2001 DODGE RAM jump start

SHIFT INDICATOR (TRANSFER
CASE)
DESCRIPTION
A four-wheel drive indicator is standard equipment
on all instrument clusters. However, on vehicles not
equipped with the optional four-wheel drive system,
this indicator is mechanically disabled. The four-
wheel drive indicator is located near the lower edge
of the instrument cluster overlay, to the right of cen-
ter. The four-wheel drive indicator consists of a sten-
cilled cutout of the text ª4WDº in the opaque layer of
the instrument cluster overlay. The dark outer layer
of the overlay prevents the indicator from being
clearly visible when it is not illuminated. An amber
lens behind the cutout in the opaque layer of the
overlay causes the ª4WDº text to appear in amber
through the translucent outer layer of the overlay
when the indicator is illuminated from behind by a
Light Emitting Diode (LED) soldered onto the instru-
ment cluster electronic circuit board. The four-wheel
drive indicator is serviced as a unit with the instru-
ment cluster.
OPERATION
The four-wheel drive indicator lamp gives an indi-
cation to the vehicle operator that a four-wheel drive
operating mode is engaged. The indicator will be illu-
minated when either high range (4H) or low range
(4L) have been selected with the transfer case shift
lever. This indicator is controlled by a transistor on
the instrument cluster circuit board based upon the
cluster programming, and a hard wired input from
the four-wheel drive switch on the front axle discon-
nect housing. The four-wheel drive indicator Light
Emitting Diode (LED) receives battery current on the
instrument cluster electronic circuit board through
the fused ignition switch output (st-run) circuit
whenever the ignition switch is in the On or Start
positions; therefore, the lamp will always be off when
the ignition switch is in any position except On or
Start. The LED only illuminates when it is switched
to ground by the instrument cluster transistor.
The four-wheel drive switch is connected in series
between ground and the four-wheel drive switch
sense input to the instrument cluster. For further
information on the transfer case and the transfer
case operating ranges, (Refer to 21 - TRANSMIS-
SION/TRANSAXLE/TRANSFER CASE - OPERA-
TION. For further information on the front axle
disconnect mechanism, (Refer to 3 - DIFFERENTIAL
& DRIVELINE/FRONT AXLE/AXLE VACUUM
MOTOR - OPERATION). The four-wheel drive switch
input to the instrument cluster circuitry can be diag-nosed using conventional diagnostic tools and meth-
ods.
DIAGNOSIS AND TESTING - FOUR-WHEEL
DRIVE INDICATOR
The diagnosis found here addresses an inoperative
four-wheel drive indicator condition. If the problem
being diagnosed is related to indicator accuracy, be
certain to confirm that the problem is with the indi-
cator and not with a damaged or inoperative front
axle disconnect mechanism. (Refer to 3 - DIFFEREN-
TIAL & DRIVELINE/FRONT AXLE/AXLE VACUUM
MOTOR - DIAGNOSIS AND TESTING). If no front
axle disconnect problem is found, the following proce-
dure will help locate a short or open in the four-
wheel drive switch input to the instrument cluster.
Refer to the appropriate wiring information. The wir-
ing information includes wiring diagrams, proper
wire and connector repair procedures, details of wire
harness routing and retention, connector pin-out
information and location views for the various wire
harness connectors, splices and grounds.
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE AIRBAG SYSTEM BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, OR INSTRUMENT PANEL COMPONENT
DIAGNOSIS OR SERVICE. DISCONNECT AND ISO-
LATE THE BATTERY NEGATIVE (GROUND) CABLE,
THEN WAIT TWO MINUTES FOR THE AIRBAG SYS-
TEM CAPACITOR TO DISCHARGE BEFORE PER-
FORMING FURTHER DIAGNOSIS OR SERVICE. THIS
IS THE ONLY SURE WAY TO DISABLE THE AIRBAG
SYSTEM. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
INDICATOR DOES NOT ILLUMINATE WITH FOUR-WHEEL
DRIVE MODE SELECTED
(1) Disconnect and isolate the battery negative
cable. Disconnect the engine wire harness connector
for the four-wheel drive switch from the switch con-
nector receptacle. Check for continuity between the
ground circuit cavity of the engine wire harness con-
nector for the four-wheel drive switch and a good
ground. There should be continuity. If OK, go to Step
2. If not OK, repair the open ground circuit to ground
(G100) as required.
