Air Delivery Description and Operation CJ3

The air delivery controls are divided into two primary areas. The first, air speed, is dependent upon blower motor speed. The second, air distribution, is related to various single or multiple air outlets.

The blower motor forces ambient 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 the following positions:

The blower motor will operate in any switch position other than OFF, as long as the ignition switch is in the RUN position. When the ignition switch is ON, power from the fuse block is delivered to the blower motor switch through the ignition-3 voltage circuit. The blower motor and mode switches are located within the HVAC control module.

Power is provided to the blower motor from the fuse block. Depending upon selected blower speeds, voltage is either supplied directly to the blower motor or voltage is varied by a series of in-line resistors. Power and ground are provided to the HVAC control module by the ignition-3 voltage and ground circuit.

Low Blower Speed

When the Low 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 among 4 series resistors in the blower motor resistor assembly, the blower motor relay and the blower motor to achieve the desired blower speed. The blower motor is included in the series circuit by the blower motor supply voltage and ground circuits. The ground circuit provides a ground path for the blower motor.

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 among 3 series resistors in the blower motor resistor assembly, the blower motor relay and the blower motor to achieve the desired blower speed. The blower motor is included in the series circuit by the blower motor supply voltage and ground circuits. The ground circuit provides a ground path for the blower motor.

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 in the blower motor resistor assembly, the blower motor relay and the blower motor to achieve the desired blower speed. The blower motor is included in the series circuit by the blower motor supply voltage and ground circuits. The ground circuit provides a ground path for the blower motor.

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 in the blower motor resistor assembly, the blower motor relay and the blower motor to achieve the desired blower speed. The blower motor is included in the series circuit by the blower motor supply voltage and ground circuits. The ground circuit provides a ground path for the blower motor.

High Blower Speed

When the High blower speed is selected, the HVAC control module applies voltage to the blower motor relay through the high blower motor control circuit. When the load side of the relay is energized, the blower motor is connected directly to battery voltage through battery positive voltage circuit. The ground circuit provides a ground path for the blower motor.

Off Mode

When the Off position is selected, the HVAC control module applies voltage to the blower switch off input within the HVAC control module through the off blower motor control circuit. Fresh air will still be brought in from the outside.

Recirculation Mode

Recirculation is only available in MAX. When MAX mode is selected, vacuum is applied to the recirculation actuator. The force of the vacuum overcomes the spring pressure of the spring inside the actuator. This moves the actuator, which is linked to the recirculation door, into recirculation mode. This brings air from inside the vehicle instead of fresh air from the outside.

Mode Switch

Use the MODE switch in order to change the air delivery mode in the vehicle. The air flow direction will sequence through the following modes:

Vent Mode

When the driver selects the VENT mode, air is delivered through the instrument panel outlets and a small amount is delivered to the floor. Vacuum is applied to the mode actuator through the Brown vacuum line, and to the defrost actuator through the Red vacuum line. The mode actuator will retract, opening the Vent Door. The defroster actuator will retract, closing the Defroster Door and open the Heater Door through mechanical linkage.

Bi-Level Mode

When the driver selects the BI-LEVEL mode, cool air is delivered through the instrument panel outlets while warm air is delivered through the floor outlets. Vacuum is applied to the mode actuator through the Brown and the Blue vacuum lines, and to the defrost actuator through the Red vacuum line. Applying vacuum to both sides of the mode actuator will hold the Vent Door stationary in the half open position. The defroster actuator will retract, closing the Defroster Door and open the Heater Door through mechanical linkage.

Floor Mode

When the driver selects the FLOOR mode, air is delivered through the floor outlets with some toward the windshield and side vents. Vacuum is applied to the mode actuator through the Blue vacuum line, and to the defrost actuator through the Red vacuum line. The mode actuator will retract, closing the Vent Door. The defroster actuator will retract, closing the Defroster Door and open the Heater Door through mechanical linkage.

Mix-Blend Mode

When the driver selects the MIX-BLEND mode, air delivery is divided between the floor and windshield outlets. Vacuum is applied to the mode actuator through the Blue vacuum line, and to the defrost actuator through the Red and the Yellow vacuum lines. The mode actuator will retract, closing the Vent Door. Applying vacuum to both sides of the defroster actuator will hold the Defroster Door stationary in the half open position. The Heater Door will also be held stationary in the half open position through mechanical linkage.

