allows one temperature setting for the entire vehicle.
The full range of temperatures that the system can
produce are available by rotating the temperature
control located in control panel.

The

control

panel

and

integral

computer

mounted in the instrument panel.

DESCRIPTION - DUAL ZONE

A manual Dual Zone Heating and Air Conditioning

system allows completely independent side-to-side
tempeture control of the discharge air.

The control panel and integral computer is located

in the instrument panel.

The instrument panel mounted control and inte-

gral computer contains:

• a power button which allows the system to be

completely turned off. Contains an LED that illumi-
nates to show when the function is operational.

• rear window defogger on/off switch. Contains an

LED that illuminates to show when the function is
operational.

• slide controls for completely independent side-to-

side temperature control of the discharged air. The
full range of temperature that the system can pro-
duce in any mode is available on either side of the

vehicle by independently positioning the slide con-
trols on the instrument panel.

• air recirculation on/off switch. The Recirculate

button contains an LED that illuminates to show
when the function is in operation.

• air conditioning on/off switch. The Snowflake

button contains an LED that illuminates to shown
when the function is in operation.

• rotary knob for fan speed selection.

• a rotary knob for mode control.

DESCRIPTION - MANUAL THREE ZONE

The fully adjustable Three-Zone front and rear

heating and air conditioning system allows interme-
diate seat passengers the ability to regulate air tem-
perature as well as fan speed. All controls are
identified by ISO graphic symbols.

FRONT CONTROL PANEL

The front control panel and integral computer is

mounted in the instrument panel.

The instrument panel mounted control and inte-

gral computer contains:

• a power button which allows the system to be

completely turned off.

• rear window defogger on/off switch.

• slide controls for completely independent side-to-

side temperature control of the discharge air. The full
range of temperature that the system can produce in
any mode is available on either side of the vehicle by
independently positioning the slide controls on the
instrument panel.

HEATING & AIR CONDITIONING

24 - 1

• air recirculation button. The Recirculate button

contains an LED that illuminates to show when the
function is in operation.

• an air conditioning button that allows the com-

pressor to be turned on/off. The Snowflake button
contains an LED that illuminates to shown when the
function is in operation.

• rotary knobs for front and rear fan speed selec-

tion.

• a rotary knob for mode control.

REAR CONTROL PANEL

A rear control panel centrally mounted on the

headliner has a rotary adjustment for temperature
and fan speed control of the rear unit by intermedi-
ate seat passengers when the front control rear knob
is set to the rear position.

DESCRIPTION - AUTOMATIC TEMPERATURE
CONTROL

The Automatic Temperature Control (ATC) allows

occupants to select a comfort temperature, which is
the perceived temperature level not the actual pas-
senger compartment air temperature.

The

Automatic

Temperature

Control

system

includes a dust and odor air filter. The filter element
is the same size as the air conditioning evaporator to
ensure ample capacity. A door at the base of the
heater and air conditioning housing below the glove
box provides easy access to the filter element.

The ATC computer utilizes integrated circuitry and

information carried on the Programmable Communi-
cations Interface (PCI) data bus network to monitor
many sensors and switch inputs throughout the vehi-
cle. In response to those inputs, the internal circuitry
and programming of the ATC computer allow it to
control electronic functions and features of the ATC
system. The inputs to the ATC computer are:

• Vehicle Speed/Engine RPM – The ATC com-

puter monitors engine RPM, vehicle speed and Man-
ifold Absolute Pressure information from the PCM.

• Coolant Temperature – ATC computer moni-

tors Coolant temperature received from the PCM and
converts it to degrees Fahrenheit.

• Ambient Temperature – ATC computer moni-

tors Ambient temperature from the Compass Mini
Trip Computer (CMTC) and converts it to degrees
Fahrenheit.

• Engine Miscellaneous Sensor Status – ATC

computer monitors A/C disable information from the
PCM.

• Refrigerant Pressure – ATC computer moni-

tors Barometric Pressure, Intake Air Temperature,
High Side Pressure and Methanol Content as broad-
cast by the PCM.

• Door Ajar Status – The ATC computer moni-

tors Driver Front Door, Passenger Front Door, Left
Rear Door, Right Rear Door and Liftgate ajar infor-
mation, as identified by the Body Control Module
(BCM), to determine if all in-car temperatures should
be maintained.

• Dimming – The ATC computer monitors dim-

ming status from the BCM to determine the required
level of brightness and will dim accordingly.

• Vehicle Odometer – The ATC computer moni-

tors the vehicle odometer information from the BCM
to prevent flashing the VF tube icons if the manual
motor calibration or manual cool down tests have
failed. Flashing of the display icons will cease when
the vehicle odometer is greater than 3 miles.

• English/Metric – The ATC computer monitors

the English/Metric information broadcast by the
CMTC. The set temp displays for both the front and
rear control heads will be set accordingly.

• Vehicle Identification Number – The ATC

computer monitors the last eight characters of the
VIN broadcast by the PCM and compares it to the
information stored in EEPROM. If it is different, the
new number will be stored over the old one and a
motor calibration shall be initiated.

• A/C System Information – The ATC computer

will send a message for Evaporator Temperature too
Low, Fan Blower Relay status, Evaporator Sensor
Failure, Rear Window Defogger Relay and A/C Select.