(2) Reconnect the battery negative cable. Turn the
ignition switch to the On position. Install a jumper
wire between the 4WD switch sense circuit cavity of
the engine wire harness connector for the four-wheel
drive switch and a good ground. The four-wheel drive
indicator should light. If OK, replace the faulty four-
wheel drive switch. If not OK, go to Step 3.
BR/BEINSTRUMENT CLUSTER 8J - 29

er-up mode will also apply if the battery goes dead
while the system is armed, and battery jump-starting
is attempted. The engine no-run feature will prevent
the engine from starting until the alarm system has
been actively or passively disarmed. The VTSS will
be armed until the technician or vehicle operator has
actively or passively disarmed the alarm system. If
the VTSS is in the disarmed mode prior to a battery
disconnect or failure, it will remain disarmed after
the battery is reconnected or replaced, or if jump-
starting is attempted.
TAMPER ALERT
The VTSS tamper alert feature will sound the horn
three times upon disarming, if the alarm was trig-
gered and has since timed-out (about fifteen min-
utes). This feature alerts the vehicle operator that
the VTSS alarm was activated while the vehicle was
unattended.
DIAGNOSIS AND TESTING - VEHICLE THEFT
SECURITY SYSTEM
The VTSS-related hard wired inputs to and out-
puts from the high-line or premium Central Timer
Module (CTM) may be diagnosed and tested using
conventional diagnostic tools and procedures. Refer
to the appropriate wiring information. The wiring
information includes wiring diagrams, proper wire
and connector repair procedures, further details on
wire harness routing and retention, as well as pin-
out and location views for the various wire harness
connectors, splices and grounds.
However, conventional diagnostic methods may not
prove conclusive in the diagnosis of the CTM, the
Powertrain Control Module (PCM), or the Chrysler
Collision Detection (CCD) data bus network. In order
to obtain conclusive testing of the VTSS, the CTM,
the PCM, and the CCD data bus network must also
be checked. The most reliable, efficient, and accurate
means to diagnose the VTSS requires the use of a
DRBIIIž scan tool. Refer to the appropriate diagnos-
tic information. The DRBIIIž scan tool can provide
confirmation that the CCD data bus network is func-
tional, that all of the electronic modules are sending
and receiving the proper messages over the CCD
data bus, and that these modules are receiving the
proper hard wired inputs and responding with the
proper hard wired outputs needed to perform their
functions. See the ªVehicle Theft Security Systemº
menu item on the DRBIIIž scan tool.
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE AIRBAG SYSTEM BEFORE
ATTEMPTING ANY STEERING WHEEL, STEERING
COLUMN, OR INSTRUMENT PANEL COMPONENT
DIAGNOSIS OR SERVICE. DISCONNECT AND ISO-LATE THE BATTERY NEGATIVE (GROUND) CABLE,
THEN WAIT TWO MINUTES FOR THE AIRBAG SYS-
TEM CAPACITOR TO DISCHARGE BEFORE PER-
FORMING FURTHER DIAGNOSIS OR SERVICE. THIS
IS THE ONLY SURE WAY TO DISABLE THE AIRBAG
SYSTEM. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
VTSS INDICATOR
DESCRIPTION
The Vehicle Theft Security System (VTSS) indica-
tor consists of a red Light-Emitting Diode (LED)
located on the electronic circuit board of the Compass
Mini-Trip Computer (CMTC) within the overhead
console. The LED extends through a hole in the
CMTC lens located near the forward end of the over-
head console housing near the windshield.
The VTSS indicator cannot be adjusted or repaired
and, if faulty or damaged, the entire CMTC unit
must be replaced. (Refer to 8 - ELECTRICAL/OVER-
HEAD CONSOLE/COMPASS/MINI-TRIP COM-
PUTER - DESCRIPTION).
