2003 JEEP GRAND CHEROKEE hvac

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 their
air 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.
If the vehicle has the optional Automatic Zone Control
(AZC) system, and has intermittent operational prob-
lems or fault codes, be certain that the wire harness
connectors on the HVAC housing are properly seated
(Fig. 2). To check this condition, unplug the two wire
harness connector halves, then plug them in again.
Before performing the following procedure, (Refer
to 24 - HEATING & AIR CONDITIONING/PLUMB-
ING - CAUTION) (Refer to 24 - HEATING & AIR
CONDITIONING/PLUMBING - WARNING). 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) If the vehicle has the standard manual temper-
ature control, set the A/C Heater mode control switch
knob in the Panel position, the temperature control
knob in the full cool (Fresh Air Mode) position, the
A/C button in the On position, and the blower motor
switch knob in the highest speed position. If the vehi-
cle has the optional AZC, set the A/C Heater mode
control switch knob in the Panel position, the tem-
perature control knob in the full cool position, the
A/C button in the On position, and the blower motor
switch knob in the highest (manual) speed position.
(3) Start the engine and hold the idle at 1,300 rpm
with the compressor clutch engaged.
(4) The engine should be at operating temperature.
The doors and windows must be open.
(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.(7) With the compressor clutch engaged, record the
discharge air temperature and the compressor dis-
charge pressure.
(8) Compare the discharge air temperature to the
Performance Temperature and Pressure chart. If the
discharge air temperature is high, (Refer to 24 -
HEATING & AIR CONDITIONING/PLUMBING -
DIAGNOSIS AND TESTING - REFRIGERANT SYS-
TEM LEAKS) and (Refer to 24 - HEATING & AIR
CONDITIONING/PLUMBING - STANDARD PRO-
CEDURE - REFRIGERANT SYSTEM CHARGE).
Performance Temperature and Pressure
Ambient Air Temperature
and Humidity21É C
(70É F @ 80%
humidity)27É C
(80É F @ 80%
humidity)32É C
(90É F @ 80%
humidity)38É C
(100ÉF@50%
humidity)43É C
110É F @ 20%
humidity)
Air Temperature at Center
Panel Outlet10 to 13É C
(50 to 55É F)14 to 17É C
(58 to 63É F)15 to 18É C
(60 to 65É F)17 to 20É C
(63 to 68É F)14 to 17É C
(58 to 63É F)
Evaporator Inlet Pressure
at Charge Port241 to 276 kPa
(35 to 40 psi)262 to 290 kPa
(38 to 42 psi)269 to 296 kPa
(39 to 43 psi)275 to 303 kPa
(40 to 44 psi)262 to 290 kPa
(38 to 42 psi)
Compressor Discharge
Pressure1241 to 1792
kPa
(180 to 260 psi)1380 to 1930
kPa
(200 to 280 psi)1380 to 1930
kPa
(200 to 280 psi)1655 to 2206
kPa
(240 to 320 psi)1567 to 2068
kPa
(220 to 300 psi)
Note: The discharge air temperatures will be lower if the humidity is less than the percentages shown.
Fig. 2 HVAC Housing - (rear view)
1 - Instrument Panel
2 - Air Intake
3 - Expansion Valve
4 - HVAC Housing
5 - Heater Core Input/Output Ports
6 - Instrument Panel Wiring Harness
7 - Blower Motor
WJHEATING & AIR CONDITIONING 24 - 3
HEATING & AIR CONDITIONING (Continued)

DIAGNOSIS AND TESTING - HEATER
PERFORMANCE
Before performing the following tests, refer to Cool-
ing for the procedures to check the radiator coolant
level, serpentine drive belt tension, radiator air flow
and the radiator fan operation. Also be certain that
the accessory vacuum supply line is connected at the
engine intake manifold for the manual temperature
control system.
MAXIMUM HEATER OUTPUT
Engine coolant is delivered to the heater core
through two heater hoses. With the engine idling at
normal operating temperature, set the temperature
control knob in the full hot position, the mode control
switch knob in the floor heat position, and the blower
motor switch knob in the highest speed position.
Using a test thermometer, check the temperature of
the air being discharged at the HVAC housing floor
outlets. Compare the test thermometer reading to the
Temperature Reference chart.
