The air delivery description and operation is divided into 5 areas:
• | HVAC Control Components |
• | Recirculation Operation |
HVAC Control Components
HVAC Control Module
The HVAC control module is a class 2 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 body control module (BCM), which
is the vehicle mode master, provides a device on signal. The control module supports
the following features:
Feature
| Availability
|
Afterblow
| No
|
Purge
| No
|
Personalization
| Yes
|
Actuator Calibration
| Yes
|
Mode Actuator
The mode 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 either 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 HVAC control module 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 module 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 module. Once the position signal and the commanded
value are the same, the module changes the control signal to 2.5 volts.
Blower Motor Control Processor
The blower motor control processor controls the speed of the blower motor by
increasing or decreasing the voltage drop on the ground side of the blower motor.
The HVAC control module provides a low side pulse width modulated signal to the blower
motor control processor over the blower motor speed control circuit. As the requested
blower speed increases, the HVAC control module increases the amount of time that
the speed signal is modulated to ground. As the requested blower speed decreases,
the HVAC control module decreases the amount of time that the signal is modulated
to ground.
Air Speed - Front Control
The blower control switch is integrated into the HVAC control module. The 2
rocker type switches provide the vehicle operator the ability to select several blower
speeds. The HVAC control module uses a bar graph type display to indicate the selected
blower speed. The HVAC control module provides a pulse width modulated (PWM) signal
to the blower motor through the blower motor speed control circuit. The blower motor
changes speed based on the received PWM signal from the HVAC control module. Power
and ground are provided to the blower motor through the battery positive voltage and
ground circuits. When the HVAC control module is operating in AUTO mode, the system
automatically controls the blower speed. Power and ground are provided to the HVAC
control module by the ignition 3 voltage and the ground circuits.
Air Distribution
The HVAC control module controls the distribution of air by the use of a mode
actuator. The modes that may be selected are:
The mode actuator is connected to the mode door by a cam type linkage system.
Depending on the position of the door, air is directed through the HVAC module and
distributed through various ducts leading to the outlets in the dash. If the HVAC
control module detects a fault with the mode door, the HVAC control module will try
to drive the actuator for a predetermined amount of time, to defrost, which is the
defaulted position for the mode door actuator. When the mode switch is placed in the
defrost or defog positions the A/C is commanded on and the recirculation door is moved
to the outside air position to help reduce window fogging. A/C is available in all
modes and recirculation is only available in the panel and bi-level modes.
Mode Actuator
The mode actuator is an electronic stepper motor with feedback potentiometers.
The HVAC control module sends signals to the mode door actuator through the mode
door control circuit. Zero volts drives the actuator in one direction while 5 volts
moves the actuator in the opposite direction. When the actuator receives 2.5 volts,
the actuator rotation stops. A 5-volt reference signal is sent out over the 5-volt
reference circuit to the mode actuator. When you select a desired mode setting, logic
determines the value of the mode actuator signals. The HVAC control module's software
uses this reference voltage in order to determine the position of the mode actuator
through the mode door position signal circuit. The motor moves the mode door to the
desired position.
Front Defrost
When defrost is selected, the A/C compressor is activated. The A/C compressor
clutch will engage when ambient temperatures are above 3°C (38°F). The blower
motor will be activated, regardless of the coolant temperature. The HVAC control module
will override the auxiliary HVAC control module so a high volume of air is delivered
to the front defrost vents. The rear window defogger does not affect the HVAC system.
Recirculation Operation
The HVAC control module controls the air intake through the recirculation actuator.
The recirculation switch closes the recirculation door in order to circulate the air
within the vehicle. The outside air switch opens the recirculation door in order to
route outside air into the vehicle. Regardless of the blower motor switch position,
recirculation is available only in the panel and bi-level mode switch positions. Including
the OFF position. The mode switch must be placed in either the panel or bi-level position
before the blower motor switch is placed in the OFF position. In order to reduce windshield
fogging, outside air is circulated when the mode switch is in the defrost or defog
positions. 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 3 times. If the HVAC control module detects a fault with the recirc door the
HVAC control module will try to drive the actuator for a predetermined amount of time,
to outside air, which is the defaulted position for the recirculation actuator.
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.
To place the HVAC system in Automatic mode, the following is required:
• | The Auto switch must be activated. |
• | The air temperature switch must be in any other position other than full
hot or full cold position. |
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:
• | Monitor the following sensors: |
- | Inside air temperature sensor |
- | Ambient Air Temperature Sensor |
- | Lower Left Air Temperature Sensor |
- | Lower Right Air Temperature Sensor |
- | Upper Left Air Temperature Sensor |
- | Upper Right Air Temperature Sensor |
• | Regulate blower motor speed |
• | Position the air temperature actuator |
• | Position the mode actuator |
• | Position the recirculation actuator |