For 1990-2009 cars

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

• | HVAC Control Components

• | Air Speed

• | Air Delivery

• | Recirculation Operation

### HVAC Control Components

#### HVAC Control Assembly

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 battery positive and ignition 3 voltage circuits provide power to the control assembly. The temperature door is controlled by cables. The control assembly supports the following features:

Feature | Availability
--- | ---
Afterblow | No
Purge | No
Personalization | No
Actuator Calibration | No

#### Mode Actuator

The 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 HVAC control module 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.

### Air Speed

The HVAC control assembly applies voltage to the blower motor control circuit that corresponds to the selected blower speed. The resistors and the blower motor are in a series circuit. The following list represents the number of resistors in series with the blower motor per particular speed request:

• | Low speed-3 resistors

• | Medium 1 speed-2 resistors

• | Medium 2 speed-1 resistors

When the operator requests High speed, the HVAC control assembly applies voltage directly to the blower motor through the high blower motor control circuit. The resistor card has a fusible link which if blown, will require that the card be replaced.

### Air Delivery

The HVAC control module controls the mode actuator in order to distribute airflow to a desired outlet. When the mode door is moved to the defrost or mix-blend positions, the A/C compressor clutch engages and the recirculation actuator will be moved to the outside air position. The flow of air during the various modes of operation is as follows:

• | Panel - Instrument panel outlets

• | Bi-Level - Instrument panel and floor outlets

• | Floor - Floor outlets with a small amount bleed air to the defrost outlets

• | Mix-Blend - Floor and defroster outlets with a slight bleed to the instrument panel outlets

• | Defrost - Defrost outlets with a small amount of air to the side window defoggers

### Recirculation Operation

The recirculation actuator is a 2-wire bi-directional electric motor. Two control circuits enable the actuator to operate. The control circuits use either ground or a 12-volt value to co-ordinate the actuator movement. The HVAC control assembly reverses the polarity of the control circuits to move the actuator in the opposite direction. The recirculation operation can function with blower motor in either the ON or OFF position. The A/C compressor automatically comes on when recirculation is selected. Recirculation is not available in Defrost and Mix-Blend mode.