OPERATION
The Vehicle Theft Security System (VTSS) indica-
tor gives a visible indication of the VTSS arming sta-
tus. One side of Light-Emitting Diode (LED) in the
VTSS indicator is connected to battery current
through a fused B(+) circuit and a fuse in the Junc-
tion Block (JB), so the indicator remains functional
regardless of the ignition switch position. The other
side of the LED is hard wired to the Central Timer
Module (CTM), which controls the operation of the
VTSS indicator by pulling this side of the LED cir-
cuit to ground. When the VTSS arming is in
progress, the CTM will flash the LED rapidly on and
off for about fifteen seconds. When the VTSS has
been successfully armed, the CTM will flash the LED
on and off continually at a much slower rate until
the VTSS has been disarmed. The VTSS indicator
can be diagnosed using conventional diagnostic tools
and methods.
DIAGNOSIS AND TESTING - VTSS INDICATOR
The diagnosis found here addresses an inoperative
Vehicle Theft Security System (VTSS) indicator con-
dition. If the problem being diagnosed is related to
indicator accuracy, be certain to confirm that the
problem is with the indicator and not with an inop-
erative VTSS. (Refer to 8 - ELECTRICAL/VEHICLE
THEFT SECURITY SYSTEM- DIAGNOSIS AND
BR/BEVEHICLE THEFT SECURITY 8Q - 3
VEHICLE THEFT SECURITY (Continued)

8W-02 COMPONENT INDEX
Component Page
4WD Switch.......................... 8W-31
A/C Compressor Clutch Relay............ 8W-42
A/C Compressor Clutch................. 8W-42
A/C-Heater Control.................... 8W-42
A/C Heater Temperature Select........... 8W-42
A/C High Pressure Switch............... 8W-42
A/C Low Pressure Switch................ 8W-42
Accelerator Pedal Position Sensor......... 8W-30
Aftermarket Center High Mounted
Stop Lamp......................... 8W-51
Aftermarket Trailer Tow Connector........ 8W-54
Airbag Control Module.................. 8W-43
Ambient Temperature Sensor............ 8W-49
Ash Receiver Lamp.................... 8W-44
Automatic Day/Night Mirror............. 8W-49
Automatic Shut Down Relay............. 8W-30
Auxiliary Battery...................... 8W-20
Back-Up Lamp Switch.................. 8W-51
Back-Up Lamps....................... 8W-51
Battery Temperature Sensor............. 8W-30
Battery............................. 8W-20
Blend Door Actuator................... 8W-42
Blower Motor Relay.................... 8W-42
Blower Motor Resistor Block............. 8W-42
Blower Motor......................... 8W-42
Brake Lamp Switch.................... 8W-51
Brake Pressure Switch............... 8W-34, 35
Bypass Jumper....................... 8W-21
Camshaft Position Sensor............... 8W-30
Capacitor......................... 8W-10, 30
Cargo Lamps......................... 8W-44
Center High Mounted Stop Lamps........ 8W-51
Center Identification Lamp.............. 8W-50
Central Timer Module.................. 8W-45
Cigar Lighter......................... 8W-41
Circuit Breakers...................... 8W-12
Clockspring.................. 8W-33, 41, 43, 47
Clutch Pedal Position Switch............. 8W-21
Combination Flasher................... 8W-52
Controller Antilock Brake............ 8W-34, 35
Crankshaft Position Sensor.............. 8W-30
Cummins Bus........................ 8W-18
Cup Holder Lamp..................... 8W-44
Cylinder Lock Switches................ 8W-39
Data Link Connector................... 8W-18
Daytime Running Lamp Module.......... 8W-50
Dome Lamp.......................... 8W-44
Door Ajar Switches.................... 8W-45
Door Lock Motors..................... 8W-61
Door Window/Lock Switches.......... 8W-60, 61
Driver Airbag......................... 8W-43
Duty Cycle EVAP/Purge Solenoid......... 8W-30Component Page
Electric Brake Provision................ 8W-54
Engine Control Module.............. 8W-30, 70
Engine Coolant Temperature Sensor....... 8W-30
Engine Oil Pressure Sensor.............. 8W-30
Engine Starter Motor Relay.............. 8W-21
Engine Starter Motor................... 8W-21
