Operating Modes

HVAC Actuators:

A/C Mode:

Air Flow Diagram:

Defrost Mode:

Heat Mode:

The driver can manually select different modes of operation. The modes of operation are described as follows:

Off
The blower motor and A/C compressor are turned OFF.

When the vehicle is moving, air flowing over the vehicle increases air pressure just ahead of the windshield so some air is forced into the outside air inlet, through the heater and A/C module assembly, and out the floor and windshield outlets.

Temperature control circuitry is still activated so that the heater and A/C programmer operates the air mix valve and attempts to match the inside and SET temperatures. Since the compressor is not running, system air can be warmed but not cooled.

If the RECIRC button is pressed when the system is OFF, the system will return to the last setting prior to being turned off.

Upper

MAX A/C

If system was turned OFF and this was the last setting, pressing the A/C button or RECIRC button, will return the system to this setting.

The A/C compressor is activated if outside temperature is above 6°C (43°F) and runs to keep the evaporator core at about 1°C (33°F).

The heater and A/C programmer closes the defroster door, positions the air inlet door to the recirculate position, and positions the A/C door so air is discharged through the A/C vents.

Inside air is pulled into the system by the blower and forced out the instrument panel outlets.

The heater and A/C programmer determines the proper air discharge temperature and positions the air mix door accordingly.

Norm A/C

If system was turned OFF and this was the last setting, pressing the A/C button or RECIRC button will return the system to this setting.
NORM A/C mode can be accessed by the heater and A/C programmer when it is operating in AUTO mode.

The A/C compressor is activated if outside temperature is above 6°C (43°F) and runs to keep the evaporator core at about 1°C (33°F).

The heater and A/C programmer positions the door as explained in MAX A/C; except that the air inlet door is positioned so outside air is pulled into the system by the blower.

The heater and A/C programmer determines the proper air discharge temperature and positions the air mix valve accordingly.

Lower

The heater and A/C programmer closes the defroster door, positions the air inlet door to the recirculate position, and positions the A/C door so air is discharged through the heater vents.

The heater and A/C programmer determines the proper air discharge temperature and positions the air mix valve accordingly.

UPPER and LOWER (BLEND)

The A/C compressor is activated if outside temperature is above 6°C (43°F) and runs to keep the evaporator core at about 1°C (33°F).

The heater and A/C programmer closes the defroster door, positions the air inlet door to the recirculate position, and positions the A/C door so air is discharged through the A/C vents and floor outlets.

The blower pulls outside air into the system and forces it out the floor and instrument panel outlets.

The heater and A/C programmer determines the proper air discharge temperature and positions the air mix valve accordingly.

Defog

The A/C compressor is activated if outside temperature is above 6°C (43°F) and runs to keep the evaporator core at about 1°C (33°F).

The blower pulls outside air into the system and forces it out the floor and windshield outlets.

The heater and A/C programmer determines the proper air discharge temperature and positions the air mix valve accordingly. The A/C compressor can not be turned off. Pressing the A/C button will not affect operation of this mode.

Defrost

The blower motor is turned ON and blower speed can be manually adjusted using the fan speed switch. The A/C compressor is activated if outside temperature is above 6°C (43°F) and runs to keep the evaporator core at about 1°C (33°F).

The heater and A/C programmer opens the defroster door, positions the air inlet door so the blower pulls outside air, and positions the A/C door so some air is discharged through the windshield vents.

The heater and A/C programmer determines the proper air discharge temperature and positions the air mix valve accordingly.

The A/C compressor can not be turned off. Pressing the A/C button will not effect operation of this mode.

Auto

The blower motor is turned ON and blower speed is automatically controlled by the heater and A/C programmer. The driver can override automatic blower control by pressing or turning the fan speed switch.

The heater and A/C programmer evaluates information supplied by the heater and A/C control and its network of sensors and determines which mode is required. The programmer then energizes the appropriate actuator(s) to enter that particular mode.

Information supplied to the programmer also determines whether outside air is drawn into the system (NORM A/C mode) or inside air is recirculated (MAX A/C mode).

If the last setting was AUTO and system was turned OFF, pressing either the A/C button or RECIRC button will restore the last AUTO setting.

Recirc

When recirc mode is selected, the programmer adjusts the outside air recirc actuator which positions the outside air recirc door to the recirculate position.

Recirc mode is available for operation in UPPER, LOWER and BLEND modes. Recirc is not allowed during FRONT DEFROST mode as this could cause windshield fogging.

The RECIRC function will operate for approximately ten minutes before it times out (shuts off). Additional activation can be made after time out. While RECIRC is operational any manual mode changes or ignition cycles will cancel the function, and allow outside air into the system.

Pressing the RECIRC button with the system OFF, returns the system to the last setting prior to being turned OFF.

Dual Zone

The programmer operates the driver and passenger air mix valves independently. If the passenger operates the passenger temperature control knob to request a warmer or cooler temperature on that side of the vehicle, the programmer operates the passenger air mix valve actuator to increase or decrease passenger side discharge temperature.