Temperature Reference
Ambient Air Temperature15.5É C
(60É F)21.1É C
(70É F)26.6É C
(80É F)32.2É C
(90É F)
Minimum Air Temperature at
Floor Outlet62.2É C
(144É F)63.8É C
(147É F)65.5É C
(150É F)67.2É C
(153É F)
If the floor outlet air temperature is too low, refer
to Cooling to check the engine coolant temperature
specifications. Both of the heater hoses should be hot
to the touch. The coolant return heater hose should
be slightly cooler than the coolant supply heater
hose. If the return hose is much cooler than the sup-
ply hose, locate and repair the engine coolant flow
obstruction in the cooling system. Refer to Cooling
for the procedures.
OBSTRUCTED COOLANT FLOW
Possible locations or causes of obstructed coolant
flow:
²Pinched or kinked heater hoses.
²Improper heater hose routing.
²Plugged heater hoses or supply and return ports
at the cooling system connections.
²A plugged heater core.
If proper coolant flow through the cooling system is
verified, and heater outlet air temperature is still
low, a mechanical problem may exist.
MECHANICAL PROBLEMS
Possible locations or causes of insufficient heat:
²An obstructed cowl air intake.
²Obstructed heater system outlets.
²A blend door not functioning properly.
TEMPERATURE CONTROL
If the heater outlet air temperature cannot be
adjusted with the temperature control knob(s) on the
A/C Heater control panel, the following could require
service:
²The A/C heater control.
²The blend door actuator(s).
²The wire harness circuits for the A/C heater con-
trol or the blend door actuator(s).²The blend door(s).
²Improper engine coolant temperature.
STANDARD PROCEDURE - DIODE
REPLACEMENT
(1) Disconnect and isolate the negative battery
cable.
(2) Locate the diode in the harness, and remove
the protective covering.
(3) Remove the diode from the harness, pay atten-
tion to the current flow direction (Fig. 3).
(4) Remove the insulation from the wires in the
harness. Only remove enough insulation to solder in
the new diode.
Fig. 3 DIODE IDENTIFICATION
1 - CURRENT FLOW
2 - BAND AROUND DIODE INDICATES CURRENT FLOW
3 - DIODE AS SHOWN IN THE DIAGRAMS
24 - 6 HEATING & AIR CONDITIONINGWJ
HEATING & AIR CONDITIONING (Continued)

TORQUE SPECIFICATIONS
TORQUE SPECIFICATIONS
DESCRIPTION N´m Ft. Lbs. In. Lbs.
A/C COMPRESSOR
SHAFT BOLT13 9.6 115
A/C COMPRESOR LINE
MANIFOLD FASTENERS
4.0L/4.7L25.4 18.75 225
A/C COMPRESOR LINE
MANIFOLD FASTENERS
2.7L DIESEL22 16.2 195
A/C COMPRESSOR TO
ENGINE BLOCK BOLTS -
4.0L/4.7L45-65 33-48 398-575
A/C COMPRESSOR TO
ENGINE BLOCK BOLTS -
2.7L DIESEL30 22 266
A/C COMPRESSOR REAR
BRACE BOLTS - 4.0L40-55 30-41 354-487
A/C COMPRESSOR REAR
BRACE BOLTS - 4.7L35-45 26-33 310-398
A/C CONDENSER TO
REFRIG. LINE
FASTENERS28 21 248
A/C EVAPORATOR LINE to
TXV FASTENERS28 21 247
ACCUMULATOR
RETAINING BAND
(4.0L/4.7L)12 9.0 106
ACCUMULATOR
RETAINING BAND (3.1L
DIESEL)5 3.7 44
BLOWER MOTOR
SCREWS2.2 1.7 20
DOOR ACTUATOR
SCREWS2.2 1.7 20
HVAC HOUSING SCREWS 2.2 1.7 20
HVAC HOUSING TO DASH
PANEL NUTS (ENGINE
COMP. SIDE)75 62
HVAC HOUSING TO DASH
PANEL NUTS
(PASSENGER COMP.
SIDE)4.5 3.3 40
EXPANSION VALVE TO
HVAC FASTENERS20 15 177
SUCTION LINE TO
ACCUMULATOR FITTING28 20.7 248
24 - 8 HEATING & AIR CONDITIONINGWJ
HEATING & AIR CONDITIONING (Continued)

VACUUM RESERVOIR
DESCRIPTION.........................34
OPERATION...........................34
REMOVAL.............................35
INSTALLATION.........................35EVAPORATOR TEMPERATURE SENSOR
DESCRIPTION.........................35
OPERATION...........................35
REMOVAL.............................35
INSTALLATION.........................35
CONTROLS
DIAGNOSIS AND TESTING - VACUUM SYSTEM
Vacuum control is used to operate the mode doors
in the standard equipment manual temperature con-
trol system HVAC housing. Testing of the A/C Heater
mode control switch operation will determine if the
vacuum and electrical controls are functioning. How-
ever, it is possible that a vacuum control system that
operates perfectly at engine idle (high engine vac-
uum) 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
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
HVAC vacuum control system. With a finger placed
over the end of the vacuum test hose probe (Fig. 1),
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
A/C Heater 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 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.