Fender Lamp......................... 8W-51
Fog Lamp Indicator.................... 8W-50
Fog Lamp Relay....................... 8W-50
Fog Lamp............................ 8W-50
Fuel Heater Relay..................... 8W-30
Fuel Heater.......................... 8W-30
Fuel Injection Pump................... 8W-30
Fuel Injectors......................... 8W-30
Fuel Transfer Pump.................... 8W-30
Fuses (JB)........................... 8W-12
Fuses (PDC).......................... 8W-10
Fusible Link....................... 8W-20, 30
Generator............................ 8W-20
Glove Box Lamp And Switch............. 8W-44
Grounds............................. 8W-15
Headlamp Beam Select Switch........... 8W-50
Headlamp Switch...................... 8W-50
Headlamp........................... 8W-50
Heated Mirror Relay................... 8W-62
Heated Mirror Switch.................. 8W-62
Heated Seat Cushions.................. 8W-63
Heated Seat Relay..................... 8W-12
Heated Seat Switches.................. 8W-63
High Beam Indicator................... 8W-40
High Note Horn....................... 8W-41
Horn Relay.......................... 8W-41
Horn Switch.......................... 8W-41
Idle Air Control Motor.................. 8W-30
Ignition Coil 4-Pack.................... 8W-30
Ignition Coil 6-Pack.................... 8W-30
Ignition Coil.......................... 8W-30
Ignition Switch....................... 8W-10
Instrument Cluster.................... 8W-40
Intake Air Heater Relays................ 8W-30
Intake Air Heater..................... 8W-30
Intake Air Temperature Sensor........... 8W-30
Intermittent Wiper Switch............... 8W-53
Joint Connectors . . 8W-10, 12, 15, 30, 31, 34, 35, 40,
44, 45, 51, 53, 70
Junction Block........................ 8W-12
Leak Detection Pump.................. 8W-30
License Lamp......................... 8W-51
Low Note Horn....................... 8W-41
Lumbar Motors....................... 8W-63
Manifold Absolute Pressure Sensor........ 8W-30
Manifold Air Pressure Sensor............ 8W-30
BR/BE8W-02 COMPONENT INDEX 8W - 02 - 1

8W-21 STARTING SYSTEM
Component Page
Auxiliary Battery.................... 8W-21-2
Battery............................ 8W-21-2
Bypass Jumper...................... 8W-21-2
Clutch Pedal Position Switch........... 8W-21-2
Engine Starter Motor................. 8W-21-2
Engine Starter Motor Relay............ 8W-21-2Component Page
Fuse 9 (PDC)....................... 8W-21-2
G105.............................. 8W-21-3
Ignition Switch...................... 8W-21-2
Park/Neutral Position Switch........... 8W-21-3
Power Distribution Center............. 8W-21-2
Powertrain Control Module............. 8W-21-3
BR/BE8W-21 STARTING SYSTEM 8W - 21 - 1

BLOWER MOTOR-2WAY
CAV CIRCUIT FUNCTION
1 C1 12DG BLOWER MOTOR FEED
2 C7 12BK/TN HIGH SPEED BLOWER MOTOR
BLOWER MOTOR RESISTOR BLOCK - BLACK 4 WAY
CAV CIRCUIT FUNCTION
1 C7 12BK/TN HIGH SPEED BLOWER MOTOR
2 C6 14LB M2 SPEED BLOWER MOTOR
3 C5 16LG M1 SPEED BLOWER MOTOR
4 C4 16TN LOW SPEED BLOWER MOTOR
BRAKE LAMP SWITCH-6WAY
CAV CIRCUIT FUNCTION
1 V40 22WT/PK BRAKE SWITCH SENSE
2 Z2 22BK/LG GROUND
3 V32 22YL/RD SPEED CONTROL SUPPLY
4 V30 22DB/RD SPEED CONTROL BRAKE SWITCH OUTPUT
5 L50 16WT/TN BRAKE LAMP SWITCH OUTPUT
6 F32 16PK/DB FUSED B(+)
BRAKE PRESSURE SWITCH - BLACK 2 WAY
CAV CIRCUIT FUNCTION
1 Z1 20BK GROUND
2 G9 20GY/BK RED BRAKE WARNING INDICATOR DRIVER
BYPASS JUMPER (A/T) - GREEN 2 WAY
CAV CIRCUIT FUNCTION
1 T141 14YL/RD FUSED IGNITION SWITCH OUTPUT (START)
2 T141 14YL/RD FUSED IGNITION SWITCH OUTPUT (START)
C105 - (FOG LAMP JUMPER SIDE)
CAV CIRCUIT
1 L34 20RD/OR
2 L39 20LB
BR/BE8W-80 CONNECTOR PIN-OUTS 8W - 80 - 7

(4) Connect the 0-414 kPa (0-60 psi) fuel pressure
test gauge (from Gauge Set 5069) to the test port on
the appropriate Adaptor Tool.The DRBtIII Scan
Tool along with the PEP module, the 500 psi
pressure transducer, and the transducer-to-test
port adapter may also be used in place of the
fuel pressure gauge.
