Content .. 569 570 571 572 ..

Jeep Grand Cherokee WJ. Manual - part 571

switch from correctly monitoring the refrigerant sys-
tem pressure.

Also verify that the refrigerant system has the cor-

rect refrigerant charge. See Refrigerant System
Charge in this group for the procedures.

For circuit descriptions and diagrams, refer to

8W-42 - Air Conditioning/Heater in Group 8W - Wir-
ing Diagrams.

(1) Disconnect and isolate the battery negative

cable.

(2) Unplug the low pressure switch wire harness

connector from the switch on the accumulator fitting.

(3) Install a jumper wire between the two cavities

of the low pressure switch wire harness connector.

(4) Connect a manifold gauge set to the refrigerant

system service ports. See Refrigerant System Service
Equipment in this group for the procedures.

(5) Connect the battery negative cable.
(6) Place the heater-A/C 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 switch. There should be continu-
ity with a suction pressure reading of 262 kPa (38
psi) or above, and no continuity with a suction pres-
sure reading of 141 kPa (20.5 psi) or below. If OK,
test and repair the A/C switch sense circuit as
required. If not OK, replace the faulty switch.

REFRIGERANT SYSTEM LEAKS

WARNING: REVIEW THE WARNINGS AND CAU-
TIONS IN THE FRONT OF THIS GROUP BEFORE
LEAK TESTING THE SYSTEM.

If the air conditioning system is not cooling prop-

erly, determine if the refrigerant system is fully-
charged. See A/C Performance in this group for the
procedures. If the refrigerant system is low or empty;
a leak at a refrigerant line, connector fitting, compo-
nent, or component seal is likely.

An electronic leak detector designed for R-134a

refrigerant is recommended for locating and confirm-
ing refrigerant system leaks. Refer to the operating
instructions supplied by the equipment manufacturer
for proper care and use of this equipment.

An oily residue on or near refrigerant system lines,

connector fittings, components, or component seals
can indicate the general location of a possible refrig-
erant leak. However, the exact leak location should
be confirmed with an electronic leak detector prior to
component repair or replacement.

To detect a leak in the refrigerant system, perform

one of the following procedures:

SYSTEM EMPTY

(1) Evacuate the refrigerant system. See Refriger-

ant System Evacuate in this group for the proce-
dures.

(2) Connect and dispense 0.283 kilograms (0.625

pounds or 10 ounces) of R-134a refrigerant into the
evacuated refrigerant system. See Refrigerant Sys-
tem Charge in this group for the procedures.

(3) Position the vehicle in a wind-free work area.

This will aid in detecting small leaks.

(4) With the engine not running, use a electronic

R-134a leak detector and search for leaks. Because
R-134a refrigerant is heavier than air, the leak detec-
tor probe should be moved slowly along the bottom
side of all refrigerant lines, connector fittings and
components.

(5) To inspect the evaporator coil for leaks, insert

the electronic leak detector probe into the center
instrument panel outlet. Set the blower motor switch
to the lowest speed position, the A/C button in the
On position, and select the Recirculation Mode.

SYSTEM LOW

(1) Position the vehicle in a wind-free work area.

This will aid in detecting small leaks.

(2) Bring the refrigerant system up to operating

temperature and pressure. This is done by allowing
the engine to run with the air conditioning system
turned on for five minutes.

(3) With the engine not running, use a electronic

(4) To inspect the evaporator coil for leaks, insert

VACUUM SYSTEM

Vacuum control is used to operate the mode doors

in the standard equipment manual temperature con-
trol system heater-A/C housing. Testing of the heat-
er-A/C mode control switch operation will determine
if the vacuum, and electrical controls are functioning.
However, it is possible that a vacuum control system
that operates perfectly at engine idle (high engine
vacuum) may not function properly at high engine
speeds or loads (low engine vacuum). This can be
caused by leaks in the vacuum system, or a faulty
vacuum check valve.

A vacuum system test will help to identify the

source of poor vacuum system performance or vac-
uum system leaks. Before starting this test, stop the

24 - 26

HEATING AND AIR CONDITIONING

DIAGNOSIS AND TESTING (Continued)

engine and make certain that the problem isn’t a dis-
connected vacuum supply tube at the engine intake
manifold vacuum tap or the vacuum reservoir.

Use an adjustable vacuum test set (Special Tool

C-3707-B) and a suitable vacuum pump to test the
heater-A/C vacuum control system. With a finger
placed over the end of the vacuum test hose probe
(Fig. 10), adjust the bleed valve on the test set gauge
to obtain a vacuum of exactly 27 kPa (8 in. Hg.).
Release and block the end of the probe several times
to verify that the vacuum reading returns to the
exact 27 kPa (8 in. Hg.) setting. Otherwise, a false
reading will be obtained during testing.

VACUUM CHECK VALVES

(1) Remove the vacuum check valve to be tested.

The valves are located in the (black) vacuum supply
tubes at either the engine intake manifold vacuum
tap, or on the bottom of the HVAC unit behind the
passenger front floor duct.