A/C HEATER CONTROL
(1) Connect the test set vacuum probe to the
HVAC vacuum supply (black) tube in the engine com-
partment. Position the test set gauge so that it can
be viewed from the passenger compartment.
(2) Place the A/C Heater 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.
Fig. 1 ADJUST VACUUM TEST BLEED VALVE -
TYPICAL
1 - VACUUM PUMP TOOL C-4289
2 - VACUUM TEST SET C-3707
3 - BLEED VALVE
4 - PROBE
24 - 10 CONTROLSWJ

open circuit to the fuse in the junction block as
required.
(5) The coil ground terminal cavity (85) is switched
to ground through the Powertrain Control Module
(PCM). There should be continuity between this cav-
ity and the A/C compressor clutch relay control cir-
cuit cavity of the PCM wire harness connector C
(gray) at all times. If not OK, repair the open circuit
as required.
REMOVAL
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the cover from the Power Distribution
Center (PDC) (Fig. 11).
(3) Refer to the label on the PDC for compressor
clutch relay identification and location.
(4) Unplug the compressor clutch relay from the
PDC.
INSTALLATION
(1) Install the compressor clutch relay by aligning
the relay terminals with the cavities in the PDC and
pushing the relay firmly into place.
(2) Install the PDC cover.
(3) Connect the battery negative cable.
(4) Test the relay operation.
A/C HEATER CONTROL
DESCRIPTION
The manual temperature control HVAC system
uses a combination of electrical, and vacuum con-trols. The Automatic Zone Control (AZC) HVAC sys-
tem uses only electrical controls. These controls
provide the vehicle operator with a number of setting
options to help control the climate and comfort
within the vehicle. Refer to the owner's manual in
the vehicle glove box for more information on the
suggested operation and use of these controls.
Both a/c heater control panels are located on the
instrument panel inboard of the steering column and
below the radio (Fig. 12). Both control panels contain
rotary-type temperature control knob(s), a rotary-
type mode control switch knob, a rotary-type blower
motor speed switch knob and an air conditioning
compressor push button switch. The rear window
defogger push button switch is also located on a/c
heater control panel. The AZC control panel also fea-
tures a recirculation push button switch and a vac-
uum fluorescent display area.
OPERATION
The AZC control module uses infrared sensing
technology to control occupant comfort levels, not the
actual passenger compartment air temperature. Dual
infrared sensors mounted in the face of the control
unit independently measure the surface temperature
to maintain customer-perceived comfort temperature
under changing conditions. Dual Zone temperature
control provides wide side-to-side variation in comfort
temperature to exceed the needs of either front seat
occupant. This sensing system replaces interior air
temperature and solar sensors used to approximate
direct sensing control through complex control pro-
grams.
Fig. 11 POWER DISTRIBUTION CENTER (PDC)
1 - TRANSMISSION CONTROL MODULE (TCM)
2 - NEGATIVE CABLE
3 - POSITIVE CABLE
4 - POWER DISTRIBUTION CENTER (PDC)
Fig. 12 A/C HEATER CONTROL PANELS
WJCONTROLS 24 - 17
A/C COMPRESSOR CLUTCH RELAY (Continued)

(2)If there are no fault codes, the ª00º dis-
play value will remain in the VF window.Should
there be any codes, each will be displayed for one
second in ascending numerical sequence (note: no
effort is made to display faults in the order they
occurred). The left side set temperature display will
be blanked and the right side set temperature dis-
play will indicate current and historical codes (8 his-
torical max) presently active. Once all codes have
been displayed, the system will repeat the fault code
numbers. This will continue until the left side set
temperature control is moved at least one detent
position in either direction, by pressing both the A/C
and Recirc buttons at the same time, or the ignition
is turned off. Record all of the fault codes, then see
the Current and Historical Fault Code charts for the
descriptions.
CLEARING FAULT CODES
Current faults cannot be electronically cleared.