Front Defrost Mode

If the HVAC system is in front defrost mode when you turn the vehicle off, the HVAC system will restart in front defrost unless the engine is off longer than 40 minutes. If the engine is off longer than 40 minutes, the system will restart in the previous operating mode set prior to using front defrost, with outside air being drawn into the vehicle.

When FRONT DEFROST is selected, the A/C compressor is activated and outside air is brought into the vehicle. Air will be directed toward the windshield with a small amount of air toward the side window outlets. Vacuum is applied to the mode actuator through the Blue vacuum line and to the defrost actuator through the Yellow vacuum line. The mode actuator will retract, closing the Vent Door. The defroster actuator will retract, opening the Defroster Door and close the Heater Door through mechanical linkage. Recirculation mode is not available in front defrost. The rear window defogger does not affect the HVAC system at all.

Outside Air Mode

When the OUTSIDE AIR switch is toggled, outside air is brought into the vehicle. This mode has no effect on the system when FRONT DEFROST mode is selected. OUTSIDE AIR and RECIRCULATION are separate modes and are not available together.

Recirculation Mode

When the recirculation switch is pressed, a solenoid inside the HVAC control module connects the recirculation vacuum actuator to the vacuum source. Power is provided to the recirculation switch by the ignition 3 voltage circuit. Ground is provided by the ground circuit and splice pack. The recirculation actuator retracts, closing the recirculation door. This brings air from inside the vehicle instead of fresh air from the outside.

Recirculation is available in all modes except FRONT DEFROST and MIX-BLEND. The recirculation mode will stay on and the LED will illuminate until either outside air or a non-recirculation mode is selected. The HVAC control module will stay in recirculation mode for 30 minutes after the ignition switch has been turned off. Recirculation can be selected with the blower motor in either the ON or OFF position.

Air Delivery Description and Operation CJ4

The air delivery controls are divided into two primary areas. The first, air speed, is dependent upon blower motor speed. The second, air distribution, is related to various single or multiple air outlets.

The blower motor forces ambient air into the vehicle's interior. The vehicle operator determines the blower motor's speed by toggling the blower motor switch. The blower motor will always operate at some speed as long as the HVAC control module is in any position other than OFF, and the ignition switch is in the RUN position.

Power is provided to the blower motor from the blower motor control processor through the blower motor supply voltage circuit. The blower motor control processor receives power from the fuse block through the battery positive voltage circuit. Ground is provided by the blower motor control processor and ground circuit.

The HVAC control module receives power from the fuse block on the ignition-3 voltage circuit along with the battery positive voltage circuit. The module is grounded by the ground circuit. The HVAC control module communicates directly to the powertrain control module (PCM) on the HVAC class 2 serial data circuit, through a splice pack, and through the ECM/PCM/VCM class 2 serial data circuit.

When any blower speed is selected, the blower motor control processor will control blower motor speeds based on voltage signals from the HVAC control module. A 5-volt signal is sent from the blower motor control processor to the HVAC control module on the blower motor speed control circuit. When the driver selects a blower speed, the HVAC control module will provide a varying ground. The remaining voltage at the blower motor control processor is used to provide a blower motor speed signal. A 12 volt signal is sent to the blower motor from the blower motor control processor on the blower motor supply voltage circuit. The blower motor control processor varies the ground on the blower motor control circuit internally with a separate PWM signal. An open circuit, short to ground or short to battery on the blower motor speed control circuit will disrupt the PWM signal and cause the blower motor to not operate. The blower motor flange ground circuit is used to limit radio frequency interference and does not affect blower operation.

When the HVAC control module is in the OFF position, pressing the blower motor switch will turn on the HVAC control module to the previous settings. In the event that both fan buttons are activated simultaneously in opposite directions, the blower speed shall not change until one switch is released, and the switch remaining activated will change the blower speed. If both switches are activated in the same direction simultaneously, then fan speed may change as with a single switch actuation.

On Mode

Pressing the ON switch will turn on the HVAC system to the most recent mode and fan settings.