(2) Connect the test set vacuum supply hose to the

heater-A/C control side of the valve. When connected
to this side of the check valve, no vacuum should
pass and the test set gauge should return to the 27
kPa (8 in. Hg.) setting. If OK, go to step Step 3. If
not OK, replace the faulty valve.

(3) Connect the test set vacuum supply hose to the

engine vacuum side of the valve. When connected to
this side of the check valve, vacuum should flow
through the valve without restriction. If not OK,
replace the faulty valve.

HEATER-A/C CONTROLS

(1) Connect the test set vacuum probe to the heat-

er-A/C vacuum supply (black) tube in the engine
compartment. Position the test set gauge so that it
can be viewed from the passenger compartment.

(2) Place the heater-A/C mode control switch knob

in each mode position, one position at a time, and
pause after each selection. The test set gauge should
return to the 27 kPa (8 in. Hg.) setting shortly after
each selection is made. If not OK, a component or
vacuum line in the vacuum circuit of the selected
mode has a leak. See the procedure in Locating Vac-
uum Leaks.

CAUTION: Do not use lubricant on the switch ports
or in the holes in the plug, as lubricant will ruin the
vacuum valve in the switch. A drop of clean water
in the connector plug holes will help the connector
slide onto the switch ports.

LOCATING VACUUM LEAKS

WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS,

REFER

GROUP

PASSIVE

RESTRAINT SYSTEMS BEFORE ATTEMPTING ANY
STEERING

WHEEL,

STEERING

COLUMN,

INSTRUMENT PANEL COMPONENT DIAGNOSIS OR
SERVICE. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.

(1) Disconnect the vacuum harness connector from

the back of the heater-A/C mode control switch on
the control panel.

(2) Connect the test set vacuum hose probe to each

port in the vacuum harness connector, one at a time,
and pause after each connection (Fig. 11). The test
set gauge should return to the 27 kPa (8 in. Hg.) set-
ting shortly after each connection is made. If OK,
replace the faulty mode control switch. If not OK, go
to Step 3.

(3) Determine the vacuum line color of the vacuum

circuit that is leaking. To determine the vacuum line
colors, refer to the Vacuum Circuits chart (Fig. 12).

(4) Disconnect and plug the vacuum line from the

component (fitting, actuator, valve, switch, or reser-
voir) on the other end of the leaking circuit. Instru-
ment panel disassembly or removal may be necessary
to gain access to some components.

(5) Connect the test set hose or probe to the open

end of the leaking circuit. The test set gauge should
return to the 27 kPa (8 in. Hg.) setting shortly after
each connection is made. If OK, replace the faulty
disconnected component. If not OK, go to Step 6.

Fig. 10 Adjust Vacuum Test Bleed Valve-Typical

1 – VACUUM PUMP TOOL C-4289
2 – VACUUM TEST SET C-3707
3 – BLEED VALVE
4 – PROBE

HEATING AND AIR CONDITIONING

24 - 27

DIAGNOSIS AND TESTING (Continued)

(6) To locate a leak in a vacuum line, leave one

end of the line plugged and connect the test set hose
or probe to the other end. Run your fingers slowly
along the line while watching the test set gauge. The
vacuum reading will fluctuate when your fingers con-
tact the source of the leak. To repair the vacuum
line, cut out the leaking section of the line. Then,

insert the loose ends of the line into a suitable length
of 3 millimeter (1/8-inch) inside diameter rubber
hose.

SERVICE PROCEDURES

REFRIGERANT OIL LEVEL

When an air conditioning system is assembled at

the factory, all components except the compressor are
refrigerant oil free. After the refrigerant system has
been charged and operated, the refrigerant oil in the
compressor is dispersed throughout the refrigerant
system. The accumulator, evaporator, condenser, and
compressor will each retain a significant amount of
the needed refrigerant oil.

It is important to have the correct amount of oil in

the refrigerant system. This ensures proper lubrica-
tion of the compressor. Too little oil will result in
damage to the compressor. Too much oil will reduce
the cooling capacity of the air conditioning system.

It will not be necessary to check the oil level in the

compressor or to add oil, unless there has been an oil
loss. An oil loss may occur due to a rupture or leak
from a refrigerant line, a connector fitting, a compo-
nent, or a component seal. If a leak occurs, add 30
milliliters (1 fluid ounce) of refrigerant oil to the
refrigerant system after the repair has been made.
Refrigerant oil loss will be evident at the leak point
by the presence of a wet, shiny surface around the
leak.

Refrigerant oil must be added when a accumulator,

evaporator coil, or condenser are replaced. See the
Refrigerant Oil Capacities chart. When a compressor
is replaced, the refrigerant oil must be drained from
the old compressor and measured. Drain all of the
refrigerant oil from the new compressor, then fill the
new compressor with the same amount of refrigerant
oil that was drained out of the old compressor.

Fig. 11 Vacuum Circuit Test

Fig. 12 Vacuum Circuits

Refrigerant Oil Capacities

Component

fl oz

A/C System

170

5.75

Accumulator

110.6

3.75

Condenser

6.5

0.22

Evaporator

62.7

2.12

Compressor

drain and measure the oil
from the old compressor
- see text.

