The driver can select from eight different modes of operation from the heater and the A/C control head. The HVAC can initiate two additional "purge" modes when certain conditions exist.

Select the off mode to turn off the blower motor and the A/C compressor. The control head displays the SET TEMP information for 5 seconds, then reverts to the OUTSIDE TEMP display.

While the vehicle is moving, some air is forced into the vehicle through the air intake. This air is delivered through the HVAC module and out of the Heater and Defrost ducts.

When the A/C compressor is off, the air temperature can still be adjusted. The air can be warmed, but not cooled.

In the auto mode the control head turns on the system power. The system tries to obtain the last temperature setting and the system tries to maintain that setting. The system changes the air delivery mode to automatic and the system illuminates the AUTO and AIR DELIVERY mode graphics.

The blower speed adjusts automatically as the system nears the temperature setting. The blower speed changes by pushing the blower speed button up or down. The control head displays the SET TEMP information for 5 seconds. Then the control head reverts to the OUTSIDE TEMP display and illuminates the air delivery mode graphics.

Press the MODE button to manually lock in the current air delivery setting and to stop the automatic mode control. Pressing the MODE button will delete AUTO from the digital display and the MODE graphics will be shown.

When the mode button is pushed, the control head cycles through the manual air delivery modes in the following sequence:

1. UPPER
2. LOWER
3. DEFOG
4. BILEVEL

Press this button to limit the amount of fresh air entering the vehicle. The light on the button will come on to show that the system is operating. Recirc is helpful when you are trying to cool the air quickly or trying to limit odors and just from entering the vehicle. When the system is in the AUTO mode, the system automatically selects Recirc to cool the vehicle's temperature. By pressing this button , the system will lock into the recirculated air mode. Any adjustment to the air intake must then be made manually. The Recirc mode will not operate in the front defrost mode, this helps prevent windshield and window fogging due to moisture in the vehicle.

The recirc mode function operates in the following air delivery modes:

This setting directs most of the air through the instrument panel outlets and a very small amount to the lower outlets.

This setting directs air into the vehicle in two ways. Cooler air is directed toward the upper body through the instrument panel outlets, while warmer air is directed through the lower outlets.

This setting directs most of the air to the floor area and some of the air toward the windshield and side window vents.

This setting divides the air between the windshield and lower outlets and a small amount toward the side window vents. This is useful fog appears on the windshield or side glass due to rain or snowy conditions.

Press the FRONT defrost button to quickly remove fog or frost from the windshield. This setting directs most of the air flow to the windshield and a small amount toward the lower and side window outlets. The light on the button will come on and the digital display will show the defrost mode symbol an fan speed when the front mode is being used. Pressing FRONT defrost again will return the system to the last operating mode.

If the system is in FRONT defrost when the engine is shut off, it will restart in FRONT defrost unless the engine is off for longer than 40 minuets. If the engine is off longer than 40 minuets, the system will restart in the operating mode that was set prior to FRONT defrost.

This button turns the rear defogger and heated outside mirrors on. The light on the button will come on when operating. The system automatically shuts off after approximately 10 minuets. If further defogging is desired, press the button again.

This button turns the air conditioning compressor on or off, except in the FRONT defrost mode. The light on the A/C button will come on when the compressor is operating in either the automatic or manual mode. The air conditioning may be forced off at high engine speeds. The light on the A/C button will flash if pressed when the air conditioning is not allowed to operate.

The air conditioning does not operate at temperatures below approximately 35°F to 40°F (2°C to 4°C). If the system is operating in the AUTO mode, turning the air conditioning off will delete AUTO from the digital display and show the current mode and fan settings. The AUTO button must be pressed to return to the automatic mode operation.

Press this button to provide fresh air from the outside. The light on the button will come on to show that it is operating. When in the AUTO mode, the system automatically selects outside air to control the temperature in the vehicle. By pressing OSA button, the system will lock into the fresh air mode. Any adjustment to the air intake must then be made manually. OSA should be used when trying to defrost or defog the windows to help reduce moisture inside the vehicle.

Blower Motor speed is determined by the voltage applied to the Blower Motor. This voltage varies from approximately 4 volts (low speed) to approximately 12 volts (high speed). The voltage applied to the Blower Motor is controlled by the Blower Motor Module. The Blower Motor speed can be adjusted manually by placing the Heater-A/C Control in the "AUTO" mode. The Heater-A/C Control sends blower request information to the Blower Motor Module in the form of a variable voltage signal. This voltage signal ranges from approximately 0.5 volts (for low speed) to approximately 7 volts (for high speed). An amplifier and driver circuit in the Blower Motor Module supplies voltage (4 to 12 volts) to the Blower Motor according to the request signal from the Heater-A/C Control.

The compressor for the air conditioning system is belt-driven by the engine through the A/C Compressor Clutch. The Powertrain Control Module (PCM) controls the A/C Compressor depending on the HVAC Programmer Module mode and temperature settings. The PCM controls the A/C Compressor Clutch by activating the A/C CLU micro relay 34.

When the PCM receives a A/C request from the HVAC Programmer Module through circuit 762, it activates the A/C CLU micro relay 34 through circuit 459. The battery voltage is applied from the A/C mini fuse 24 and A/C micro relay 34 to the A/C Compressor Clutch through circuit 59. Circuit 59 also carries the A/C Compressor status to the PCM. The A/C Diode prevents current flow that could damage A/C Compressor Clutch components. The A/C Compressor Clutch is grounded through circuit 150 to Splice Pack #100, SP100.

The PCM uses the A/C Refrigerant Pressure Sensor to control refrigerant pressure. If the refrigerant pressure is too high (i.e., could cause engine overheating), the PCM disengages the A/C Compressor Clutch. The A/C Refrigerant Pressure Sensor sends refrigerant pressure data to the PCM through circuit 380. Circuit 407 supplies the A/C Refrigerant Pressure Sensor with ground voltage, and circuit 474 supplies 5V reference voltage.