Repair must be made to the system to eliminate the
fault causing code. Historical fault codes can be
cleared manually, or automatically. To clear a histor-
ical fault manually, depress and hold either the A/C
or Recirc button for at least three seconds while the
display is in the fault code mode of operation. Histor-
ical fault codes are cleared automatically when the
corresponding current fault code has been cleared,
and has remained cleared for a number of ignition
cycles. The faults have been cleared when two hori-
zontal bars appear in the Test Selector display.
EXITING SELF-DIAGNOSTIC MODE
The self-diagnostic mode can be exited by pressing
both the A/C and Recirc buttons at the same time, or
turning off the ignition.
MONITOR CURRENT PARAMETERS
While in the display fault code mode of operation,
current system parameters can also be monitored
and/or forced. Rotating the left side set temperature
control clockwise will increase the pointer number
while rotating the control counter clockwise will
decrease the pointer number. Rotating the right set
temperature control will have no impact on pointer
value or the value of the parameter being monitored.
Once the desired pointer number has been selected,
pressing either the AC or Recirc buttons will display
the current value of the selected parameter.The
right side set temperature display is only capa-
ble of displaying only values ranging from 0 to
99, the left side set temperature display is used
for values greater than 99. If the value is less
than 99, the left side set temperature display
remains blanked.While a parameter is being over-
ridden, the system will continue to function normallyexcept for the parameter which is being manually
controlled.
For values < 0, the9G9segment in the left side set
temperature Most Significant Digit (MSD)(or left-
most number in the pair) will be used to indicate a
negative number. For values between -01 to -99 the
Least Significant Digit (LSD)(or right-most number
of the pair) in the left side set temperature will
remain blank. System control of parameter being dis-
played can be overridden by rotating the right set
temperature control in either direction. Rotating the
right temperature control in the CW direction, the
selected parameter value is overridden and incre-
mented beginning at the value which was being dis-
played. Rotating the right temperature control in the
CCW direction, the selected parameter value is over-
ridden and decremented beginning at the value
which was being displayed. The rate at which incre-
menting and decrement occurs is one unit value per
set temperature detent position.
HVAC SYSTEM POINTER
Pointer
NumberDESCRIPTION Value
Displayed
01 A/C Enable 0 or 1
0=
disabled
1=
enabled
02 Final fan PWM duty cycle 0 to 255
While the value of this pointer
is being displayed, turning the
right set temperature control
either direction will manually
control the value. CW =
increase; CCW = decrease
03 Left NPRG * 0 to 255
* NPRG equals a calculated number based on outside
and in-vehicle conditions. This value is used by the
AZC to position the Mode motor, Air Inlet motor, and
control blower motor speed.
While the value of this pointer
is being displayed, turning the
right set temperature control
either direction will manually
control the value. CW =
increase; CCW = decrease
04 Right NPRG 0 to 255
WJCONTROLS 24 - 21
A/C HEATER CONTROL (Continued)

HVAC SYSTEM POINTER
While the value of this pointer
is being displayed, turning the
right set temperature control
either direction will manually
control the value. CW =
increase; CCW = decrease
05 Avg NPRG 0 TO
255
While the value of this pointer
is being displayed, turning the
right set temperature control
either direction will manually
control the value. CW =
increase; CCW = decrease
06 Primary control side 0 or 1
0 = left 1
= right
07 EE Check sum (calculated) 0 to 255
08 Target intensity (in % ON time) 0 to 255
While the value of this pointer
is being displayed, turning the
right set temperature control
either direction will manually
control the value. CW =
increase; CCW = decrease
09 Not Used 0 to 0
10 Not Used 0 to 0
11 Right NINC * 0 to 255
* NINC equals a calculated number based on the IR
sensor and IR thermistor values used to calculate the
NPRG.
