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 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 control module supports the following features:
Feature | Availability |
|---|---|
Afterblow | Optional |
Purge | No |
Personalization | No |
Actuator Calibration | Yes |
Mode/Recirculation Actuator
The Buehler 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 co-ordinate 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 to 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 three 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 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.
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. |
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 the bi-level 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 blower is on and power mode is in run. |
| • | The A/C compressor will follow user request if blower is on and 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 bi-level through defrost. The operator must activate the blower for Recirculation operation.
