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 non-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 to the control module. The ignition 3 voltage circuit provides a device on signal to the HVAC control module. The control module supports the following features:
Feature | Availability |
|---|---|
Afterblow | No |
Purge | No |
Personalization | No |
Actuator Calibration | Yes |
Upon initial ignition ON after a battery disconnect the HVAC control module will calibrate the air temperature and mode actuators. The next ignition cycle the HVAC control module takes the follow actions:
| • | The HVAC control module will first perform required memory diagnostics. If there is fault, then A/C request will be disabled and the recirculation door position will be defaulted to outside air position |
| • | Restore the A/C state from memory |
| • | Restore the recirculation actuator position from memory |
| • | Set the rear defrost output to OFF |
| • | Set the blower motor speed to the actual blower motor switch position |
| • | Set the mode door position to the actual mode switch position |
| • | Set the air temperature door position to the actual air temperature switch position |
Diagnostic trouble codes (DTC) are manually retrieved and cleared through the HVAC control module. Refer to Diagnostic Trouble Code (DTC) Displaying or Diagnostic Trouble Code (DTC) Clearing .
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.
When the HVAC control module sets a desired position the mode door 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 mode door control signal to 2.5 volts.
Recirculation Actuator
The 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 10 volt value to coordinate the actuator movement. The HVAC control module reverses the polarity of the control circuits to move the actuator in the opposite direction.
Air Speed
The HVAC control module applies a ground to the blower motor control circuit that corresponds to the selected blower speed. For only the medium 2 speed, the blower motor medium 3 control circuit is PWM controlled at 70 percent duty cycle. The resistors and the blower motor are in a series circuit. The following list represents the number of resistors in series with the blower motor for each speed request:
| • | Low speed 3 resistors |
| • | Medium 1 speed 2 resistors |
| • | Medium 2 speed 1 resistor and 70% Duty Cycle PWM |
| • | Medium 3 speed 1 resistor |
When the operator requests High speed, the HVAC control assembly applies ground to the blower motor high control circuit.
When the blower motor switch is placed to the OFF position the recirculation actuator is set to the recirculation position and the A/C request will be disabled. The air temperature actuator and mode positions are set to the actual switch position and are adjustable when the blower is OFF.
Air Delivery
The HVAC control module controls the mode actuator in order to distribute airflow to a desired outlet. When the mode switch is moved to the Defog, Defrost, or Maximum Defrost positions, the A/C compressor clutch engages and the recirculation actuator will be moved to the outside air position. The maximum defrost position also turns on the rear window defogger, sets the air temperature door position to full hot position and set the blower motor speed to High. Regardless of the mode setting, a small amount of air will be diverted to the defrost ducts to reduce windshield fogging. On startup, the HVAC control module will place the mode door to the actual mode switch position.
When the mode switched is placed from one of the three defrost positions to the Floor, Bi-level or the Vent position, the state of the A/C request will be restored to the previous setting.
Recirculation Operation
The HVAC control module controls the air intake through the recirculation actuator. Recirculation is only available when the HVAC control module is in Vent and Bi-level positions. When the blower motor switch is place in the OFF position the recirculation actuator will be commanded to the outside air position. The recirculation LED is illuminated when the recirculation actuator is in the recirculation position. Placing the recirculation switch to the ON position automatically creates an A/C request.
If the recirculation door is in the recirculation position in the panel or bi-level mode, then the mode door is placed to another mode position. The recirculation door will not be put back into recirculation position when placed back into panel or bi-level position. It must be manually selected again to obtain the recirculation position. If recirculation is selected in any other mode than panel or bi-level, then the indicator will flash four times to indicate that the position can not be obtained. The recirculation switch in inoperative if the blower motor switch is off.
