Air Delivery Part 2

Body Ventilation Outlets
To allow the HVAC system to operate efficiently air must be allowed to enter and leave the vehicle even when the cabin is sealed, i.e. all movable windows are fully up. This is achieved by the installation body mounted ventilation outlets. Each outlet consists of a fluted plastic housing containing 2 flexible rubber seals. When positive cabin air pressure acts upon the seals, they will deflect outward to allow air to exit the vehicle. Air may only exit and not enter the vehicle via the body ventilation outlets. The ventilation outlet housing is retained to the body panel by 4 locking tabs located at each corner. Although not a regular maintenance item, the body outlets can be removed to clear away any dust or foreign matter that may impede them from operating efficiently. This is important for reasons of dust exclusion (outlets not sealing) or over pressurization of the cabin (outlets obstructed) causing poor HVAC system performance. The body ventilation outlets fulfil an additional function in allowing the doors or rear compartment lid to be closed without exerting undue air pressure upon the windows and dust seals of the vehicle. The body ventilation outlets are installed behind the rear bumper bar fascia. Two on the left side and one on the right side. Air moves from the cabin to the rear compartment via air grilles in the rear parcel tray and then to the outlets.

Vacuum Actuators
All ventilation doors on the HVAC unit, excluding the air mix doors, are opened and closed by vacuum actuators. These may be single stage or 2 stage type actuators. All actuators, excluding the panel actuator, have a composite metal and plastic housing with metal actuating rods. The panel actuator is the only 2 stage actuator and has an all metal housing and metal actuating rod.

Single Stage Vacuum Actuator - Operation
Each single stage actuator consists of a vacuum housing containing a spring, rubber diaphragm, and an actuating rod. When vacuum is applied to actuator the rubber diaphragm is pulled back, compressing the spring and retracting the actuating rod which is connected via one or more levers to an air distribution door. When vacuum is removed, the spring pushes the diaphragm and actuating rod back to its original position.

Two Stage Vacuum Actuator - Operation
The HVAC unit has doors that are required to open half way while another door closes fully. With normal single stage vacuum actuators this would require a complicated linkage set-up and additional actuators. To overcome this situation 2-stage actuators are used. Through their design they can move the actuating rod fully (2nd stage), half way (1st stage) and fully extended (no vacuum). This enables some doors housed within the HVAC unit to be only half open when a blend mode is selected, and other doors to be closed at the same time via another actuator. When vacuum is directed to the 1st stage vacuum port only the 1st stage rubber diaphragm is pulled (towards the rear of the housing), moving the actuator rod only half way. Once the 2nd and 1st stage ports have vacuum applied, both diaphragms are pulled towards the rear of the housing moving the actuator rod fully inwards to the 2nd stage. The extent of actuator rod travel in either 1st or 2nd stage is governed by compressing 2 springs on each vacuum diaphragm. Both these springs are of differing tensions.

Vacuum Tank
The vacuum tank is located on the left side of the HVAC case. This tank is used to maintain a vacuum to the vacuum actuators, which operate the different vent positions, during driving situations where the vacuum source is low such as full engine throttle. A one way check valve is located in the vacuum source line from the inlet manifold. Two vacuum lines are attached to the vacuum tank. The vacuum line located towards the front of the vehicle is the vacuum supply line from the engine inlet manifold. The vacuum line located towards the rear of the vehicle is the vacuum feed to the to the mode switch vacuum valve and the water valve vacuum switch mounted to the rear of the HVAC controller.

Vacuum Circuit
The vacuum generated within the engine inlet manifold is used to operate the HVAC vacuum actuators and the water valve. A vacuum tank located on the left side of the HVAC case is used to store vacuum for times when engine vacuum is low such as at full engine throttle. A check valve is fitted on the vacuum supply line between the inlet manifold and the vacuum tank to ensure that vacuum is maintained within the system at all times. The black plastic vacuum supply line on the HVAC unit supplies vacuum to the vacuum tank. The check valve is used to join the supply line to the hose connected to the inlet manifold. Vacuum from the vacuum tank is then directed through a white colored supply hose to the mode switch for HVAC door operation and from the tee to the water valve vacuum switch for water valve operation. From the water valve vacuum switch, vacuum moves into a orange plastic tube and then connects to the black hose inside the cabin at the instrument panel which in turn is connected to the vacuum operated heater water valve. When vacuum is applied to the water valve, the valve remains closed and no water will flow through the heater core. As the mode switch is turned, vacuum is directed through the mode switch and onto the desired vacuum actuators through different colored plastic tubing. This vacuum will activate the vacuum actuator rod which then moves a vent position door. Vacuum is vented from the vacuum actuator/plastic tube once the vacuum mode switch is turned to another position.

Temperature Door Control
The air mix doors control airflow through the heater core. They are mechanically connected to the temperature control dial at the HVAC controller via a rod, pinion and crescent gear assembly. As the temperature control switch is rotated from Cold to Hot, the air mix doors are moved to direct all or some of the air, depending on the position of the temperature control dial, within the HVAC unit through the heater core. There are 2 air mix doors that operate together to regulate airflow through the heater core. The front air mix door is connected through levers to the actuating rod which in turn is connected to the temperature switch on the HVAC controller. As the temperature switch is rotated the front air mix door is moved simultaneously with the rear air mix door via the relay rod connecting both air mix doors together.

