For 1990-2009 cars

The air delivery description and operation is divided into 4 areas:

• | HVAC Control Components

• | Air Speed

• | Air Distribution

• | 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. An ignition 3 voltage circuit provides power to the control assembly. The air temperature, mode and recirculation actuator are electrically controlled. The control assembly does not support the following features:

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

### Air Speed

B+ is supplied to the blower motor through the HVAC/PK3+ relay when the ignition is in the RUN position. The HVAC control assembly applies a ground 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 a direct ground to the blower motor.

### Air Distribution

#### Mode Actuator

The mode actuator is a 5-wire bi-directional electric motor that incorporates a feedback potentiometer. Low reference, control A , control B, 5-volt reference and position signal circuits enable the actuator to operate. Two control circuits enable the actuator to operate. The control circuits use either ground or a 12-volt value to coordinate the actuator movement. The HVAC control assembly reverses the polarity of the control circuits to move the actuator in the opposite direction. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door position signal between 0-5 volts.

The HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted value, the control circuits are energized to rotate to reach the commanded value. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module opens the control circuits.

### 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 coordinate 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. Recirculation is not available in Defrost and Mix-Blend mode.