning | Indicator Light On Recirc Button |
|---|---|---|
Floor | Forced to outside air position. Recirc is not allowed in this mode. | When the recirc button is pressed the led will flash three times then turn off to indicate recirc function is not available in this mode. |
Defog | Forced to outside air position. Recirc is not allowed in this mode. | When the recirc button is pressed the led will flash three times then turn off to indicate recirc function is not available in this mode. |
Defrost | Forced to outside air position. Recirc is not allowed in this mode. | When the recirc button is pressed the led will flash three times then turn off to indicate recirc function is not available in this mode. |
Bi-Level | Recirc and outside air are allowed | When the recirc button is pressed the led will turn on and stay on to indicate recirc function is available and selected in this mode. |
Vent | Recirc and outside air are allowed | When the recirc button is pressed the led will turn on and stay on to indicate recirc function is available and selected in this mode. |