24 - 28

HEATING AND AIR CONDITIONING

DIAGNOSIS AND TESTING (Continued)

2000 WJ Service Manual
Publication No. 81-370-0047
TSB 26-12-00

December, 2000

REFRIGERANT RECOVERY

WARNING: REVIEW THE WARNINGS AND CAU-
TIONS IN THE GENERAL INFORMATION SECTION
NEAR THE FRONT OF THIS GROUP BEFORE
RECOVERING REFRIGERANT.

A R-134a refrigerant recovery/recycling/charging

station that meets SAE Standard J2210 must be
used to recover the refrigerant from an R-134a refrig-
erant system. Refer to the operating instructions sup-
plied by the equipment manufacturer for the proper
care and use of this equipment.

REFRIGERANT SYSTEM CHARGE

WARNING: REVIEW THE WARNINGS AND CAU-
TIONS IN THE FRONT OF THIS GROUP BEFORE
CHARGING THE REFRIGERANT SYSTEM.

After the refrigerant system has been tested for

leaks and evacuated, a refrigerant charge can be
injected into the system. See Refrigerant Charge
Capacity for the proper amount of the refrigerant
charge.

A R-134a refrigerant recovery/recycling/charging

station that meets SAE Standard J2210 must be
used to charge the refrigerant system with R-134a
refrigerant. Refer to the operating instructions sup-
plied by the equipment manufacturer for proper care
and use of this equipment.

REFRIGERANT CHARGE CAPACITY

The R-134a refrigerant system charge capacity for

this vehicle is 0.680 kilograms (1.50 pounds/24 ounc-
es).

PARTIAL CHARGE METHOD

WARNING: REVIEW THE WARNINGS AND CAU-
TIONS IN THE FRONT OF THIS GROUP BEFORE
CHARGING THE REFRIGERANT SYSTEM.

The partial charge method is used to add a partial

charge to a refrigerant system that is low on refrig-
erant. To perform this procedure the evaporator inlet
and outlet tube temperatures are measured. The
temperature difference is measured with a tempera-
ture meter with one or two clamp-on thermocouple
probes. The difference between the evaporator inlet
and outlet tube temperatures will determine the
amount of refrigerant needed.

Before adding a partial refrigerant charge, check

for refrigerant system leaks. See Refrigerant System
Leaks in this group for the procedures. If a leak is
found, make the necessary repairs before attempting
a full or partial refrigerant charge.

(1) Attach a manifold gauge set to the refrigerant

system service ports.

(2) Attach the two clamp-on thermocouple probes

to the inlet and outlet tubes of the evaporator coil.

a. If a single thermocouple probe is used, attach

the probe to the evaporator inlet tube just before the
collar of the refrigerant line connector fitting. The
probe must make contact with the bottom surface of
the evaporator inlet tube.

b. If dual thermocouple probes are used, attach

probe 1 to the evaporator inlet tube, and probe 2 to
the evaporator outlet tube. Attach both probes to the
evaporator tubes just before the collar of the refrig-
erant line connector fittings. The probes must make
contact with the bottom surfaces of the evaporator
inlet and outlet tubes.

(3) Open all of the windows or doors of the passen-

ger compartment.

(4) Set the A/C button on the heater-A/C controls

to the on position, the temperature control knob in
the full cool position, select the Recirculation Mode,
and place the blower motor switch in the highest
speed position.

(5) Start the engine and hold the engine idle speed

at 1,000 rpm. Allow the engine to warm up to normal
operating temperature.

(6) The compressor clutch may cycle, depending

upon ambient temperature, humidity, and the refrig-
erant system charge level. If the compressor clutch
cycles, unplug the wire harness connector from the
low pressure cycling clutch switch on the accumula-
tor. Install a jumper wire between the two cavities of
the switch wire harness connector.

(7) Hold the engine idle speed at 1,000 rpm.
(8) Allow three to five minutes for the refrigerant

system to stabilize, then record the temperatures of
the evaporator inlet and outlet tubes.

a. If a single probe is used, record the temperature

of the evaporator inlet tube. Then remove the probe
from the inlet tube and attach it to the evaporator
outlet tube just before the collar of the refrigerant
line connector fitting. The probe must make contact
with the bottom surface of the evaporator outlet tube.
Allow the thermocouple and meter time to stabilize,
then record the temperature of the evaporator outlet
tube. Subtract the inlet tube temperature reading
from the outlet tube temperature reading.

b. If dual probes are used, record the temperatures

of both the evaporator inlet and outlet tubes. Then
subtract the inlet tube temperature reading from the
outlet tube temperature reading.

(9) If the measured temperature differential is

higher than 22° C to 26° C (40° F to 47° F), add 0.4
kilograms (14 ounces) of refrigerant.

(10) Allow three to five minutes for the refrigerant

system to stabilize, then take a second set of thermo-

HEATING AND AIR CONDITIONING

24 - 29

SERVICE PROCEDURES (Continued)

Content .. 569 570 571 572 ..