Avalanche 2500 4WD V8-8.1L VIN G (2003)
Air Door Actuator / Motor: Description and Operation
HVAC System - Automatic
AIR DELIVERY
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.
Auxiliary Mode Actuator
The auxiliary 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 auxiliary 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.
Auxiliary Blower Motor Control Processor
The auxiliary blower motor control processor controls the speed of the blower motor by increasing or decreasing the voltage drop on the ground side
of the auxiliary blower motor. The auxiliary HVAC control module provides a low side pulse width modulated signal to the auxiliary blower motor
control processor over the auxiliary blower motor speed control circuit. As the requested blower speed increases, the auxiliary HVAC control module
increases the amount of time that the speed signal is modulated to ground. As the requested blower speed decreases, the auxiliary HVAC control
module decreases the amount of time that the signal is modulated to ground.
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 drive the actuator in one direction while 5-volts move 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.
AIR TEMPERATURE
Air Temperature Actuator
The air temperature actuators are 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.
Auxiliary Air Temperature Actuator
The auxiliary air temperature actuator is a 5-wire bi-directional electric motor that incorporates a feedback potentiometer. Ignition 3-voltage, low
