cloudy days and at night it will probably be slightly
warmer. Infrared Three-Zone Temperature Control
provides side-to-side and front-to-rear variation in
comfort temperature settings. The Infrared Three-
Zone Automatic Temperature Control fan provides a
continuously variable air flow rate to meet occupant
comfort requirements.
FRONT CONTROL PANEL
²AUTO HI/LO± This system features two sets of
automatic control logic that allow either a rapid cool-
down rate or a somewhat slower cool-down rate with
less fan noise. HI-AUTO controls the system to reach
its assigned temperature quickly with a higher fan
speed. LO-AUTO controls the system to reach its
assigned temperature somewhat slower with less fan
noise. Both modes will automatically engage auto
recirculation.
²DE-FROST± The front de-frost function is
active when the rear window defogger function is
active or when the defog/defrost mode is selected.
²RECIRC± The RECIRC button will close the
air inlet door. If the system is in auto recirc (indica-
tor being displayed automatically), pressing the man-
ual recirc button will disable the auto recirc function
until one of the auto keys are pressed or the ignition
is cycled. If Auto HI/LO is pressed while manual
recirc is active, manual recirc will be deactivated.
²REAR WINDOW DEFOGGER± Pushing the
button sends a PCI bus message to the Intelligent
Power Module which controls the Rear Window
Defogger and side view mirror (if equipped) circuitry.
The defogger function will be active for 10 minutes
and can be turned off by a switch press. The defogger
will function while the control is in the OFF mode.
²FAN/MODE± The Fan and Mode knobs have
17 manual selectable positions. Manually changing
either of the rotary knobs for mode or fan speed set-
tings makes control of that function alone manual for
as long as the ignition is on. If only one is changed
manually, the other remains under automatic control.
Pressing the HI-AUTO/LO-AUTO rocker switch
restores full automatic control.
²REAR CONTROL± When the Rear System
control knob is moved to the OFF position, there will
be a delay of approximately 1 second before the sys-
tem actually turns off. This delay is to prevent an
undesired blower dropout if the knob is moved
through OFF to the other selections.
²BLOWER DELAY TIMER± The word DELAY
is displayed at start-up to signify that the system is
waiting so that cold air will not be blowing. This tells
the operator that it is unnecessary to turn the sys-
tem off, raise the temperature setting or turn the fan
speed setting down to prevent cold air from blowing.
A countdown in minutes and seconds until the engineis warm enough to begin delivering heat to the pas-
sengers alternates with the DELAY message at 25
second intervals. This countdown is based on actual
measurement of the rate of engine coolant tempera-
ture change. During the delay time, Defrost mode is
selected and the fan operates at a low speed to keep
the windshield fog free.
REAR CONTROL PANEL
Primary control of the rear compartment unit is in
the instrument panel center stack. The rear unit con-
trol knob there allows the driver to turn the rear
unit off, allow control by the intermediate seat occu-
pants by switching to the REAR position, or provide
fully automatic control based on the temperature set-
ting shown on the front control display.
²REAR CONTROL± Selecting automatic control
of the rear unit at the instrument panel, illuminates
a Locked Padlock in the rear control panel display.
Selecting REAR activates the rear control panel and
the Padlock then appears unlocked.
²FAN KNOB± The rear fan control has Off and
AUTO positions and a range of manual speed set-
tings that override the AUTO setting.
²MODE KNOB± The mode control allows inter-
mediate seat occupants to manually override the
automatic mode and select any balance of air flow
between overhead and floor outlets from full over-
head to full floor.
²SET TEMP± The rear set temp control will
operate identical to the front controls. If the front
control rear set temp button is pressed simulta-
neously with the rear control head, then the front
control head press events shall have priority, i.e. if
the front user presses Rear Set Temp down and the
rear user presses Set Temp up, then the rear set
temp will decrease.
DIAGNOSIS AND TESTING - A/C COOL DOWN
TEST
The heater-A/C control module can perform an A/C
cool down test, which is a test performed during the
manufacturing process to confirm that the air condi-
tioning system is performing satisfactorily. This test
can also provide a quick confirmation of air condi-
tioning system performance to the service technician.
If the test is completed satisfactorily, no further ser-
vice is required. If the test is failed, proceed to the
A/C Performance Test to confirm the a/c system is
operating properly, or use a DRBIIItscan tool to
diagnose the A/C system control and distribution sys-
tems. Refer to the appropriate diagnostic informa-
tion.
24 - 4 HEATING & AIR CONDITIONINGRS
HEATING & AIR CONDITIONING (Continued)
ProCarManuals.com
Performance Temperature and Pressure
Ambient Temperature 21É C
(70É F)27É C
(80É F)32É C
(90É F)38É C
(100É F)43É C
(110É F)
Left Center Panel
Outlet Discharge Air
Temperature1to8ÉC
(34 to 46É F)3to9ÉC
(37 to 49É F)4 to 10ÉC
(39 to 50É F)6to11ÉC
(43 to 52É F)7 to 18É C
(45 to 65É F)
Discharge Pressure
(High Side Service
Port)1034 to 1724
kPa
(150 to 250
psi)1517 to 2275
kPa
(220 to 330
psi)1999 to 2620
kPa
(290 to 380
psi)2068 to 2965
kPa
(300 to 430
psi)2275 to 3421
kPa
(330 to 450 psi)
Suction Pressure (Low
Side Service Port)103 to 207 kPa
(15 to 30 psi)117 to 221 kPa
(17 to 32 psi)138 to 241 kPa
(20 to 35 psi)172 to 269 kPa
(25 to 39 psi)207 to 345 kPa
(30 to 50 psi)
DIAGNOSIS AND TESTING - HEATER
PERFORMANCE TEST
PRE-DIAGNOSTIC PREPARATIONS
WARNING: REFER TO THE APPLICABLE WARN-
INGS AND CAUTIONS FOR THIS SYSTEM BEFORE
PERFORMING THE FOLLOWING OPERATION.