Off Mode

Press the OFF switch to turn off the HVAC system. When the vehicle is moving, air flowing over the vehicle increases the air pressure just ahead of the windshield. This forces air into the HVAC air inlet and out through any desired mode setting. The temperature switch can be adjusted to warm the incoming air.

Recirculation Mode

When the recirculation mode is requested, a solenoid inside the vacuum control assembly connects the recirculation actuator to the vacuum source. Power is provided to the recirculation solenoid by the ignition-3 voltage circuit. Ground is provided by the recirculation mode valve solenoid control circuit and HVAC control module. When the solenoid is grounded, vacuum is supplied to the recirculation actuator. The recirculation actuator retracts, closing the recirculation door. This draws air from inside the vehicle instead of fresh air from the outside.

The only time recirculation not is available is when MIX-BLEND and FRONT DEFROST are selected. If the recirculation switch is pressed and recirculation is not available, the RECIRC LED will flash 3 times to alert the driver that recirculation mode is not available.

With the auxiliary HVAC system, the rear passengers can maintain separate temperature and mode settings. Pressing any switch on the auxiliary HVAC control module when the front HVAC control module is OFF will turn on the system.

The blower motor forces ambient air into the vehicle's interior. The rear passenger determines the blower motor's speed by toggling the auxiliary blower motor switch. The blower motor will always operate at some speed as long as the auxiliary HVAC control module is in any position other than OFF, and the ignition switch is in the RUN position.

Power is provided to the auxiliary HVAC control module on the ignition-3 voltage circuit. Ground is provided by the ground circuit. Power is provided to the blower motor from the blower motor control processor through the blower motor supply voltage circuit. The blower motor control processor receives power from the fuse block through the battery positive voltage circuit. Ground is provided by the blower motor control processor and ground circuit.

The HVAC control module receives power from the fuse block on the ignition-3 voltage circuit along with the battery positive voltage circuit. The module is grounded by the ground circuit. The HVAC control module communicates directly to the powertrain control module (PCM) on the HVAC class 2 serial data circuit, through a splice pack, and through the ECM/PCM/VCM class 2 serial data circuit.

When the rear passenger toggles the blower motor switch, internal resistors within the auxiliary HVAC control module varies the voltage from the internal ignition-3 voltage circuit. That varied voltage is sent to the HVAC control module through the auxiliary blower motor speed control circuit.

Once the HVAC control module receives the signal from the auxiliary HVAC control module, the blower motor control processor will control blower motor speeds based on voltage signals from the HVAC control module. A 5-volt signal is sent from the blower motor control processor to the HVAC control module on the blower motor speed control circuit. When the rear passenger selects a blower speed, the HVAC control module will provide a varying ground. The remaining voltage at the blower motor control processor is used to provide a blower motor speed signal. A 12-volt signal is sent to the blower motor from the blower motor control processor on the blower motor supply voltage circuit. The blower motor control processor varies the ground on the blower motor control circuit internally with a separate PWM signal. An open circuit, short to ground or short to battery on the blower motor speed control circuit will disrupt the PWM signal and cause the blower motor to not operate. The blower motor flange ground circuit is used to limit radio frequency interference and does not affect blower operation.

In the event that both fan buttons are activated simultaneously in opposite directions, the blower speed shall not change until one switch is released, and the switch remaining activated will change the blower speed. If both switches are activated in the same direction simultaneously, then fan speed may change as with a single switch actuation.

Mode Switch

Use the MODE switch in order to change the air delivery mode in the vehicle. The air flow direction will sequence through the following modes:

Vent Mode

When the driver selects the VENT mode, air is delivered through the instrument panel outlets and a small amount is delivered to the floor. Vacuum is applied to the mode actuator through the Brown vacuum line, and to the defrost actuator through the Red vacuum line. The mode actuator will retract, opening the Vent Door. The defroster actuator will retract, closing the Defroster Door and open the Heater Door through mechanical linkage.

Bi-Level Mode

When the driver selects the BI-LEVEL mode, cool air is delivered through the instrument panel outlets while warm air is delivered through the floor outlets. Vacuum is applied to the mode actuator through the Brown and the Blue vacuum lines, and to the defrost actuator through the Red vacuum line. Applying vacuum to both sides of the mode actuator will hold the Vent Door stationary in the half open position. The defroster actuator will retract, closing the Defroster Door and open the Heater Door through mechanical linkage.

