The air delivery description and operation is divided into six areas:

HVAC Control Module

The HVAC control module is not 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:

Auxiliary HVAC Control Processor

The auxiliary HVAC control processor controls all outputs for the auxiliary HVAC system. It receives inputs from the front and rear auxiliary HVAC control assemblies. The processor positions the auxiliary air temperature actuator and auxiliary mode actuator based on these inputs. This processor does not have Class 2 communication available.

The auxiliary HVAC control processor receives power from the ignition 3 voltage circuit. Ground is provided by the ground circuit through rear auxiliary HVAC control assembly and a splice pack. The system receives 12 volt varied voltage input for auxiliary air temperature change request. Then the processor creates a 12 volt varied output for control of the auxiliary air temperature actuator. When the voltage signal is low a cool air request is made and the voltage signal is high a warm air request is made.

Front Auxiliary HVAC Control Assembly

The front auxiliary HVAC control assembly provides inputs to the auxiliary HVAC control processor. It is located in the overhead console so that front seat occupants can control auxiliary HVAC operation. This assembly provides blower, air delivery mode, air temperature settings and control of which control unit will operate the auxiliary HVAC system. When the REAR position is selected, inputs from this control assembly will not be processed by the auxiliary HVAC control processor. This system does not have Class 2 communication available.

The front auxiliary HVAC control assembly receives power from the ignition 3 voltage circuit. The front HVAC control assembly will apply a ground to the rear auxiliary enable control circuit when REAR is selected. When the air temperature knob is rotated a variable resistor internal to the assembly will vary a 12 volt input. The 12 volt varied voltage is supplied to the auxiliary HVAC control processor for an auxiliary air temperature actuator position change request. This is done on the auxiliary air temperature door position signal circuit . When the voltage signal is low a cool air request is made and the voltage signal is high a warm air request is made.

Rear Auxiliary HVAC Control Assembly

The rear auxiliary HVAC control assembly provides inputs to the auxiliary HVAC control processor. It is located in the rear headliner so that second row seat occupants can control auxiliary HVAC operation. This assembly provides blower, air delivery mode and air temperature settings. When the REAR position is selected, on the front HVAC control assembly, inputs from this control assembly will be processed by the auxiliary HVAC control processor. This system does not have Class 2 communication available.

The rear auxiliary HVAC control assembly receives power from the ignition 3 voltage circuit. The front HVAC control assembly will apply a ground to the rear auxiliary enable control circuit when REAR is selected. When the air temperature knob is rotated a variable resistor internal to the assembly will vary a 12 volt input. The 12 volt varied voltage is supplied to the auxiliary HVAC control processor for an auxiliary air temperature actuator position change request. This is done on the auxiliary air temperature door position signal circuit . When the voltage signal is low a cool air request is made and the voltage signal is high a warm air request is made.

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 3 wire bi-directional electric motor. Ignition 3 voltage, ground and control circuits enable the actuator to operate. The control circuit uses a 0-12 volt linear-ramped signal to command the actuator movement. The 0 and 12 volt control values represent the opposite limits of the actuator range of motion. The values in between 0 and 12 volts correspond to the positions between the limits.

When the auxiliary HVAC control processor sets a commanded, or targeted, value, the control signal is set to a value between 0-12 volts. The actuator shaft rotates until the commanded position is reached. The module will maintain the control value until a new commanded value is needed.

The blower motor forces outside air into the vehicle's interior. The vehicle operator determines the blower motor's speed when the driver places the blower switch in one of 5 blower speeds. The blower motor will always operate in any switch position other than OFF, as long as the ignition switch is in the RUN position. The blower motor and mode switches are located within the HVAC control module. The blower motor OFF input is connected in series with the HVAC control module by the off blower motor control circuit.

Depending upon the selected speed, power is provided to the blower motor from either the ignition 3 voltage or battery positive voltage circuits from the fuse block. The battery positive voltage circuit only provides power when the High blower switch position is selected. Power and ground are provided to the HVAC control module by the ignition 3 voltage and the ground circuits.

Low Blower Speed

When the Low 1 blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the low blower motor control circuit. Voltage is divided between 4 series resistors, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.

Medium Blower Speeds

When the Medium 1 blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the medium 1 blower motor control circuit. Voltage is divided between 3 series resistors, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.

When the Medium 2 blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the medium 2 blower motor control circuit. Voltage is divided between 2 series resistors, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.

When the Medium 3 blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the medium 3 blower motor control circuit. Voltage is divided between a series resistor, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.

High Blower Speed

When the High blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the high blower motor control circuit. The voltage energizes the blower relay, causing the blower motor to be connected directly to the battery positive voltage circuit. The blower motor and blower motor relay are grounded through the ground circuit.

There are two separate control assemblies for the auxiliary HVAC system. There is the front auxiliary HVAC control assembly and the rear auxiliary HVAC control assembly. Both control assemblies provide input to the auxiliary HVAC control processor. If the front auxiliary HVAC control assembly is in any other position than OFF or REAR, the auxiliary HVAC control processor will only use inputs from the front HVAC controls. If the front auxiliary HVAC control assembly is in the REAR position, then the system will only function with inputs from the rear auxiliary HVAC control assembly. If the front auxiliary HVAC control assembly is in the OFF position, then the auxiliary HVAC control processor does not respond to input from either control assembly. The auxiliary HVAC control processor can not request A/C compressor clutch engagement from the PCM. The rotary switches on the auxiliary HVAC control module and the front auxiliary HVAC control assembly provide the operator the ability to select several blower speeds.