FRONT CONTROL PANEL

The front control panel and integral computer is

mounted in the instrument panel.

The instrument panel mounted control and inte-

gral computer contains:

• A power button which allows the system to be

completely turned off. The display is blank when the
system is off.

• Three rocker switches that select comfort tem-

peratures from 15° to 30° C (59° to 85° F), which are
shown in the vacuum-fluorescent digital control dis-
play. If the set temp is 59 and the down button is
pressed, the set temp value will become 55 but the
display will show LO. If the set temp is 85 and the
up button is pressed, the set temp value will become
90 but the display will show HIGH. Temperatures
can be displayed in either metric or Fahrenheit,
which is controlled from the overhead console.

• A rocker switch that selects a cool-down rate.

LO-AUTO or HI-AUTO are displayed when the sys-
tem is in automatic operation.

• A defroster button which turns on the defroster

independently

during

full

automatic

control.

defroster symbol illuminates in the display when the
button is pressed.

24 - 2

HEATING & AIR CONDITIONING

HEATING & AIR CONDITIONING (Continued)

• Air recirculation button. A Recirculation symbol

appears in the display when the button is pressed, or
when the system exceeds 80 percent circulated air
under automatic control due to high air conditioning
demand.

• Rear window defogger on/off switch. A graphic

symbol shows when the defroster is on.

• An air conditioning button that allows the com-

pressor to be turned off. A Snowflake symbol is illu-
minated when air conditioning is on, whether under
manual or automatic control.

• Rotary knob for front fan speed selection can

override the automatic controls. LEDs surrounding
the knob show the current setting.

• Rotary knob for control of the Rear system.

• A rotary knob for mode control can override the

automatic controls. LEDs surrounding the knob show
the current setting.

• Computer logic remembers the settings of the

controls when the ignition is turned off and retains
those settings after a restart. If the system is off
when the ignition is turned off it will be off when the
engine is restarted, etc.

• Computer logic provides variable air recircula-

tion under high temperature and humidity condi-
tions. Because recirculation is generally accompanied
by increased fan noise, the proportion of recirculated
to outside air gradually approaches full recirculation
over a broad temperature range.

• Computer logic enables additional heat for diesel

equipped vehicles via a supplemental diesel heater.

REAR CONTROL PANEL

A rear control panel centrally mounted on the

headliner includes a vacuum-flourescent digital dis-
play, a rocker control for temperature and rotary con-
trols for adjustment of mode and fan speed control of
the rear unit by intermediate seat passengers.

OPERATION

OPERATION - DUAL ZONE

• The mode control knob enables continously vari-

able proportioning of air flow between modes but has
detents adjacent to each icon.

• The blower control provides five separate speeds.

• When the fan is off, the HVAC computer closes

the recirculation door to prevent outside air from
entering the passenger compartment.

• Interior air may be recirculated to speed up

heating or cooling in all modes except defrost and
mix by pressing the Recirculate button on the control
panel.

• To reduce humidity for rapid defogging the A/C

compressor runs automatically in modes from “mix’

to full defrost when outside temperatures are above
freezing.

• Air conditioning is available in any mode by

pressing the snowflake, A/C on/off, button.

OPERATION - MANUAL THREE ZONE

FRONT CONTROL PANEL

• Primary control of the rear compartment unit is

on the instrument panel. This control allows the
driver to set the rear compartment fan speed, to turn
the rear unit off, or to give control to the intermedi-
ate seat occupants by switching to the REAR posi-
tion. When the rear unit is controlled from the
instrument panel, rear air temperature is based on
the driver-side temperature control position, and the
mode (floor or overhead air) is based on the front
control’s mode position.

• The mode control knob enables continously vari-

able proportioning of air flow between modes but has
detents adjacent to each icon.

• The blower control provides five separate speeds

and Off. When the fan is off, the HVAC computer
closes the recirculation door to prevent outside air
from entering the passenger compartment.

• Interior air may be recirculated to speed up

heating or cooling in all modes exccept defrost and
mix by pressing the Recirculate button on the control
panel.

• To reduce humidity for rapid defogging the A/C

compressor runs automatically in modes from “mix’
to full defrost when outside temperatures are above
freezing.

• Air conditioning is available in any mode by

pressing the snowflake, A/C on/off, button.

REAR CONTROL PANEL

With the rear control active, temperature selection

dictates indirectly the mode (floor or overhead air) of
the rear unit: a low temperature setting directs flow
to the overhead outlets and a high temperature set-
ting to the floor.

OPERATION - THREE ZONE ATC

Comfort temperature or perceived temperature is

affected by air flow, sun impinging on exposed skin,
etc. The air temperature may be higher or lower than
the comfort temperature. Two infrared sensors, in the
instrument panel center stack i measure the temper-
ature of the occupants to determine their comfort
level relative to the selected comfort temperature.
The HVAC computer in the control module adjusts
the air flow rate and temperature to maintain the
customer-perceived comfort temperature. The air
temperature in the passenger compartment at any
time may be slightly higher or lower than the com-

HEATING & AIR CONDITIONING

24 - 3

HEATING & AIR CONDITIONING (Continued)

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