PCM when the evaporator temperature becomes too
cold. The PCM will then turn off the A/C Compressor
Clutch. The DRB scan tool can be used to monitor
this operation. Refer to diagnostics in this section for
evaporator temperature cycle points.
EXPANSION VALVE:
The valve is used to meter refrigerant into the
evaporator in accordance with cooling requirements.
The valve is located in front of the evaporator coil.
HIGH PRESSURE RELIEF VALVE
The valve is located at the rear of the compressor.
The valve is used to prevent excessive high system
pressure. The valve vents the system when a pres-
sure of 3445-4135 kPa (500 - 600 psi) and above is
reached. This prevents damage to the compressor
and other system components. The valve closes with
a minimum pressure of 2756 kPa (400 psi).
FILTER/DRIER
The drier is used to remove any traces of moisture
from the refrigerant system. The filter is used to sep-
arate any foreign particles from the refrigerant.
REFRIGERANT LINES
The lines are used to carry the refrigerant between
the various system components.
SERVICE GAUGE PORT
2.7 L: The high pressure gauge port is located on
the liquid line. The low pressure gauge port is
located on the suction line.
On 3.2/3.5L engines, they are located on the
compressor.
A/C REFRIGERANT LINES
The air conditioning lines used on this vehicle are
made from reinforced rubber with a nylon liner on
the inner walls. The ends of the A/C lines are made
with light weight aluminum fittings.
CAUTION: Never attempt to disconnect an A/C line
without reclaiming all refrigerant from the air condi-
tioning system. The system must be empty.
The O-rings are made from a special type of rubber
that is not affected by R-134a refrigerant. O-ring
replacement is required whenever lines are removed
and installed. Use only O-rings specified for this
vehicle. Failure to use the correct type of O-ring will
cause the connection to leak within a short period of
time.
When it is necessary to open the refrigeration sys-
tem, have everything needed to service the system
ready. The system should not be left open any longer
than necessary. Cap or plug all lines and fittings as
soon as they are opened. This will prevent the
entrance of dirt and moisture into the system. All
new lines and components should be capped or sealed
until they are ready to be used.
WARNING: AVOID BREATHING A/C REFRIGERANT
AND LUBRICANT VAPOR OR MIST. EXPOSURE MAY
IRRITATE EYES, NOSE AND THROAT. USE ONLY
APPROVED SERVICE EQUIPMENT MEETING SAE
REQUIREMENTS TO DISCHARGE R-134a SYSTEM.
IF ACCIDENTAL SYSTEM DISCHARGE OCCURS,
VENTILATE WORK AREA BEFORE RESUMING SER-
VICE.
R-134a SERVICE EQUIPMENT OR VEHICLE A/C
SYSTEM SHOULD NOT BE PRESSURE TESTED OR
LEAK TESTED WITH COMPRESSED AIR. SOME
MIXTURES OF AIR/R-134a HAVE BEEN SHOWN TO
BE COMBUSTIBLE AT ELEVATED PRESSURES.
THESE MIXTURES ARE POTENTIALLY DANGER-
OUS AND MAY RESULT IN FIRE OR EXPLOSION
CAUSING INJURY OR PROPERTY DAMAGE.
ATC IN-CAR TEMPERATURE SENSOR
The Automatic Temperature Control (ATC) In-Car
Temperature Sensor returns electrical signals to the
Body Control Module (BCM). The In-Car Tempera-
ture Sensor is used on ATC equipped vehicles only.
The In-Car Temperature Sensor is made up of two
parts. One part is the in-car sensor motor fan assem-
bly and the second part is a temperature thermistor.
The in-car sensor motor fan assembly attaches to the
back of the ATC Control head (Fig. 1). This assembly
has a small fan and a motor which draws air through
the intake on the front of the ATC control. The in-car
sensor thermistor is located inside of the ATC Con-
trol Head. Air drawn from the passenger compart-
ment by the in-car sensor motor-fan assembly, flows
over the thermistor. The in-car sensor thermistor
changes resistance with air temperature. The BCM
measures this resistance and calculates the tempera-
ture of the air drawn into the ATC Control. The ATC
system then makes adjustments to maintain the opti-
mum passenger compartment comfort. Refer to the
ATC Sensor Motor-Fan Operation table for when the
ATC Sensor is operating.
Fig. 1 ATC In-Car Temperature Sensor
300M
HEATING AND AIR CONDITIONING
24 - 3
DESCRIPTION AND OPERATION (Continued)