Off Mode

When the OFF blower setting is selected on the front auxiliary HVAC control assembly, the switch creates an open circuit within the front auxiliary HVAC control assembly. This prevents any output being provided by either the front or rear auxiliary HVAC control assembly. If the OFF blower setting is selected on the rear auxiliary HVAC control assembly, the switch will create an open within the rear auxiliary HVAC control assembly. This prevents any output being provided to the auxiliary blower motor, as long as the front auxiliary HVAC control assembly is in the OFF position. The front auxiliary HVAC control assembly controls the rear auxiliary HVAC control assembly on the auxiliary blower motor switch control circuit.

Auxiliary Low Blower Speed

When the Low blower speed is selected at the front auxiliary HVAC control assembly, the front auxiliary HVAC control assembly applies a ground to the auxiliary low speed blower motor relay through the auxiliary blower motor low speed control circuit. When the relay closes its switch, voltage is provided by the battery positive voltage circuit. Voltage is divided between 2 series resistors in the auxiliary blower motor resistor assembly and the auxiliary blower motor to achieve the desired blower speed. The auxiliary blower motor is included in the series circuit by the auxiliary blower motor supply voltage and ground circuits. The auxiliary blower motor switch and auxiliary blower motor are grounded by the ground circuit.

When the Low blower speed is selected at the rear auxiliary HVAC control assembly, the rear auxiliary HVAC control assembly applies a ground to the auxiliary low speed blower motor relay through the auxiliary blower motor low speed control circuit, the auxiliary blower motor switch control circuit, the auxiliary HVAC control processor, then through the REAR CNTL switch position on the front auxiliary HVAC control assembly. When the auxiliary low speed blower motor relay closes its switch, voltage is provided by the battery positive voltage circuit. Voltage is divided between 2 series resistors in the auxiliary blower motor resistor assembly and the auxiliary blower motor to achieve the desired blower speed. The auxiliary blower motor is included in the series circuit by the auxiliary blower motor supply voltage and ground circuits. The auxiliary blower motor switch and auxiliary blower motor are grounded by the ground circuit.

Auxiliary Medium Blower Speed

When the Medium blower speed is selected at the front auxiliary HVAC control assembly, the front auxiliary HVAC control assembly applies a ground to the auxiliary medium speed blower motor relay through the auxiliary blower motor medium speed control circuit. When the relay closes its switch, voltage is provided by the battery positive voltage circuit. Voltage is divided between 1 series resistor in the auxiliary blower motor resistor assembly and the auxiliary blower motor to achieve the desired blower speed. The auxiliary blower motor is included in the series circuit by the auxiliary blower motor supply voltage and ground circuits. The auxiliary blower motor switch and auxiliary blower motor are grounded by the ground circuit.

When the Medium blower speed is selected at the rear auxiliary HVAC control assembly, the rear auxiliary HVAC control assembly applies a ground to the auxiliary medium speed blower motor relay through the auxiliary blower motor medium speed control circuit, the auxiliary blower motor switch control circuit, the auxiliary HVAC control processor, then through the REAR CNTL switch position on the front auxiliary HVAC control assembly. When the auxiliary medium speed blower motor relay closes its switch, voltage is provided by the battery positive voltage circuit. Voltage is divided between 1 series resistor in the auxiliary blower motor resistor assembly and the auxiliary blower motor to achieve the desired blower speed. The auxiliary blower motor is included in the series circuit by the auxiliary blower motor supply voltage and ground circuits. The auxiliary blower motor switch and auxiliary blower motor are grounded by the ground circuit.

Auxiliary High Blower Speed

When the High blower speed is selected at the front auxiliary HVAC control assembly, the front auxiliary HVAC control assembly applies a ground to the auxiliary high speed blower motor relay through the auxiliary blower motor high speed control circuit. When the relay closes its switch, voltage is provided by the battery positive voltage circuit. Voltage is sent directly to the auxiliary blower motor by the auxiliary blower motor supply voltage circuit. The auxiliary blower motor switch and auxiliary blower motor are grounded by the ground circuit.

When the High blower speed is selected at the rear auxiliary HVAC control assembly, the rear auxiliary HVAC control assembly applies a ground to the auxiliary high speed blower motor relay through the auxiliary blower motor high speed control circuit, the auxiliary blower motor switch control circuit, the auxiliary HVAC control processor, then through the REAR CNTL switch position on the front auxiliary HVAC control assembly. When the auxiliary high speed blower motor relay closes its switch, voltage is provided by the battery positive voltage circuit. Voltage is sent directly to the auxiliary blower motor by the auxiliary blower motor supply voltage circuit. The auxiliary blower motor switch and auxiliary blower motor are grounded by the ground circuit.

The HVAC control module controls the distribution of air by the use of a defrost actuator and 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.

The auxiliary HVAC system provides ventilation for the rear seat occupants. The rear seat occupants will exercise control of the auxiliary air delivery modes, air speed and the air temperature setting. The front auxiliary HVAC control assembly will have the ability to override the rear auxiliary HVAC control module by placing it in any position other than REAR

The auxiliary mode switch in the front auxiliary HVAC control assembly allows the driver to direct the air flow in the rear of the vehicle between the floor, headliner, or a blend between the two options. Power is provided to both the front auxiliary HVAC control assembly and the auxiliary mode actuator from the IP fuse block on the ignition 3 voltage circuit.

Voltage delivered to the front auxiliary HVAC control assembly on the ignition 3 voltage circuit is sent to a variable resistor. Based on the placement of the mode switch, a varied voltage is sent to the auxiliary mode actuator on the auxiliary mode door control circuit, and auxiliary HVAC control processor. The auxiliary mode actuator moves the mode door to the desired output. Ground for the auxiliary mode actuator, auxiliary HVAC control processor and front auxiliary HVAC control assembly are provided by the ground circuit.

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.