Dodge Ram Truck 1500-2500-3500. Manual — part 2048

NOTE: It is important to keep the air intake opening clear of debris. Leaf particles and other debris that is
small enough to pass through the cowl opening screen can accumulate within the HVAC housing. The
closed, warm, damp and dark environment created within the housing is ideal for the growth of certain
molds, mildews and other fungi. Any accumulation of decaying plant matter provides an additional food
source for fungal spores, which enter the housing with the fresh intake-air. Excess debris, as well as objec-
tionable odors created by decaying plant matter and growing fungi can be discharged into the passenger
compartment during heater-A/C operation if the air intake opening is not kept clear of debris.

The A/C system on models so equipped is designed for the use of non-CFC, R-134a refrigerant and uses an A/C
fixed orifice tube located in the liquid line to meter the flow of refrigerant to the A/C evaporator. The A/C evaporator
cools and dehumidifies the incoming air prior to blending it with the heated air. To maintain minimum evaporator
temperature and prevent evaporator freezing, an evaporator temperature sensor is used to supply evaporator tem-
perature input to the A/C-heater control. The powertrain control module (PCM) cycles the A/C compressor clutch off
and on as necessary to protect the A/C system from evaporator freezing and optimize A/C system performance.

DIAGNOSIS AND TESTING

HEATING-A/C SYSTEM DIAGNOSTICS

ON-BOARD DIAGNOSTICS

The A/C-heater control communicates on the Programmable Communication Interface Multiplex System (PCI) Bus
and is fully addressable with the DRBIII

T

.

The A/C-heater control’s primary means of fault detection is through active and stored diagnostic trouble codes
(DTCs). Active DTCs are those which currently exist in the system. The condition causing the fault must be repaired
in order to clear this type of DTC. Stored DTCs are those which occurred in the system since the A/C-heater control
received the last clear diagnostic info message. DTCs must be read with the DRBIII

T

. Refer to 24 - HVAC - Elec-

trical Diagnostics for the diagnostic test procedures.

The A/C-heater control’s secondary means of fault detection is through system tests. These tests include the HVAC
System Test, the A/C Cooldown Test, the Actuator Circuit Test, and HVAC Door Recalibration. Refer to System Tests
in this Section for a detailed description of each test.

SYSTEM TESTS

HVAC System Test

The HVAC System Test, found in 24 - HVAC - Electrical Diagnostics, provides a starting point in the diagnostic
process by identifying the appropriate diagnostic procedure or system test to perform when diagnosing a given
symptom, condition, or DTC. It also provides a means for testing the entire HVAC system by utilizing the A/C-heater
control’s On-Board System Tests. The On-Board System Tests can also assist in diagnosing stored DTCs.

A/C Cooldown Test

The A/C Cooldown Test:

•

is actuated with the DRBIII

T

.

•

tests A/C system performance based on evaporator temperature sensor input.

•

will not run if ambient temperature is below 12.7° C (55° F).

•

will pass if the evaporator temperature drops 11.1° C (20° F) within one minute of starting the test.

•

indicates an outcome by displaying one or more test status messages on the DRBIII

T

. These test status mes-

sages will clear after paging back out of this test function. Therefore, is it important to note all of the messages
before doing so.

Running the A/C Cooldown Test will cause the A/C status indicator to flash. If the test fails, the A/C status indicator
will continue to flash until either the test returns passed or the ignition key is cycled. When the A/C status indicator
is flashing, it will not indicate A/C operating status. However, the A/C mode switch will continue to function normally.
For vehicles equipped with electric backlight (EBL), when the A/C status indicator is flashing, the EBL status indi-
cator will not function. However, the EBL mode switch will continue to function normally.

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HVAC - SERVICE INFORMATION

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HVAC Door Recalibration

The HVAC Door Recalibration:

•

is actuated with the DRBIII

T

.

•

homes and repositions door actuators.

•

monitors for door span faults.

•

indicates an outcome by displaying one or more messages on the DRBIII

T

.

For vehicles equipped with electric backlight (EBL), running the HVAC Door Recalibration will cause the EBL status
indicator to flash. If recalibration fails, the EBL status indicator will continue to flash until either the system passes
recalibration or the ignition key is cycled. When the EBL status indicator is flashing, it will not indicate EBL operating
status. However, the EBL mode switch will continue to function normally. When the EBL status indicator is flashing,
the A/C status indicator will not function. However, the A/C mode switch will continue to function normally.