While the value of this pointer
is being displayed, turning the
right set temperature control
either direction will manually
control the value. CW =
increase; CCW = decrease
12 Left NINC 0 to 255
While the value of this pointer
is being displayed, turning the
right set temperature control
either direction will manually
control the value. CW =
increase; CCW = decrease
13 Right NMIX * 0 to 255
* NMIX equals a calculated number based on outside
and in-vehicle conditions used by the AZC to position
the Temperature motors.HVAC SYSTEM POINTER
While the value of this pointer
is being displayed, turning the
right set temperature control
either direction will manually
control the value. CW =
increase; CCW = decrease
14 Left NMIX 0 to 255
While the value of this pointer
is being displayed, turning the
right set temperature control
either direction will manually
control the value. CW =
increase; CW = decrease
15 Not Used 0 to 0
16 Not Used 0 to 0
17 Reserved
18 Reserved
19 Reserved
MODE VALUE POINTER
Pointer
NumberDESCRIPTION Value
Displayed
20 mode range in delta counts 0 to
9999
21 Current mode position (in
counts)0to
9999
22 mode target position in ratio 0 to 255
While the value of this pointer
is being displayed, turning the
right set temperature control
either direction will manually
control the value. CW =
increase; CCW = decrease
23 mode target position in counts 0 to
9999
24 Not Used 0 to 0
25 number of valve moves since
last index0to
9999
26 Not Used 0 to 0
27 Not Used 0 to 0
28 Not Used 0 to 0
29 mode motor state 0 to 5
0 = in position, 1 = moving
toward panel, 2 = moving
toward defrost, 3 = searching
range, 4 = stalled moving
toward panel, 5 = stalled
moving toward defrost
24 - 22 CONTROLSWJ
A/C HEATER CONTROL (Continued)

DIAGNOSIS AND TESTING - A/C PRESSURE
TRANSDUCER
The A/C pressure transducer is tested using a
DRBIIItscan tool. Refer to the appropriate diagnos-
tic information. Before testing the A/C pressure
transducer, be certain that the transducer wire har-
ness connection is clean of corrosion and properly
connected. For the air conditioning system to operate,
an A/C pressure transducer voltage reading between0.7 and 4.56 volts is required. Voltage outside this
range indicate a low or high refrigerant system pres-
sure condition to the Powertrain Control Module
(PCM). The PCM is programmed to respond to a low
or high refrigerant system pressure by suppressing
operation of the compressor. Refer to the A/C Pres-
sure Transducer Voltage table for the possible condi-
tion indicated by the transducer voltage readings.
A/C PRESSURE TRANSDUCER VOLTAGE
VOLTAGE POSSIBLE INDICATION
0.0 1. NO SENSOR SUPPLY VOLTAGE FROM PCM.
2. SHORTED SENSOR CIRCUIT.
3. FAULTY TRANSDUCER
0.150 TO 0.450 1. AMBIENT TEMPERATURE BELOW 10É c (50É F).
2. LOW REFRIGERANT SYSTEM PRESSURE.
0.451 TO 4.519 1. NORMAL REFRIGERANT SYSTEM PRESSURE.
4.520 TO 4.850 1. HIGH REFRIGERANT SYSTEM PRESSURE.
5.0 1. OPEN SENSOR CIRCUIT.
2. FAULTY TRANSDUCER.
REMOVAL
WARNING: Transducer can be removed without
recoverying the system, but some loss of refriger-
ant can be expected(Refer to 24 - HEATING & AIR
CONDITIONING/PLUMBING - WARNING) and (Refer
to 24 - HEATING & AIR CONDITIONING/PLUMBING -
CAUTION).
(1) Disconnect and isolate the battery negative
cable.
(2) Disconnect the headlamp and dash wire har-
ness connector for the A/C pressure transducer from
the transducer connector receptacle.
(3) Using an open end wrench, unscrew the A/C
pressure transducer from the fitting on the discharge
line.
(4) Remove the seal from the A/C pressure trans-
ducer fitting and discard.
INSTALLATION
(1) Lubricate a new O-ring seal with clean refrig-
erant oil and install it on the A/C pressure trans-
ducer fitting.
(2) Using an open end wrench, install and tighten
the A/C pressure transducer onto the fitting on the
discharge line.
(3) Reconnect the headlamp and dash wire harness
connector for the A/C pressure transducer to the
transducer connector receptacle.(4) Reconnect the battery negative cable.
BLOWER MOTOR
CONTROLLER
DESCRIPTION
Models equipped with the optional Automatic Zone
Control (AZC) system have a blower motor controller.
The controller allows the selection of almost infi-
nitely variable blower motor speeds. The controller is
mounted to the HVAC housing, under the instrument
panel and just inboard of the blower motor, in the
same location used for the blower motor resistor on
manual temperature control systems. It can be
accessed without removing any other components.
OPERATION
The blower motor controller output to the blower
motor can be adjusted by the blower motor speed
switch knob on the AZC A/C Heater control panel, or
it can be adjusted automatically by the logic circuitry
and programming of the AZC control module. In
either case, the AZC control module sends the correct
pulse width modulated signal to the blower motor
controller to obtain the selected or programmed
blower motor speed.
The blower motor controller cannot be repaired
and, if faulty or damaged, it must be replaced.
24 - 26 CONTROLSWJ
A/C PRESSURE TRANSDUCER (Continued)