The fittings on both tools must be in good
condition and free from any small leaks before
performing the proceeding test.
(5) Start engine and bring to normal operating
temperature.
(6) Observe test gauge. Normal operating pressure
should be 339 kPa +/±34 kPa (49.2 psi +/±5 psi).
(7) Shut engine off.
(8) Pressure should not fall below30 psi for five
minutes.
(9) If pressure falls below 30 psi, it must be deter-
mined if a fuel injector, the check valve within the
fuel pump module, or a fuel tube/line is leaking.
(10) Again, start engine and bring to normal oper-
ating temperature.
(11) Shut engine off.
(12)Testing for fuel injector or fuel rail leak-
age:Clamp off the rubber hose portion of Adaptor
Tool between the fuel rail and the test port ªTº on
Adapter Tool. If pressure now holds at or above 30
psi, a fuel injector or the fuel rail is leaking.
(13)Testing for fuel pump check valve, filter/
regulator check valve or fuel tube/line leakage:
Clamp off the rubber hose portion of Adaptor Tool
between the vehicle fuel line and test port ªTº on
Adapter Tool. If pressure now holds at or above 30
psi, a leak may be found at a fuel tube/line. If no
leaks are found at fuel tubes or lines, one of the
check valves in either the electric fuel pump or filter/
regulator may be leaking.
Note: A quick loss of pressure usually indicates a
defective check valve in the filter/regulator. A slow
loss of pressure usually indicates a defective check
valve in the electric fuel pump.
The electric fuel pump is not serviced separately.
Replace the fuel pump module assembly. The filter/
regulator may be replaced separately on certain
applications. Refer to Fuel Filter/Fuel Pressure Reg-
ulator Removal/Installation for additional informa-
tion.STANDARD PROCEDURE - FUEL SYSTEM
PRESSURE RELEASE
Use following procedure if the fuel injector
rail is, or is not equipped with a fuel pressure
test port.
(1) Remove fuel fill cap.
(2) Remove fuel pump relay from Power Distribu-
tion Center (PDC). For location of relay, refer to label
on underside of PDC cover.
(3) Start and run engine until it stalls.
(4) Attempt restarting engine until it will no
longer run.
(5) Turn ignition key to OFF position.
CAUTION: Steps 1, 2, 3 and 4 must be performed to
relieve high pressure fuel from within fuel rail. Do
not attempt to use following steps to relieve this
pressure as excessive fuel will be forced into a cyl-
inder chamber.
(6) Unplug connector from any fuel injector.
(7) Attach one end of a jumper wire with alligator
clips (18 gauge or smaller) to either injector terminal.
(8) Connect other end of jumper wire to positive
side of battery.
(9) Connect one end of a second jumper wire to
remaining injector terminal.
CAUTION: Powering an injector for more than a few
seconds will permanently damage the injector.
(10) Momentarily touch other end of jumper wire
to negative terminal of battery for no more than a
few seconds.
(11) Place a rag or towel below fuel line quick-con-
nect fitting at fuel rail.
(12) Disconnect quick-connect fitting at fuel rail.
Refer to Quick-Connect Fittings.
(13) Return fuel pump relay to PDC.
(14) One or more Diagnostic Trouble Codes (DTC's)
may have been stored in PCM memory due to fuel
pump relay removal. The DRBtscan tool must be
used to erase a DTC.