For vehicles not equipped with electric backlight (EBL), no status indicator will flash when running the HVAC Door
Recalibration. If recalibration fails, the A/C status indicator will not function, however, the A/C mode switch will con-
tinue to function normally.

Actuator Circuit Test

The Actuator Circuit Test:

•

is actuated with the DRBIII

T

.

•

supplements the continuous diagnostics on the actuator drive system.

•

monitors for shorted actuator circuits allowing service to easily diagnose and troubleshoot up to three simul-
taneous shorts.

•

indicates an outcome by displaying up to three messages on the DRBIII

T

.

Understanding Actuator Circuit Test Fault Messages

•

A Short Too Complex fault message indicates that a specific determination of which lines are shorted could not
be made. This fault is caused by more than three drivers being shorted in the same direction (e.g., four drivers
all shorted to ground, or two or more drivers shorted with at least one driver shorted to ignition/battery and one
driver shorted to ground).

•

Fault messages displaying XXX Driver/Circuit Shorted to Ignition/Battery and XXX Driver/Circuit Shorted to
Ground will set on a per-driver basis.

•

Fault messages displaying the same two drivers/circuits shorted to ignition/battery as-well-as shorted to ground
indicates that two actuator driver circuits are shorted together.

When Performing The Actuator Circuit Test

•

To ensure a proper diagnosis, repair all Short Too Complex fault messages first, all common door driver circuit
related fault messages second, and all other fault messages last.

•

After repairing each fault, cycle the ignition switch, then run the Actuator Circuit Test again to ensure that no
new faults exist. When the test returns passed, clear all faults and run the HVAC Door Recalibration as a final
check of system health.

A/C PERFORMANCE

The A/C system is designed to provide the passenger compartment with low temperature and low humidity air. The
A/C evaporator, located in the HVAC housing is cooled to temperatures near the freezing point. As warm damp air
passes over the fins of the A/C evaporator, the air transfers its heat to the refrigerant in the evaporator coils and the
moisture in the air condenses on the evaporator fins. During periods of high heat and humidity, an A/C 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 A/C evaporator. As the passenger compartment air dehumidifies, the
A/C system performance levels rise.

Humidity has an important bearing on the temperature of the air delivered to the interior of the vehicle. It is impor-
tant to understand the effect that humidity has on the performance of the A/C system. When humidity is high, the
A/C 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 evaporator fins. Condensing the moisture in the air transfers heat
energy into the evaporator fins and coils. This reduces the amount of heat the A/C evaporator can absorb from the
air. High humidity greatly reduces the ability of the A/C evaporator to lower the temperature of the air.

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However, evaporator capacity used to reduce the amount of moisture in the air is not wasted. Wringing 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 A/C system on humid days. A performance test is the best way to determine whether the sys-
tem is performing up to design standards. This test also provides valuable clues as to the possible cause of trouble
with the A/C system. The ambient air temperature in the location where the vehicle will be tested must be a mini-
mum of 21° C (70° F) for this test.

A/C PERFORMANCE TEST

WARNING: Refer to the applicable warnings and cautions for this system before performing the following
operation (Refer to 24 - HEATING & AIR CONDITIONING/PLUMBING - WARNINGS) and (Refer to 24 - HEAT-
ING & AIR CONDITIONING/PLUMBING - CAUTIONS). Failure to follow the warnings and cautions could result
in possible personal injury or death.

NOTE: When connecting the service equipment coupling to the line fitting, verify that the valve of the cou-
pling is fully closed. This will reduce the amount of effort required to make the connection.

1. Perform the A/C System Performance Test found within the HVAC System Test (refer to 24 - HVAC Electrical

Diagnostics). If no diagnostic trouble codes (DTCs) are found in the A/C-heater control or the powertrain control
module (PCM), go to Step 2. If any DTCs are found, repair as required, then proceed to Step 2.

2. Connect a tachometer and a manifold gauge set.

3. Set the A/C-heater control to the Recirculation mode (max-A/C) position, the temperature control to the full cool

position, and the blower motor control to the highest speed position.

4. Start the engine and hold the idle at 1,000 rpm with the compressor clutch engaged. If the A/C compressor does

not engage, see the A/C Diagnosis chart.

5. The engine should be at operating temperature, the doors should be closed and the windows opened.

6. Insert a thermometer in the driver side center panel outlet and operate the A/C system until it stablizes.

NOTE: The A/C compressor clutch may cycle, depending upon the ambient temperature and humidity.If the
clutch cycles, use the readings obtained before the clutch disengaged.

