Dodge Durango (DN). Manual — part 189

A/C Diagnosis

CONDITION

POSSIBLE CAUSE

CORRECTION

LOW SIDE PRESSURE
IS NORMAL OR
SLIGHTLY LOW, AND
HIGH SIDE PRESSURE
IS TOO LOW.

1. Low refrigerant system
charge.
2. Refrigerant flow
through the evaporator
coil is restricted.
3. Faulty compressor.

1. See Refrigerant System Leaks in the Diagnosis and
Testing section of this group. Test the refrigerant system
for leaks. Repair, evacuate and charge the refrigerant
system, if required.
2. See Evaporator Coil in the Removal and Installation
section of this group. Replace the restricted evaporator
coil, if required.
3. See Compressor in the Diagnosis and Testing section
of this group. Replace the compressor, if required.

LOW SIDE PRESSURE
IS NORMAL OR
SLIGHTLY HIGH, AND
HIGH SIDE PRESSURE
IS TOO HIGH.

1. Condenser air flow
restricted.
2. Inoperative cooling
fan.
3. Faulty expansion
valve.
4. Refrigerant system
overcharged.
5. Air in the refrigerant
system.
6. Engine overheating.

1. Check the condenser for damaged fins, foreign objects
obstructing air flow through the condenser fins, and
missing or improperly installed air seals. Refer to Group 7
- Cooling System for more information on air seals.
Clean, repair, or replace components as required.
2. Refer to Group 7 - Cooling System for more
information. Test the cooling fan and replace, if required.
3. See Expansion Valve in the Diagnosis and Testing
section of this group. Replace the faulty expansion valve,
if required.
4. See Refrigerant System Charge in the Service
Procedures section of this group. Recover the refrigerant
from the refrigerant system. Charge the refrigerant
system to the proper level, if required.
5. See Refrigerant System Leaks in the Diagnosis and
Testing section of this group. Test the refrigerant system
for leaks. Repair, evacuate and charge the refrigerant
system, if required.
6. Refer to Group 7 - Cooling System for more
information. Test the cooling system and repair, if
required.

LOW SIDE PRESSURE
IS TOO HIGH, AND
HIGH SIDE PRESSURE
IS TOO LOW.

1. Accessory drive belt
slipping.
2. Faulty compressor.

1. Refer to Group 7 - Cooling System for more
information. Inspect the accessory drive belt condition
and tension. Tighten or replace the accessory drive belt, if
required.
2. See Compressor in the Diagnosis and Testing section
of this group. Replace the compressor, if required.

LOW SIDE PRESSURE
IS TOO LOW, AND HIGH
SIDE PRESSURE IS
TOO HIGH.

1. Restricted refrigerant
flow through the
refrigerant lines.
2. Restricted refrigerant
flow through the
expansion valve.
3. Restricted refrigerant
flow through the
condenser.
4. Restricted refrigerant
flow through the
filter-drier.

1. See Liquid Line and Suction and Discharge Line in the
Removal and Installation section of this group. Inspect the
refrigerant lines for kinks, tight bends or improper routing.
Correct the routing or replace the refrigerant line, if
required.
2. See Expansion Valve in the Diagnosis and Testing
section of this group. Replace the restricted expansion
valve, if required.
3. See Condenser in the Removal and Installation section
of this group. Replace the restricted condenser, if
required.
4. See Filter-Drier in the Removal and Installation section
of this group. Replace the restricted filter-drier, if required.

24 - 14

HEATING AND AIR CONDITIONING

DN

DIAGNOSIS AND TESTING (Continued)

BLOWER MOTOR

WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, REFER TO PASSIVE RESTRAINT SYSTEMS
BEFORE ATTEMPTING ANY STEERING WHEEL,
STEERING

COLUMN,

OR

INSTRUMENT

PANEL

COMPONENT DIAGNOSIS OR SERVICE. FAILURE
TO TAKE THE PROPER PRECAUTIONS COULD
RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT
AND POSSIBLE PERSONAL INJURY.

For circuit descriptions and diagrams, refer to Air

Conditioning/Heater in Group 8W - Wiring Diagrams.
Possible causes of an inoperative front or rear blower
motor include:

• Faulty fuse (the rear blower motor fuse is

located in the relay and fuse block located on the
back of the junction block)

• Faulty blower motor circuit wiring or wire har-

ness connectors

• Faulty blower motor resistor

• Faulty blower motor relay (Voltage Reduction

Relay or VRR) (front only)

• Faulty blower motor switch

• Faulty heater-A/C mode control switch (front

only)

• Faulty high speed blower motor relay (front

only)

• Faulty blower motor.
Possible causes of the front or rear blower motor

not operating in all speeds include:

• Faulty fuse (the rear blower motor fuse is

located in the relay and fuse block located on the
back of the junction block)

• Faulty blower motor switch

• Faulty blower motor resistor

• Faulty blower motor relay (front only)

• Faulty blower motor circuit wiring or wire har-

ness connectors

• Faulty high speed blower motor relay (front

only).

