To maintain the performance level of the heating, ventilation and air conditioning (HVAC) system, the engine cooling
system must be properly maintained. The use of a bug screen is not recommended. Any obstructions in front of the
radiator or A/C condenser will reduce the performance of the A/C and engine cooling systems.

The engine cooling system includes the radiator, thermostat, radiator hoses and the engine coolant pump. Refer to
7 - Cooling for more information before opening or attempting any service to the engine cooling system.

All vehicles are equipped with a common heater, ven-
tilation and air conditioning (HVAC) housing (1). The
heating-A/C system combines A/C, heating, and venti-
lating capabilities in a single HVAC housing mounted
within the passenger compartment behind the instru-
ment panel. The HVAC housing includes:

•

Heater core (2)

•

Blend-air doors and actuator (3)

•

A/C evaporator (4)

•

Blower motor resistor (5)

•

Recirculation-air door and actuator (6)

•

Blower motor (7)

•

Evaporator temperature sensor (8)

•

Mode-air doors and actuators (9)

Based upon the mode selected, conditioned air can exit the HVAC housing through one or a combination of the
three main housing outlets: defrost, panel or floor. The defrost and panel outlets are located on the top of the HVAC
housing and the floor outlet is located on the bottom of the HVAC housing. Once the conditioned air exits the HVAC
housing, it is further directed through molded plastic ducts to the outlets within the vehicle interior. These outlets and
their locations are as follows:

•

Defroster Outlet - A single large defroster outlet is located in the center of the instrument panel top cover,
near the base of the windshield.

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HVAC - SERVICE INFORMATION

•

Side Window Demister Outlets - There are two side window demister outlets, one is located at each out-
board end of the instrument panel face near the A-pillars.

•

Panel Outlets - There are four panel outlets in the instrument panel, one located near each outboard end of
the instrument panel facing the rear of the vehicle and two located at the top of the instrument panel center
bezel.

•

Floor Outlets - There are two floor outlets, one located above each side of the floor panel center tunnel near
the dash panel.

OPERATION

The heating-A/C system used in this vehicle is a single zone, blend-air type system. In this blend-air heating-A/C
system, two blend-air doors control the amount of conditioned air that is allowed to flow through, or around, the
heater core. A temperature control determines the discharge air temperature by operating an electric actuator, which
operates the blend-air doors. This allows an almost immediate control of the output air temperature of the system.
The A/C system is designed for the use of non-CFC, R-134a refrigerant and uses an A/C evaporator to cool and
dehumidify the incoming air prior to blending it with the heated air.

The heating-A/C system pulls outside (ambient) air
through the cowl opening at the base of the wind-
shield, then into the air inlet housing and through the
A/C evaporator (3). Air flow can be directed either
through or around the heater core (1). This is done by
adjusting the blend-air doors (2) with the temperature
controls located on the A/C-heater control in the
instrument panel. The air flow can then be directed
from the panel, floor and defrost outlets in various
combinations using the mode control located on the
A/C-heater control. Air flow velocity can be adjusted
with the blower speed control located on the A/C-
heater control.

The outside (fresh) air intake can be shut off by selecting the Recirculation Mode with the mode control. This will
operate an electrically actuated recirculation-air door (4) that closes off the fresh air intake and recirculates the air
that is already inside the vehicle.

The A/C compressor can be engaged in any mode by pressing the snowflake, A/C on/off button. It can also be
engaged by placing the mode control in the mix to defrost positions. This will remove heat and humidity from the air
before it is directed through or around the heater core. The mode control on the A/C-heater control is used to also
direct the conditioned air to the selected system outlets. The mode control uses two electric actuators to control the
mode-air doors (5 and 6).

The defroster outlet receives airflow from the HVAC housing through the molded plastic defroster duct, which con-
nects to the HVAC housing defroster outlet. The airflow from the defroster outlet is directed by fixed vanes in the
defroster outlet grille and cannot be adjusted. The defroster outlet grille is serviceable from the instrument panel.

The side window demister outlets receive airflow from the HVAC housing through the molded plastic demister ducts.
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 bi-level, floor, floor-defrost and defrost
settings. The airflow from the side window demister outlets is directed by fixed vanes in the demister outlet grilles
and cannot be adjusted. The demister outlet grilles are only serviced with the instrument panel outlets.

The instrument panel outlets receive airflow from the HVAC housing through a molded plastic center distribution
duct, center panel duct and two end panel ducts. The two end panel ducts direct airflow to the left and right instru-
ment 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 duct. The front floor outlets are
integral to the molded plastic floor distribution duct, which is secured to the bottom of the HVAC housing. The floor
outlets cannot be adjusted.

HVAC - SERVICE INFORMATION

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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.

This A/C system uses an A/C orifice tube 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 A/C evaporator and supplies an evaporator temperature signal to the A/C-heater control. The
A/C-heater control broadcasts the A/C request on the controller area network (CAN) B bus, where it is read and
processed by the front control module (FCM), which in turn broadcasts it on the CAN C bus, where it is read and
processed by the powertrain control module (PCM) which cycles the A/C clutch relay as necessary.

DIAGNOSIS AND TESTING

HEATING-A/C SYSTEM DIAGNOSTICS

CAUTION: Do not exchange A/C Heater Controls from vehicle to vehicle. Software versions differ between
models and model years. Installing an A/C Heater Control with software that is incompatible for a given
vehicle can result in either improper or failed HVAC system operation.

ON-BOARD DIAGNOSTICS

The A/C-heater control communicates on the controller area network (CAN) B bus and is fully addressable with a
scan tool.

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 a scan tool. Refer to 24 - HVAC - Elec-
trical Diagnostics for HVAC DTC 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, Actuator Calibration, and Actuator DTC Detection. 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 a scan tool.

•

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

•

will fail if evaporator temperature is below 18.3° C (65° F) when initiating the test.

•

will pass if the evaporator temperature drops 11.1° C (20° F).

•

indicates an outcome by displaying one or more test status messages on the scan tool. These test status
messages will clear after paging back out of this test function. Therefore, is it important to note all of the mes-
sages before doing so.

•

will cause the A/C status indicator to flash while the test is running.

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HVAC - SERVICE INFORMATION

ACTUATOR CALIBRATION FUNCTION

The Actuator Calibration function:

•

is actuated with a scan tool.

•

homes and repositions door actuators.

•

monitors for door span faults. Door span faults (XXX Door Travel Range Too Large or XXX Door Travel Range
Too Small) will only display after calibration.

•

will cause the electric backlight (EBL) status indicator (if equipped) to flash while the test is running.

ACTUATOR DTC DETECTION TEST

The Actuator DTC Detection Test:

•

is actuated with a scan tool.

•

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. Shorted actuator circuit faults (XXX Control Circuit High or XXX Control Circuit Low) will only
display after running the Actuator DTC Detection Test.

After repairing each DTC, cycle the ignition switch, and then run the Actuator DTC Detection Test again to ensure
that no new DTCs exist. If multiple DTCs are present, beginning with the common circuit, diagnose and repair all
short high faults and then short low faults. When the test returns passed, clear all faults and run the Actuator Cal-
ibration function 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.

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 of the vehicle and the location where the vehicle will be tested
must be a minimum of 21° C (70° F) for this test. Also the evaporator temperature sensor probe (located between
the evaporator fins) must be a minimum of 18° C (65° F) for this test as well.

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, which is 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 power-
train control module (PCM), go to Step 2. If any DTCs are found, repair as required, then proceed to Step 2.

HVAC - SERVICE INFORMATION

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