7. With the A/C compressor clutch engaged, compare the air temperature at the center panel outlet and the A/C

compressor discharge pressure (high side) to the A/C Performance and Pressure chart.

PERFORMANCE TEMPERATURE AND PRESSURE

Ambient Air
Temperature

21° C

(70° F)

27° C

(80° F)

32° C

(90° F)

38° C

(100° F)

43° C

(110° F)

Air Temperature at
Center Panel Outlet

7° C

(45° F)

7° C

(45° F)

13° C

(55° F)

13° C

(55° F)

18° C

(64° F)

Compressor Inlet
Pressure at Service
Port (low Side)

138 to 207 kPa

(20 to 30 psi)

172 to 241 kPa

(25 to 35 psi)

207 to 276

kPa

(30 to 40 psi)

241 to 310

kPa

(35 to 45 psi)

276 to 345 kPa

(40 to 50 psi)

Compressor
Discharge Pressure at
Service Port (High
Side)

1034 to 1724

kPa

(150 to 250

psi)

1379 to 2068

kPa

(200 to 300

psi)

1724 to 2413

kPa

(250 to 350

psi)

1999 to 2689

kPa

(290 to 390

psi)

2413 to 2965

kPa

(350 to 430 psi)

8. If the air outlet temperature fails to meet the specifications in the A/C Performance Temperature and Pressure

chart, or if the A/C compressor discharge pressure is high, refer to the A/C Pressure Diagnosis chart.

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HVAC - SERVICE INFORMATION

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A/C PRESSURE DIAGNOSIS

Condition

Possible Causes

Correction

Constant compressor

engagement and warm air

from passenger vents.

1. Low refrigerant system

charge.

1. See Refrigerant System Leaks in this group.
Test the refrigerant system for leaks. Repair,
evacuate and charge the refrigerant system, if
required.

Equal pressures, but the
compressor clutch does not
engage.

1. No refrigerant in the
refrigerant system.

1. See Refrigerant System Leaks in this group.
Test the refrigerant system for leaks. Repair,
evacuate and charge the refrigerant system, if
required.

2. Faulty fuse.

2. Check the fuses in the Power Distribution
Center and the junction block. Repair the shorted
circuit or component and replace the fuses, if
required.

3. Faulty A/C compressor
clutch coil.

3. See A/C Compressor Clutch Coil in this group.
Test the compressor clutch coil and replace, if
required.

4. Faulty A/C compressor
clutch relay.

4. See A/C Compressor Clutch Relay in this
group. Test the compressor clutch relay and relay
circuits. Repair the circuits or replace the relay, if
required.

5. Improperly installed or
faulty Evaporator
Temperature Sensor.

5. See Evaporator Temperature Sensor in this
group. Reinstall or replace the sensor as
required.

6. Faulty A/C pressure
transducer.

6. See A/C pressure transducer in this group.
Test the switch and replace, if required.

7. Faulty Powertrain Control
Module (PCM).

7. (Refer to Appropriate Diagnostic Information).
Test the PCM and replace, if required.

Normal pressures, but A/C
Performance Test air
temperatures at center panel
outlet are too high.

1. Excessive refrigerant oil in
system.

1. See Refrigerant Oil Level in this group.
Recover the refrigerant from the refrigerant
system and inspect the refrigerant oil content.
Restore the refrigerant oil to the proper level, if
required.

2. Blend door inoperative or
sealing improperly.

2. See Blend Door in this group. Inspect the
blend door for proper operation and sealing and
correct, if required.

3. Blend door actuator faulty
or inoperative.

3. Perform blend door actuator diagnosis, replace
if faulty.

The low side pressure is
normal or slightly low, and the
high side pressure is too low.

1. Low refrigerant system
charge.

1. See Refrigerant System Leaks in this group.
Test the refrigerant system for leaks. Repair,
evacuate and charge the refrigerant system, if
required.

2. Refrigerant flow through
the accumulator is restricted.

2. See Accumulator in this group. Replace the
restricted accumulator, if required.

3. Refrigerant flow through
the evaporator coil is
restricted.

3. See A/C Evaporator in this group. Replace the
restricted evaporator coil, if required.

4. Faulty compressor.

4. See A/C Compressor in this group. Replace
the compressor, if required.

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