Air Delivery Description and Operation (without A/C)

Air Delivery Description and Operation (without A/C)

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.

Air Speed Control

The blower motor circulates air through the vehicle's interior. The vehicle operator determines the blower motor's speed by placing the blower motor switch in one of the following positions:

* Low
* Medium
* High

The blower motor will operate in any switch position other than OFF, as long as the ignition switch is in the RUN position. The blower motor's electrical system consists of two blower relays, a blower motor diode module, blower motor resistor assembly and a blower motor switch.

Ground is provided to the blower motor switch through the ground circuit. The switch directs the ground to the blower relays over the blower motor control circuits. Voltage is supplied to the relays through the ignition 3 voltage and battery positive voltage circuits. When the relay or relays close, power from the instrument panel fuse block is sent through the relays to the blower motor resistor assembly and then to the blower motor. The blower motor diode module prevents current from flowing through to the other blower motor control circuits when the medium or the high speed is selected.

Low Blower Speed

When the Low blower speed is selected, ground is provided to the blower motor diode module over the low blower motor control circuit. This grounds the coil side of the blower 1 and blower 2 relays. When both relays are engaged, the voltage is sent through the blower 1 relay to the blower motor resistor assembly, through the blower motor resistor assembly supply voltage circuit. Voltage is divided between 2 series resistors and is sent to the blower motor through the blower motor supply voltage circuit. The ground circuit provides a ground path for the blower motor.

Medium Blower Speed

When the Medium blower speed is selected, ground is provided to the blower 1 relay through the medium blower motor control circuit. When the coil side of the relay is grounded, voltage is supplied to the blower motor resistor assembly through the blower motor resistor assembly supply voltage circuit. Voltage is reduced by a single series resistor and sent to the blower 2 relay through the medium blower motor supply voltage circuit, and then to the blower motor through the blower motor supply voltage circuit. The ground circuit provides a ground path for the blower motor.

High Blower Speed

When the High blower speed is selected, ground is provided to the blower 2 relay through the high blower motor control circuit. When the coil side of the relay is grounded, voltage from the blower 1 relay is sent through the blower motor relay supply voltage circuit, through blower 2 relay and then to the blower motor, through the blower motor supply voltage circuit. The ground circuit provides a ground path for the blower motor.

Off

The blower motor is turned off. The temperature actuator can still be moved while in the OFF mode. When the vehicle is moving, air flowing over the vehicle increases the air pressure just ahead of the windshield. This forces air into the outside air inlet, into the HVAC assembly and out through the floor outlets.

Air Distribution

When the mode switches are pressed, the HVAC control module monitors the position of the mode door through the mode door position signal circuit. Voltage and ground are supplied to the mode actuator through the mode door control A and mode door control B circuits. The polarity is switched depending on the direction the door needs to move.

A 5-volt reference signal is sent out over the 5-volt reference circuit to the mode actuator. When a desired mode setting is selected, a variable resistor is used to determine the mode door position. That variable resistor is grounded through the low reference circuit.

If the mode actuator or wiring fails, the mode LED graph on the HVAC control module will flash. Power and ground are provided to the HVAC control module by the ignition 3 voltage, battery positive voltage and ground circuits.