BR/BEFUEL DELIVERY - GASOLINE 14 - 3
FUEL DELIVERY - GASOLINE (Continued)

heated air. This air conditioning system uses a fixed ori-
fice tube in the middle of the liquid line to meter refrig-
erant flow to the evaporator coil. To maintain minimum
evaporator temperature and prevent evaporator freez-
ing, the a/c low pressure switch on the accumulator
cycles the compressor clutch.
OPERATION - REFRIGERANT SYSTEM SERVICE
PORT
The high pressure service port is located on the liq-
uid line between the condenser and the evaporator,
near the front of the engine compartment. The low
pressure service port is located on the suction line,
near the accumulator outlet.
Each of the service ports has a threaded plastic
protective cap installed over it from the factory. After
servicing the refrigerant system, always reinstall
both of the service port caps.
DIAGNOSIS AND TESTING - A/C
PERFORMANCE
The air conditioning system is designed to provide
the passenger compartment with low temperature
and low humidity air. The evaporator, located in the
HVAC housing on the dash panel below the instru-
ment panel, is cooled to temperatures near the freez-
ing point. As warm damp air passes through the
cooled evaporator, the air transfers its heat to the
refrigerant in the evaporator tubes and the moisture
in the air condenses on the evaporator fins. During
periods of high heat and humidity, an air condition-
ing system will be more effective in the recirculation
mode (Max-A/C). With the system in the recirculation
mode, only air from the passenger compartment
passes through the evaporator. As the passenger com-
partment air dehumidifies, the air conditioning sys-
tem performance levels improve.
Humidity has an important bearing on the temper-
ature of the air delivered to the interior of the vehi-
cle. It is important to understand the effect that
humidity has on the performance of the air condition-
ing system. When humidity is high, the evaporator
has to perform a double duty. It must lower the air
temperature, and it must lower the temperature of
the moisture in the air that condenses on the evapo-
rator fins. Condensing the moisture in the air trans-
fers heat energy into the evaporator fins and tubing.
This reduces the amount of heat the evaporator can
absorb from the air. High humidity greatly reduces
the ability of the evaporator to lower the temperature
of the air.
However, evaporator capacity used to reduce the
amount of moisture in the air is not wasted. Wring-
ing some of the moisture out of the air entering the
vehicle adds to the comfort of the passengers.
Although, an owner may expect too much from theirair conditioning system on humid days. A perfor-
mance test is the best way to determine whether the
system is performing up to standard. This test also
provides valuable clues as to the possible cause of
trouble with the air conditioning system.
Before proceeding, (Refer to 24 - HEATING & AIR
CONDITIONING/PLUMBING - WARNING) and
(Refer to 24 - HEATING & AIR CONDITIONING/
PLUMBING - CAUTION). The air temperature in
the test room and in the vehicle must be a minimum
of 21É C (70É F) for this test.
(1)
Connect a tachometer and a manifold gauge set.
(2) Set the a/c heater mode control switch knob to
the recirculation mode (Max-A/C) position, the tem-
perature control knob to the full cool position, and
the blower motor switch to the highest speed posi-
tion.
(3) Start the engine and hold the idle speed at
1,000 rpm with the compressor clutch engaged. If the
compressor clutch does not engage, (Refer to 24 -
HEATING & AIR CONDITIONING/CONTROLS/A/C
COMPRESSOR CLUTCH COIL - DIAGNOSIS AND
TESTING).
(4) The engine should be at operating temperature.
The doors and windows must be closed and the hood
must be mostly closed.
(5)
Insert a thermometer in the driver side center
A/C (panel) outlet. Operate the engine for five minutes.
(6) The compressor clutch may cycle, depending
upon the ambient temperature and humidity. If the
clutch cycles, unplug the a/c low pressure switch wire
harness connector from the switch located on the
accumulator (Fig. 2). Place a jumper wire between
the two cavities of the a/c low pressure switch wire
harness connector.
Fig. 2 A/C LOW PRESSURE SWITCH
1 - A/C LOW PRESSURE SWITCH
2 - ACCUMULATOR
24 - 2 HEATING & AIR CONDITIONINGBR/BE
HEATING & AIR CONDITIONING (Continued)

REMOVAL
(1) Disconnect and isolate the battery negative
cable.
(2) Unplug the wire harness connector from the a/c
high pressure switch, which is mounted to a fitting
on the discharge line between the compressor and
the condenser inlet.