VIBRATION

Possible causes of front or rear blower motor vibra-

tion include:

• Improper blower motor mounting

• Improper blower wheel mounting

• Blower wheel out of balance or deformed

• Blower motor faulty.

NOISE

To determine that the rear blower is the source of

the noise, simply switch the blower motor from off to
on. There are no other moving parts involved in the
rear overhead A/C unit, which makes it simple to
identify the source of the noise. To verify that the

front blower is the source of the noise, unplug the
front blower motor wire harness connector and oper-
ate the heater-A/C system. If the noise goes away,
possible causes include:

• Foreign material in the heater-A/C housing

• Improper blower motor mounting

• Improper blower wheel mounting

• Blower motor faulty.

BLOWER MOTOR RELAY

RELAY TEST

The blower motor relay (Voltage Reduction Relay

or VRR) (Fig. 6) is mounted with a single screw
directly to the instrument panel’s structural plastic
inside the glove box opening, next to the left-side
energy-absorbing bracket (Fig. 7). Remove the blower
motor relay to perform the following tests:

(1) A relay in the de-energized position should

have continuity between terminals 87A and 30, and
no continuity between terminals 87 and 30. If OK, go
to Step 2. If not OK, replace the faulty relay.

(2) Resistance between terminals 85 and 86 (elec-

tromagnet) should be 75

6 5 ohms. If OK, go to Step

3. If not OK, replace the faulty relay.

(3) Connect a battery to terminals 85 and 86.

There should now be continuity between terminals
30 and 87, and no continuity between terminals 87A
and 30. If OK, see Relay Circuit Test in the Diagno-
sis and Testing section of this group. If not OK,
replace the faulty relay.

TERMINAL LEGEND

NUMBER

IDENTIFICATION

30

COMMON FEED

85

COIL GROUND

86

COIL BATTERY

87

NORMALLY OPEN

87A

NORMALLY CLOSED

Fig. 6 Blower Motor Relay

DN

HEATING AND AIR CONDITIONING

24 - 15

DIAGNOSIS AND TESTING (Continued)

RELAY CIRCUIT TEST

For circuit descriptions and diagrams, refer to Air

Conditioning/Heater in Wiring Diagrams.

(1) The relay common feed terminal cavity (30) is

connected to fused battery feed directly from a fuse
in the Power Distribution Center (PDC), and should
be hot at all times. Check for battery voltage at the
PDC cavity for relay terminal 30. If OK, go to Step 2.
If not OK, repair the open circuit to the PDC fuse as
required.

(2) The relay normally closed terminal cavity (87A)

is not used for this application. Go to Step 3.

(3) The relay normally open terminal cavity (87) is

connected to the blower motor. When the relay is
energized, terminal 87 is connected to terminal 30
and provides full battery current to the blower motor
feed circuit. There should be continuity between the
PDC cavity for terminal 87 and the blower motor
relay output circuit cavity of the blower motor wire
harness connector at all times. If OK, go to Step 4. If
not OK, repair the open circuit to the blower motor
as required.

(4) The coil battery terminal cavity (86) is con-

nected to the ignition switch. When the ignition
switch is placed in the On position, fused ignition
switch output is directed from a fuse in the junction
block to the relay electromagnetic coil to energize the
relay. There should be battery voltage at the PDC
cavity for relay terminal 86 with the ignition switch
in the On position. If OK, go to Step 5. If not OK,
repair the open circuit to the junction block fuse as
required.

(5) The coil ground terminal cavity (85) is con-

nected to ground. This terminal supplies the ground

for the relay electromagnetic coil. There should be
continuity between the PDC cavity for relay terminal
85 and a good ground at all times. If not OK, repair
the open circuit as required.

ADDITIONAL RELAY CIRCUIT TESTING

• The relay common feed terminal cavity 30 is

connected to the low side of the blower motor. When
the blower switch is Off and the ignition is On, there
should be battery voltage present on this circuit.
When the ignition switch is On, the voltage at that
point should vary based on blower switch position.

• The normally closed contact cavity 87A is con-

nected to the resistor block cavity 3. Check this cir-
cuit by turning the blower switch to High and cycling
between Heat and A/C modes. The voltage in the
Heat mode should be approximately 2 volts. The
blower switch must be in High blower speed position
during this check.

• The normally open contact on cavity 87 is tied to

both the resistor block cavity 6 and the HVAC blower
switch cavity 6. Check for continuity on this circuit.

• The coil B+ contact cavity 86 is connected to an

ignition run start feed. Battery voltage should be
present on this circuit when the ignition switch is in
the Run position.

• The coil ground (–) cavity 85 is connected to the

HVAC switch cavity 2 as well as the JTEC and A/C
high pressure switch. Battery voltage should be
present on this circuit when the ignition switch is in
the Run position and a Heat mode is selected on the
control head. When an A/C mode is selected, the volt-
age at this point should be less than 1 volt.

• If the blower motor does not operate, or only

operates in some modes, check for a faulty connection
at the VRR, or defective blower motor relay (VRR).

