HVAC Control Components through Air Speed

AIR DELIVERY DESCRIPTION AND OPERATION
The air delivery description and operation are divided into 3 areas:
- HVAC Control Components
- Air Speed
- Air Delivery

HVAC CONTROL COMPONENTS
The HVAC control assembly is a non-class 2 device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The HVAC unit is operated manually by a combination of electrical, mechanical and vacuum components. The case is of a 4-piece, plastic construction. The front and rear housing are assembled without the use of any fasteners. The front housing clips over the rear housing at 6 locations. Two equally sized recirculation doors are used to control airflow into the HVAC unit. Two air mix doors are used to control the airflow through the heater core. A single door is used to control airflow to the front defrost, floor and panel outlets. All doors excluding the air mix doors are vacuum operated. The air mix doors are operated mechanically. The blower motor/fan assembly, blower motor resistor, heater core and evaporator are all contained within the HVAC case. A vacuum tank is mounted to the left side of the case. Four externally mounted vacuum actuators are used to provide the selected ventilation modes. Contained within this assembly is a printed circuit board retained within the rear housing. Attached to the back of the rear housing are the following components:
- Water valve vacuum switch for water valve control/heater core flow
- Mode switch vacuum valve for operation of the HVAC vacuum actuators/doors
- Pinion and crescent gear for mechanical actuation of the water valve vacuum switch and HVAC air mix doors
- Electrical switch/connector for blower fan operation
- Electrical connector for illumination and A/C and heated rear window switching

All of these items, except the LED, A/C and heated rear window electrical connector, are removable from the rear housing. The illumination, A/C and heated rear window electrical connector is bonded to the printed circuit board. There are no replaceable bulbs contained within the unit. Five LEDs provide the necessary illumination. If an LED fails to function, the printed circuit board must be replaced. Individually serviced components are the water valve vacuum switch, the mode switch vacuum valve and the air mix door rod retainer. The 3 rotary switches and the front housing are serviced as a unit.

HVAC SWITCHES
The HVAC control assembly contains the following switches:

A/C Switch
The A/C switch is located at the bottom of the blower fan rotary switch. With the blower fan operating, push the A/C button once. The A/C indicator lamp will illuminate, and the A/C compressor will engage. Push the A/C button again. The A/C indicator lamp will extinguish, and the A/C compressor will disengage. Turning the blower fan to the OFF position will also cause the A/C indicator lamp to extinguish and the A/C compressor to disengage.

Rear Defogger Switch
The rear defogger switch is located at the bottom of the mode control switch. Push the rear defogger button once. The indicator lamp will illuminate, and the rear defogger window element will heat up. After 15 minutes the rear defogger will automatically turn OFF. To reactivate the rear defogger, push the button again. This will turn ON the rear defogger for another 15 minutes.

Blower Fan Switch
Four blower fan speeds are available. A fan speed must be selected before the A/C system can be engaged. The fan is in the OFF position when the indicator light is aligned with the fan symbol.

Temperature Control
The temperature control is connected via a rod and levers to the air mix doors at the HVAC case. The air mix doors control the amount of incoming air flowing through the heater core, in accordance with the selected cabin temperature. This regulates the amount of heated air mixing with the unheated or air conditioned air. The heater water valve is held in the closed position by vacuum generated by the engine. When the third detent is selected from the full cold position via the temperature control, the water valve vacuum switch located on the rear of the HVAC controller is activated and the vacuum line to the water valve is vented. This allows hot water to flow into the heater core and subsequent heating of the vehicle cabin.

AIR SPEED

Blower Motor and Fan
The blower motor draws air from the plenum chamber and circulates the air through the vehicle's interior. The vehicle operator determines the blower motor's speed by rotating the blower motor switch manually. The blower motor will only operate if the blower motor switch is in any 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 unit. The blower motor is housed in the blower case which is located behind the right side of the instrument panel. To provide the different fan speeds a resistor block consisting of 3 resistors contained within a ceramic heat sink is wired into the blower motor circuit.

Blower Circuit
The blower circuit consists of the following components:
- Blower Motor
- Blower Motor Switch
- Blower Motor Resistor
- Blower Relay
- Blower Inhibit Relay

The blower motor receives battery voltage through the Blower Fan fuse at all times. An additional 30-amp blade type fuse is fitted at the blower motor to protect the blower motor circuitry. The blower motor is provided a path to ground in speeds 1, 2 , and 3, through the blower resistor, through the blower switch, through the closed contacts of the blower inhibit relay to SP100 and G102. In high speed, the blower motor is provided a path to ground through the closed contacts of the blower relay to SP1OO and G102. The blower motor speed is maintained by controlling the voltage potential to the blower motor. This is achieved by increasing or decreasing the resistance within the blower motors ground path.

The blower motor switch receives power through the Heated Rear Window, HVAC and Instruments fuse when the ignition switch is in the RUN position. Ground is provided when the blower inhibit relay is energized.

The coil side of the blower inhibit relay receives ignition voltage through the Heated Rear Window, HVAC and Instruments fuse when the ignition switch is in the RUN position. The coil side and the switch side of the blower inhibit relay are permanently grounded at SP1OO and G102. When the blower inhibit relay is energized, a ground path is provided to the blower switch for all blower speeds.

The coil side of the blower relay receives battery voltage through the Heated Rear Window fuse at all times. When the blower switch is in the HIGH position, the coil of the blower relay is provided a path to ground through the high speed contacts of the blower switch, through the closed switch contacts of the blower inhibit relay to SP100 and G102. This energizes the blower relay and provides the blower motor with a direct path to ground through the closed contacts of the blower relay to SP1OO and G102.

Low Blower Speed
When the Low blower speed is selected, battery voltage is applied to the blower motor through the Blower Fan fuse supply voltage circuit. Voltage is decreased through 3 series resistors to achieve the desired blower speed. The blower motor is grounded through the low speed contacts of the blower motor switch, through the closed switch contacts of the blower inhibit relay to SP100 and G102. A blower ON signal is provided to the body control module (BCM) in low speed only.

Medium Blower Speeds
When the Medium 1 blower speed is selected, battery voltage is applied to the blower motor through the Blower Fan fuse supply voltage circuit. Voltage is decreased through 2 series resistors to achieve the desired blower speed. The blower motor is grounded through the low speed contacts of the blower motor switch, through the closed switch contacts of the blower inhibit relay to SP1OO and G102.

When the Medium 2 blower speed is selected, battery voltage is applied to the blower motor through the Blower Fan fuse supply voltage circuit. Voltage is decreased through 1 series resistors to achieve the desired blower speed. The blower motor is grounded through the low speed contacts of the blower motor switch, through the closed switch contacts of the blower inhibit relay to SP100 and G102.

High Blower Speed
When the High blower speed is selected, battery voltage is applied to the blower motor through the through the Blower Fan fuse supply voltage circuit. When the blower switch is in the HIGH position, the coil of the blower relay is provided a path to ground through the high speed contacts of the blower switch, through the closed switch contacts of the blower inhibit relay to SP1OO and G102. This energizes the blower relay and provides the blower motor with a direct path to ground by removing the blower motor resistor from the circuit. The blower motor grounds through the closed contacts of the blower relay to SP1OO and G102.

OFF
When the blower switch is in the OFF position, any A/C request will be cancelled and the A/C indicator will turn OFF. 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.