The air mix door function is the only HVAC airflow control not to use a vacuum actuator. An actuating rod provides a mechanical connection between the HVAC controller and the HVAC unit. The rod is installed between the temperature switch mechanism and the air mix door levers. The amount of airflow through the heater core is determined by the degree of opening at the air mix door. When the temperature switch is rotated, the air mix door is opened or closed by the crescent gear pushing or pulling the actuating rod. The rod is attached to the crescent gear by a pivoting rod retainer. The assembled position of the retainer on the actuating rod is adjustable. The retainer must clamp the actuating rod at a specific location if the correct relative positions of the air mix door and temperature switch are to be maintained.

Mode Switch
The MODE switch is a rotary vacuum valve that directly applies vacuum to the appropriate vacuum actuator. Use the MODE switch in order to change the air delivery mode in the vehicle. The following modes are available:
- DEFOG
- FLOOR
- BI-LEVEL
- PANEL
- RECIRCULATION
- FRONT DEFROST

Recirculation
When the driver selects the RECIRCULATION mode, there is no fresh air entry into the vehicle. Air is delivered through the instrument panel outlets and a small amount is delivered to the floor. The plenum chamber (outside air) inlet to the HVAC unit is closed off by the recirculation doors. Interior air is drawn into the HVAC unit through the recirculation inlets by the blower motor fan, and is then forced through the cold evaporator fins. In the coldest position, the air mix doors are positioned to allow all air to bypass the heater core. In the hottest position, the air mix doors are positioned to direct all incoming air through the heater core. The air travels through the open panel door and is then directed out of the HVAC case to the panel vents.

Panel
When the driver selects the PANEL mode, air is delivered through the instrument panel outlets and a small amount is delivered to the floor. The recirculation doors are closed allowing outside air to enter and flow into the HVAC unit via the plenum chamber inlet. Air is drawn into the HVAC unit by the blower motor, and is then forced through the cold evaporator fins. In the coldest position, the air mix doors are positioned to allow all air to bypass the heater core. In the hottest position, the air mix doors are positioned to direct all incoming air through the heater core. The air travels through the open panel door and is then directed through the center and side vents. 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 panel door. The defroster actuator will retract, closing the defroster door and open the heater door through mechanical linkage.

Bi-Level
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. The recirculation doors are closed allowing outside air to enter and flow into the HVAC unit via the plenum chamber inlet. Air is drawn into the HVAC unit by the blower motor, and is then forced through the cold evaporator fins. In the coldest position, the air mix doors are positioned to allow all air to bypass the heater core. In the hottest position, the air mix doors are positioned to direct all incoming air through the heater core. The air travels through the half opened panel door and the fully opened foot door. The air is then directed through the center and side vents as well as to the floor ducts. 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
When the driver selects the FLOOR mode, air is delivered through the floor outlets with some toward the windshield and side vents. The recirculation doors are closed allowing outside air to enter and flow into the HVAC unit via the plenum chamber inlet. Air is drawn into the HVAC unit by the blower motor, and is then forced through the cold evaporator fins. In the coldest position, the air mix doors are positioned to allow all air to bypass the heater core. In the hottest position, the air mix doors are positioned to direct all incoming air through the heater core. The air travels through the foot door and is then directed to the floor ducts. 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 retracts, closing the vent door. The defroster actuator will retract, closing the defroster door and open the heater door through mechanical linkage.

Defog
When the driver selects the MIX-BLEND mode, air delivery is divided between the floor and windshield outlets. The recirculation doors are closed allowing outside air to enter and flow into the HVAC unit via the plenum chamber inlet. Air is drawn into the HVAC unit by the blower motor, and is then forced through the cold evaporator fins. In the coldest position, the air mix doors are positioned to allow all air to bypass the heater core. In the hottest position, the air mix doors are positioned to direct all incoming air through the heater core. The air travels through the open front defrost door and floor door. The air is then directed to both the front windscreen and the floor ducts. 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
When the driver selects the FRONT DEFROST mode, air is delivered to the windshield outlets. The recirculation doors are closed allowing outside air to enter and flow into the HVAC unit via the plenum chamber inlet. Air is drawn into the HVAC unit by the blower motor. This air is then forced through the cold evaporator core fins removing moisture from the air. In the hottest position, the air mix doors are positioned to direct this dehumidified incoming air through the heater core. The air travels through the open front defrost door. The heated air is then directed to the front windscreen via the front defrost outlets. By turning on the A/C system in this mode, dehumidification of incoming air will take place, front defrosting the front windscreen and side windows in a shorter period.

DEFAULT MODE
If a total loss of vacuum occurs within the system, the HVAC unit will default to the following settings. These settings will be the same in any position of the mode control switch.
- The recirculation doors will remain closed allowing outside air to enter and flow into the HVAC unit via the plenum chamber inlet
- Heated coolant will flow through the heater core regardless of the position of the temperature switch, because vacuum is required to maintain the water valve in the cold (closed) position
- The front defrost door will be positioned so that all air leaving the HVAC unit will be directed to the front defrost outlets
- The panel door and the floor door will remain closed in any position of the mode switch
- The air mix doors positions will still be determined by the temperature switch because they are controlled by mechanical linkage
- The blower fan will operate as normal