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 Module

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. Two integrated potentiometers control air temperature door position and blower motor speed. The integrated vacuum system controls the mode door position. The control assembly supports the following features:

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

### 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-4 resistors

• | Medium 1 speed-3 resistors

• | Medium 2 speed-2 resistors

• | Medium 3 speed-1 resistor

When the operator requests High speed, the HVAC control assembly applies voltage to the blower motor relay through the high blower motor control circuit. The voltage energizes the blower motor relay, connecting the blower motor to battery positive voltage.

### Air Delivery

#### Mode Switch

The mode switch is a rotary vacuum valve that directly applies vacuum to the appropriate vacuum actuator. Use the mode switch to change the air delivery mode in the vehicle.

#### MAX A/C-Pontiac

When the operator selects MAX A/C, the mode actuator has vacuum applied to it through the Yellow vacuum line, making the vent door open. The defrost actuator has vacuum applied to it through the Green vacuum line, making the defrost door close and the heater door open through mechanical linkage. A solenoid inside the HVAC control assembly connects the recirculation door vacuum actuator to the vacuum source. The recirculation actuator retracts, allowing air to be recirculated.

#### Vent Mode

When the operator selects VENT, the mode actuator has vacuum applied to it through the Yellow vacuum line, making the vent door open. The defrost actuator has vacuum applied to it through the Green vacuum line, making the defrost door close and the heater door open through mechanical linkage.

#### Bi-Level Mode

When the operator selects Bi-Level, the following occurs:

• | The mode actuator is in neutral position.

• | The defrost actuator has vacuum applied to it through the Green vacuum line.

• | The defrost actuator closes the defrost door, thus opening the heater door though a mechanical linkage.

• | Vacuum is bled off the mode actuator and the vent door is held stationary in the half open position.

#### Floor Mode

When the operator selects FLOOR, the mode actuator has vacuum applied to it through the Red vacuum line, pushing the vent door closed. The defrost actuator has vacuum applied to it through the Green vacuum line, pulling the defrost door closed and opening the heater door through mechanical linkage.

#### Mix-Blend Mode

When the operator selects Mix-Blend, the following occurs:

• | The mode actuator has vacuum applied to it through the Red vacuum line, pushing the vent door closed.

• | Vacuum is bled off the defrost actuator, holding the defrost door stationary in the half-open position. The heater door is also held stationary in the half-open position through mechanical linkage.

• | A/C is forced ON.

• | Recirculation is not available.

#### Defrost Mode

When the operator selects Defrost, the following occurs:

• | The mode actuator has vacuum applied to it through the Red vacuum line, pushing the vent door closed.

• | The defrost actuator has vacuum applied to it through the Blue vacuum line, pushing the defrost door open and closing the heater door through mechanical linkage.

• | A/C is forced ON.

• | Recirculation is not available.

### Recirculation Operation-Pontiac

Recirculation is only available in MAX A/C. When MAX A/C mode is selected a solenoid inside the HVAC control assembly connects the recirculation door vacuum actuator to the vacuum source. The recirculation actuator retracts, closing the recirculation door.

### Recirculation Operation-Oldsmobile

When the operator presses the Recirculation switch, a solenoid inside the HVAC control assembly connects the recirculation door vacuum actuator to the vacuum source. The recirculation actuator retracts, closing the recirculation door. The recirculation operation can function with blower motor in either the ON or OFF position. Recirculation will continue and the LED will illuminate until either outside air is selected or the next ignition cycle. Recirculation is not available in Defrost and Mix-Blend mode. The A/C compressor is engaged when in recirculation mode.