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING FRONT - WARNING - HEATER PLUMB-
ING).
Check the coolant level, drive belt tension, radiator
air flow, and cooling fan operation. Start the engine
and allow it to warm up to normal temperature.
MAXIMUM HEATER OUTPUT: TEST AND ACTION
Engine coolant is provided to the heater system by
two 16 mm (5/8 inch inside diameter) heater hoses.
With the engine idling at normal running tempera-
ture, set the heater-A/C controls as follows. Temper-
ature control to full Heat, Mode control to Floor,
Blower control to the highest speed setting. Using a
test thermometer, check the air temperature coming
from the center floor outlets and compare this read-
ing to the Temperature Reference table.
TEMPERATURE REFERENCE
AMBIENT
TEMPERATUREMINIMUM FLOOR
OUTLET TEMPERATURE
CELSIUS FAHRENHEIT CELSIUS FAHRENHEIT
15.5É 60É 62.2É 144É
21.1É 70É 63.8É 147É
26.6É 80É 65.5É 150É
32.2É 90É 67.2É 153ÉIf the floor outlet air temperature is insufficient,
check that the cooling system is operating to specifi-
cations. (Refer to 7 - COOLING/ENGINE - DIAGNO-
SIS AND TESTING). Both heater hoses should be
HOT to the touch (the coolant return hose should be
slightly cooler than the supply hose). If the coolant
return hose is much cooler than the supply hose,
locate and repair the engine coolant flow obstruction
in heater system.
POSSIBLE LOCATIONS OR CAUSE OF OBSTRUCTED
COOLANT FLOW
²Pinched or kinked heater hoses.
²Improper heater hose routing.
²Plugged heater hoses or supply and return ports
at cooling system connections.
²Plugged heater core.
²Air locked heater core.
²Restrictor in backwards.
If coolant flow is verified and the heater floor out-
let temperature is insufficient, a mechanical problem
may exist.
POSSIBLE LOCATION OR CAUSE OF INSUFFICIENT HEAT
²Obstructed cowl air intake.
²Obstructed heater system outlets.
²Blend-air door not functioning properly.
TEMPERATURE CONTROL
If heater floor outlet temperature cannot be
adjusted with the heater-A/C control temperature
control lever, one of the following could require ser-
vice:
²Blend-air door binding.
²Faulty blend-air door motor.
²Improper engine coolant temperature.
²Faulty heater-A/C control.
24 - 6 HEATING & AIR CONDITIONINGRS
HEATING & AIR CONDITIONING (Continued)
ProCarManuals.com
OPERATION
The rear expansion valve solenoid is designed to
control the flow of refrigerant to the rear evaporator.
The solenoid receives fused battery current through
the rear blower motor relay on a fused rear blower
motor relay output circuit, and receives a ground
feed from the front ATC heater-A/C control module
on a TXV solenoid feed circuit. The front ATC heater-
A/C control module is programmed to control solenoid
operation. When the solenoid blocks refrigerant flow
to the rear evaporator, the resulting increase in the
refrigerant circulation rate between the condenser
and the front evaporator provides improved A/C cool-
ing performance for the front seat occupants. The
solenoid may be diagnosed using a DRBIIItscan
tool. Refer to the appropriate diagnostic information.
INFRARED TEMPERATURE
SENSOR
DESCRIPTION
The rear infrared temperature sensor consists of
an infrared transducer that is concealed behind the
lens of the rear heater-A/C control in the headliner.
This sensor is used only on models equipped with the
optional Automatic Temperature Control (ATC) heat-
ing and air conditioning system. The rear infrared
temperature sensor is integral to the rear heater-A/C
control. The infrared sensor cannot be adjusted orrepaired and, if faulty or damaged, the rear heater-
A/C control unit must be replaced.
OPERATION
The rear infrared temperature sensor provides an
independent measurement input to the Automatic
Temperature Control (ATC) heater-A/C control mod-
ule that indicates the surface temperature of the rear
seat occupants. By using a surface temperature mea-
surement, rather than an air temperature measure-
ment, the ATC system is able to adjust itself to the
comfort level as perceived by the occupant. This
allows the system to detect and compensate for other
ambient conditions affecting comfort levels, such as
solar heat gain or evaporative heat loss. The ATC
system logic responds to the infrared sensor input by
calculating and adjusting the air flow temperature
and air flow rate needed to properly obtain and
maintain the selected comfort level temperatures for
the rear seat occupants. The ATC heater-A/C control
module continually monitors the infrared sensor cir-
cuit, and will store a Diagnostic Trouble Code (DTC)
for any problem it detects. This DTC information can
be retrieved and the infrared temperature sensor
diagnosed using a DRBIIItscan tool. Refer to the
appropriate diagnostic information.
MODE DOOR ACTUATOR
DESCRIPTION
Fig. 9 Expansion Valve Solenoid
1 - SOLENOID
2 - SOLENOID CONNECTOR
3 - SEALING PLATE
4 - EXPANSION VALVE
5 - SEALING PLATE
6 - HVAC CONNECTOR
Fig. 10 Mode Door Actuator
1 - SCREW (2)
2 - MODE DOOR ACTUATOR
3 - SCREW (2)
4 - CONNECTOR
5 - BLEND DOOR ACTUATOR
6 - CONNECTOR
RSCONTROLS - REAR24-37
EXPANSION VALVE SOLENOID (Continued)
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