Dodge Nitro. Manual — part 729

output air temperature.

Fig. 2: Blend Air System Schematic
Courtesy of CHRYSLER LLC

The heating-A/C system pulls outside (ambient) air through the fresh air intake (4) located at the cowl panel at
the base of the windshield and into the air inlet housing above the heating, ventilation and air conditioning
(HVAC) housing and passes through the A/C evaporator (7). Air flow is then directed either through or around
the heater core (2). This is done by adjusting the position of the blend-air door (3) with the temperature control
located on the A/C-heater control in the instrument panel. Air flow is then directed out the floor outlet (8),
instrument panel outlet (10) or the defroster outlet (1) in various combinations by adjusting the position of the
mode-air doors (9 and 11) using the mode control located on the A/C-heater control. The temperature and mode
control uses electrical actuators to operate the air doors.

The velocity of the air flow out of the outlets can be adjusted with the blower speed control located on the A/C-
heater control.

The fresh air intake can be shut off by pressing the Recirculation button on the A/C-heater control. This will
operate the electrically actuated recirculation-air door (5), which closes off the fresh air intake. With the fresh
air intake closed, the conditioned air within the vehicle is pulled back into the HVAC housing through the
recirculation air intake (6).

The A/C compressor can be engaged by pressing the A/C (snowflake) button on the A/C-heater control when
the mode control is set in any floor to instrument panel position. The A/C compressor will automatically engage
when the mode control is set in any Mix to Defrost position. This is done to help reduce fogging of the front
windows by removing humidity from the conditioned air prior to it coming into contact with the windows.

The defroster outlet receives airflow from the HVAC housing through the molded plastic defroster duct. The
airflow from the defroster outlet is directed by fixed vanes in the defroster outlet grille and cannot be adjusted.

NOTE:

Typical blend-air type HVAC system shown.

2007 Dodge Nitro R/T

2007 HVAC Heating & Air Conditioning - Service Information - Nitro

The side window demister outlets receive airflow from the HVAC housing through the defroster duct and
molded plastic demister ducts which are integral to the instrument panel. The airflow from the side window
demister outlets is directed by fixed vanes in the demister outlet grilles and cannot be adjusted. The demisters
direct air from the HVAC housing through the outlets located on the top corners of the instrument panel. The
demisters operate when the mode control is positioned in the floor-defrost and defrost-only settings. Some air
may be noticeable from the demister outlets when the mode control is in the bi-level to floor positions.

The panel outlets receive airflow from the HVAC housing through the center panel duct and the two molded
plastic panel ducts, which are integral to the instrument panel. The two end ducts direct airflow to the left and
right instrument panel outlets, while the center panel duct directs airflow to the two center panel outlets. Each of
these outlets can be individually adjusted to direct the flow of air.

The floor outlets receive airflow from the HVAC housing through the floor distribution ducts. The front floor
outlets are integral to the molded plastic floor ducts, which are secured to the sides of the HVAC housing. The
floor outlets cannot be adjusted.

This A/C system uses an A/C expansion valve 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 temperatures and prevent evaporator freezing, an evaporator temperature sensor is used.
The sensor is located downstream of the evaporator and supplies an evaporator temperature signal to the A/C-
heater control.

DIAGNOSIS AND TESTING

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
important to understand the effect that humidity has on the performance of the A/C system. When humidity is

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 objectionable 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.

2007 Dodge Nitro R/T

2007 HVAC Heating & Air Conditioning - Service Information - Nitro

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.

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 system 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 minimum of 21°C (70°F) for this test.

A/C PERFORMANCE TEST

1. Check for diagnostic trouble codes using a scan tool. If no DTCs are found in the powertrain control

module (PCM) or engine control module (ECM), depending on engine application, go to step 2

2. Connect a tachometer and a manifold gauge set or an A/C recycling/charging station.

3. Operate the heating-A/C system under the following conditions.

Engine at 1,000 RPM at operating temperature

Door or windows open

Transmission in Park or Neutral with parking brake set (depending on transmission application)

A/C-heater controls set to Recirculation mode (max-A/C), full cool, panel mode, high blower and
with A/C compressor engaged. If the A/C compressor does not engage, see the A/C System
Diagnosis chart.

4. Insert a thermometer in the driver side center panel air outlet and operate the vehicle a minimum of ten

minutes to allow the thermometer temperature to stabilize.

WARNING:

Refer to the applicable warnings and cautions for this system before
performing the following operation. See WARNING, and CAUTION. Failure
to follow the warnings and cautions could result in possible serious or
fatal injury.

CAUTION: The use of an A/C recycling/charging station for purposes of determining

the actual charge level of an A/C system is not recommend. Service
recycling/charging stations do not reflect the correct amount of refrigerant
charge in the A/C system after a single "reclaim" cycle. Tests have shown
that it takes up to 3 or 4 "reclaim" cycles to remove all of the refrigerant
charge. Use only the following procedure for determining the proper
charge level.

NOTE:

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

2007 Dodge Nitro R/T

2007 HVAC Heating & Air Conditioning - Service Information - Nitro

5. 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 Temperature and Pressure chart.
The compressor clutch may cycle, depending upon the ambient temperature and humidity. If the clutch
cycles, use the readings obtained before the clutch disengaged.

A/C PERFORMANCE TEMPERATURE AND PRESSURE

6. 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 System Diagnosis
chart.

A/C SYSTEM DIAGNOSIS

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)

Condenser
Outlet 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)

Condition

Possible Causes

Correction

Rapid A/C clutch cycling
(ten or more cycles per
minute).

1. Low refrigerant system
charge.

1. See REFRIGERANT SYSTEM LEAKS.
Test the refrigerant system for leaks. Repair,
evacuate and charge the refrigerant system as
required.

Equal pressures, but the A/C
clutch does not engage.

1. No refrigerant in the
refrigerant system.

1. See REFRIGERANT SYSTEM LEAKS.
Test the refrigerant system for leaks. Repair,
evacuate and charge the refrigerant system as
required.

2. Open fuse.

2. Check the fuses in the power distribution
center and the junction block. Repair the
shorted circuit or component and replace the
fuses as required.

3. Inoperative A/C clutch
field coil.

3. See A/C Compressor Clutch in this group.
Test the A/C clutch field coil and replace as
required.

4. Inoperative A/C clutch
relay.

4. See CLUTCH-A/C COMPRESSOR . Test
the A/C clutch relay and relay circuits. Repair
the circuits or replace the relay as required.

5. Improperly installed or

5. See TRANSDUCER-A/C PRESSURE.

2007 Dodge Nitro R/T

2007 HVAC Heating & Air Conditioning - Service Information - Nitro