Floor Mode

When the driver selects the FLOOR mode, air is delivered through the floor outlets with some toward the windshield and side vents. Vacuum is applied to the mode actuator through the Blue vacuum line, and to the defrost actuator through the Red vacuum line. The mode actuator will retract, closing the Vent Door. The defroster actuator will retract, closing the Defroster Door and open the Heater Door through mechanical linkage.

Mix-Blend Mode

When the driver selects the MIX-BLEND mode, air delivery is divided between the floor and windshield outlets. Vacuum is applied to the mode actuator through the Blue vacuum line, and to the defrost actuator through the Red and the Yellow vacuum lines. The mode actuator will retract, closing the Vent Door. Applying vacuum to both sides of the defroster actuator will hold the Defroster Door stationary in the half open position. The Heater Door will also be held stationary in the half open position through mechanical linkage.

Front Defrost Mode

If the HVAC system is in front defrost mode when you turn the vehicle off, the HVAC system will restart in front defrost unless the engine is off longer than 40 minutes. If the engine is off longer than 40 minutes, the system will restart in the previous operating mode set prior to using front defrost, with outside air being drawn into the vehicle.

When FRONT DEFROST is selected, the A/C compressor is activated and outside air is brought into the vehicle. Air will be directed toward the windshield with a small amount of air toward the side window outlets. Vacuum is applied to the mode actuator through the Blue vacuum line and to the defrost actuator through the Yellow vacuum line. The mode actuator will retract, closing the Vent Door. The defroster actuator will retract, opening the Defroster Door and close the Heater Door through mechanical linkage. Recirculation mode is not available in front defrost. The rear window defogger does not affect the HVAC system at all.

Outside Air Mode

When the OUTSIDE AIR switch is toggled, outside air is brought into the vehicle. This mode has no effect on the system when FRONT DEFROST mode is selected. OUTSIDE AIR and RECIRCULATION are separate modes and are not available together.

Recirculation Mode

When the recirculation switch is pressed, a solenoid inside the HVAC control module connects the recirculation vacuum actuator to the vacuum source. Power is provided to the recirculation switch by the ignition 3 voltage circuit. Ground is provided by the ground circuit and splice pack. The recirculation actuator retracts, closing the recirculation door. This brings air from inside the vehicle instead of fresh air from the outside.

Recirculation is available in all modes except FRONT DEFROST and MIX-BLEND. The recirculation mode will stay on and the LED will illuminate until either outside air or a non-recirculation mode is selected. The HVAC control module will stay in recirculation mode for 30 minutes after the ignition switch has been turned off. Recirculation can be selected with the blower motor in either the ON or OFF position.

With the auxiliary HVAC system, the rear passengers can maintain separate temperature and mode settings. Pressing any switch on the auxiliary HVAC control module when the front HVAC control module is OFF will turn on the system.

When the auxiliary mode switch is toggled, a signal is sent from the auxiliary HVAC control module to the auxiliary mode actuator. Power is provided to both the auxiliary mode actuator and auxiliary HVAC control module on the ignition-3 voltage circuit. Ground is provided by the ground circuit.

When the rear passenger slides the mode switch, an internal variable resistor within the auxiliary HVAC control module varies the voltage from the internal ignition-3 voltage circuit. That varied voltage provides a signal to the auxiliary mode actuator on the auxiliary mode door control circuit to move the auxiliary mode actuator to one of the following positions:

Recirculation Mode

When the rear passenger presses the recirculation switch, internal resistors within the auxiliary HVAC control module varies the voltage from the internal ignition-3 voltage circuit. That varied voltage is sent to the HVAC control module through the recirculation/A/C request signal circuit. Once the signal is received by the HVAC control module, a voltage signal is sent back to the auxiliary HVAC control module on the auxiliary recirculation indicator signal circuit to illuminate the recirculation switch LED. If the HVAC control module is in a mode that does not allow recirculation, and the auxiliary recirculation switch is pressed, the auxiliary recirculation switch will flash to indicate that recirculation is not available.