The air delivery controls are divided into 4 areas:
| • | HVAC Control Components |
| • | Air Speed |
| • | Air Distribution |
| • | 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 voltage circuit provides power that the control module uses for keep alive memory (KAM). If the battery positive voltage circuit loses power, all HVAC DTCs and settings will be erased from KAM. The control module supports the following features:
Feature | Availability |
|---|---|
Afterblow | Optional |
Purge | No |
Personalization | No |
Actuator Calibration | Yes |
Mode/Recirculation Actuator
The mode/recirculation actuator is a 2 wire bi-directional electric motor. Two 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 volts. In order to move the actuator, the HVAC control module grounds the appropriate control circuit for the commanded direction. The HVAC control module reverses the polarity of the control circuits to move the actuator in the opposite direction.
The HVAC control module determines the door position by counting motor pulses on one of the control circuits. These pulses are small voltage fluctuations that occur when the brush is shorted across 2 commutator contacts as the motor rotates. As the actuator shaft rotates, the HVAC control module monitors the voltage drop across an internal resistance to detect the pulses. The HVAC control module converts the pulses to counts with a range of 0-255 counts. The HVAC control module uses a range of 0-255 counts to index the actuator position.
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. |
| • | 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. |
| • | 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. |
| • | Recalibration will typically occur when the engine is OFF. The actuator noise heard during recalibration may be more noticeable than during normal operation. |
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, with the exception of afterblow.
Once a blower speed is selected, the blower speed remains constant, until a new speed is selected. When OnStar® System is activated the blower speed will be reduced.
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 following conditions must be met for afterblow to operate:
| • | The A/C compressor operated for more than 15 seconds. |
| • | The system voltage is at least 11 volts to start and 10 volts to continue to run. |
| • | The ignition has been in the OFF position for at least 20 minutes. |
Once the above conditions have been met, the blower will turn ON for 5 minutes and run at 30 percent blower speed.
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 switch is moved to heater 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 the blower is ON and the power mode is in Run. |
| • | The A/C compressor will follow user request if the blower is ON and the 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 heater through defrost. The recirculation LED will flash 3 times indicating recirculation is not available. The operator must activate the blower for Recirculation operation. The A/C compressor will engage while in the recirculation position. Every time the vehicle or HVAC system is turned off, the system will default to outside air unless the mode is in heater through defrost position.
Remote Start
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/awake. The OAT sensor on manual systems, is utilized to determine the moding of the following features: Blower Mode (Bi-level, Floor, Defrost, Recirc and Rear Defrost. These features are determined by the OAT during activation sequence and are maintained for the duration of engine run time. Calibratable temperatures are utilized to provide low, mid and high temperature ranges for the selectable feature. 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 was received, i.e. re-calibration, afterblow, ignition-OFF motor positioning etc. The OFF timer and the ignition ON timer have the functionality as in the Run mode.
Remote Start De-activation
When the remote start is exited, GMLAN power mode equals run mode or remote start engine. In the case of manual settings, the displays will revert to the actual state of operation of the features, on the basis of their normal control algorithms.