(3) Unscrew the a/c high pressure switch from the
discharge line fitting.
(4) Remove the a/c high pressure switch from the
vehicle.
(5) Remove the O-ring seal from the discharge line
fitting and discard.
INSTALLATION
(1) Lubricate a new O-ring seal with clean refrig-
erant oil and install it on the discharge line fitting.
Use only the specified O-rings as they are made of a
special material for the R-134a system. Use only
refrigerant oil of the type recommended for the com-
pressor in the vehicle. (Refer to 24 - HEATING &
AIR CONDITIONING/PLUMBING/REFRIGERANT
OIL - DESCRIPTION)
(2) Install and tighten the high pressure cut-off
switch on the discharge line fitting. The switch
should be hand-tightened onto the discharge line fit-
ting.
(3) Plug the wire harness connector into the high
pressure cut-off switch.
(4) Connect the battery negative cable.
A/C LOW PRESSURE SWITCH
DESCRIPTION
The a/c low pressure switch is located on the top of
the accumulator. The switch is screwed onto an accu-
mulator fitting that contains a Schrader-type valve,
which allows the switch to be serviced without dis-
charging the refrigerant system. The accumulator fit-
ting is equipped with an O-ring to seal the switch
connection.
OPERATION
The a/c low pressure switch is connected in series
electrically with the a/c high pressure switch and the
a/c heater control, between ground and the Power-
train Control Module (PCM). The switch contacts
open and close causing the PCM to turn the compres-
sor clutch on and off. This regulates the refrigerant
system pressure and controls evaporator tempera-
ture. Controlling evaporator temperature prevents
condensate water on the evaporator fins from freez-
ing and obstructing air conditioning system air flow.
The a/c low pressure switch contacts are open
when the suction pressure is about 152-165 kPa(22-24 psi) or lower. The switch contacts will close
when the suction pressure rises to about 255-296 kPa
(37-43 psi) or above. Lower ambient temperatures,
below about -1É C (30É F), will also cause the switch
contacts to open. This is due to the pressure/temper-
ature relationship of the refrigerant in the system.
The a/c low pressure switch is a factory-calibrated
unit. It cannot be adjusted or repaired and, if faulty
or damaged, it must be replaced.
DIAGNOSIS AND TESTING - A/C LOW
PRESSURE SWITCH
Before performing diagnosis of the a/c low pressure
switch, be certain that the switch is properly
installed on the accumulator fitting. If the switch is
too loose it may not open the Schrader-type valve in
the accumulator fitting, which will prevent the
switch from correctly monitoring the refrigerant sys-
tem pressure. Also verify that the refrigerant system
has the correct refrigerant charge. (Refer to 24 -
HEATING & AIR CONDITIONING - DIAGNOSIS
AND TESTING - A/C PERFORMANCE)
Remember that lower ambient temperatures, below
about -1É C (30É F), during cold weather will open the
switch contacts and prevent compressor operation
due to the pressure/temperature relationship of the
refrigerant. For circuit descriptions and diagrams,
(Refer to Appropriate Wiring Information).
(1) Disconnect and isolate the battery negative
cable.
(2) Unplug the a/c low pressure switch wire har-
ness connector from the switch on the accumulator
fitting.
(3) Install a jumper wire between the two cavities
of the a/c low pressure switch wire harness connector.
(4) Connect a manifold gauge set to the refrigerant
system service ports. (Refer to 24 - HEATING & AIR
CONDITIONING/PLUMBING - STANDARD PRO-
CEDURE - REFRIGERANT SYSTEM SERVICE
EQUIPMENT)
(5) Connect the battery negative cable.
(6) Place the a/c heater mode control switch knob
in any A/C position and start the engine.
(7) Check for continuity between the two terminals
of the low pressure cycling clutch switch. There
should be continuity with a suction pressure reading
of 296 kPa (43 psi) or above, and no continuity with a
suction pressure reading of 172 kPa (25 psi) or below.
If OK, test and repair the A/C switch sense circuit as
required. If not OK, replace the faulty switch.
REMOVAL
(1) Disconnect and isolate the battery negative
cable.
BR/BECONTROLS 24 - 21
A/C HIGH PRESSURE SWITCH (Continued)