BLOWER MOTOR RESISTOR

Both the front blower motor resistor and the

optional rear overhead A/C unit blower motor resistor
can be diagnosed using the procedure that follows.
For circuit descriptions and diagrams, refer to 8W-42
- Air Conditioning/Heater in Group 8W - Wiring Dia-
grams.

WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS,

REFER

TO

GROUP

8M

-

PASSIVE

RESTRAINT SYSTEMS BEFORE ATTEMPTING ANY
STEERING

WHEEL,

STEERING

COLUMN,

OR

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 and isolate the battery negative

cable.

Fig. 7 Blower Motor Relay (VRR) Location

1 – BLOWER MOTOR RESISTOR CONNECTOR
2 – BLOWER MOTOR RELAY
3 – BLOWER MOTOR CONNECTOR
4 – GLOVE BOX LAMP CONNECTOR

24 - 16

HEATING AND AIR CONDITIONING

DN

DIAGNOSIS AND TESTING (Continued)

(2) Unplug the wire harness connector from the

blower motor resistor.

(3) Check for continuity between each of the

blower motor switch input terminals of the resistor
and the resistor output terminal. In each case there
should be continuity. If OK, repair the wire harness
circuits between the blower motor switch and the
blower motor resistor or blower motor as required. If
not OK, replace the faulty blower motor resistor.

BLOWER MOTOR SWITCH

FRONT

For circuit descriptions and diagrams, refer to

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

WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS,

REFER

TO

GROUP

8M

-

PASSIVE

RESTRAINT SYSTEMS BEFORE ATTEMPTING ANY
STEERING

WHEEL,

STEERING

COLUMN,

OR

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) Check for battery voltage at the fuse in the

Power Distribution Center (PDC). If OK, go to Step
2. If not OK, repair the shorted circuit or component
as required and replace the faulty fuse.

(2) Turn the ignition switch to the Off position.

Disconnect and isolate the battery negative cable.
Remove the heater-A/C control from the instrument
panel. Check for continuity between the ground cir-
cuit cavity of the heater-A/C control wire harness
connector and a good ground. There should be conti-
nuity. If OK, go to Step 3. If not OK, repair the open
circuit to ground as required.

(3) With the heater-A/C control wire harness con-

nector unplugged, place the heater-A/C mode control
switch knob to any position except the Off position.
Check for continuity between the ground circuit ter-
minal and each of the blower motor driver circuit ter-
minals of the heater-A/C control as you move the
blower motor switch knob to each of the four speed
positions. There should be continuity at each driver
circuit terminal in only one blower motor switch
speed position. If OK, test and repair the blower
driver circuits between the heater-A/C control con-
nector and the blower motor resistor as required. If
not OK, replace the faulty heater-A/C control unit.

REAR

For circuit descriptions and diagrams, refer to

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

(1) Turn the ignition switch to the Off position.

Disconnect and isolate the battery negative cable.
Remove the rear blower motor switch from the head-
liner. Check for continuity between the ground circuit
cavity of the rear blower motor switch wire harness
connector and a good ground. There should be conti-
nuity. If OK, go to Step 2. If not OK, repair the open
circuit to ground as required.

(2) With the rear blower motor switch wire har-

ness connector unplugged, place the rear blower
motor switch knob to any position except the Off
position. Check for continuity between the ground
circuit terminal and each of the blower motor driver
circuit terminals of the rear blower motor switch as
you move the blower motor switch knob to each of
the three speed positions. There should be continuity
at each driver circuit terminal in only one blower
motor switch speed position. If OK, test and repair
the rear blower driver circuits between the rear
blower motor switch wire harness connector and the
blower motor resistor as required. If not OK, replace
the faulty rear blower motor switch.

COMPRESSOR

When investigating an air conditioning related

noise, you must first know the conditions under
which the noise occurs. These conditions include:
weather, vehicle speed, transmission in gear or neu-
tral, engine speed, engine temperature, and any
other special conditions. Noises that develop during
air conditioning operation can often be misleading.
For example: What sounds like a failed front bearing
or connecting rod, may be caused by loose bolts, nuts,
mounting brackets, or a loose compressor clutch
assembly.

Drive belts are speed sensitive. At different engine

speeds and depending upon belt tension, belts can
develop noises that are mistaken for a compressor
noise. Improper belt tension can cause a misleading
noise when the compressor clutch is engaged, which
may not occur when the compressor clutch is disen-
gaged. Check the serpentine drive belt condition and
tension as described in Cooling System before begin-
ning this procedure.

(1) Select a quiet area for testing. Duplicate the

complaint conditions as much as possible. Switch the
compressor on and off several times to clearly iden-
tify the compressor noise. Listen to the compressor
while the clutch is engaged and disengaged. Probe
the compressor with an engine stethoscope or a long
screwdriver with the handle held to your ear to bet-
ter localize the source of the noise.

(2) Loosen all of the compressor mounting hard-

ware and retighten. Tighten the compressor clutch
mounting nut. Be certain that the clutch coil is
mounted securely to the compressor, and that the

DN

HEATING AND AIR CONDITIONING

24 - 17

DIAGNOSIS AND TESTING (Continued)