REAR SYSTEM
The rear heating-A/C system pulls interior air through the opening in the rear quarter interior trim panel and into the
rear blower motor in the rear HVAC housing, then through the rear A/C evaporator. Air flow can be directed either
through or around the rear heater core. This is done by adjusting the blend-air door with either the front or the rear
temperature control (depending on the front A/C-heater control setting). The air flow is then automatically directed to
the floor or ceiling outlets depending on the conditioned air temperature selected by the rear mode-air door. Air flow
velocity can be adjusted with the blower speed control located on either the front A/C-heater control or the rear
A/C-heater control (depending on the front A/C-heater control setting).
The headliner air outlets receive airflow from the rear HVAC housing through the molded plastic ceiling duct, which
connects to the headliner duct and headliner air outlets. Airflow direction from the headliner air outlets can be
adjusted by moveable vanes and the headliner air outlets can be serviced separately.
The rear floor outlet receives airflow from the rear HVAC housing through the molded plastic floor distribution duct,
which connects to the rear floor outlet located in the rear quarter interior trim panel. The airflow from the rear floor
outlet is directed by fixed vanes in the outlet and air flow direction cannot be adjusted. The rear floor outlet is inte-
gral to the rear quarter interior trim panel.
This rear A/C system uses an “H” valve-type thermal expansion valve (TXV) to meter the flow of refrigerant to the
rear A/C evaporator.
DIAGNOSIS AND TESTING
HEATING-A/C SYSTEM DIAGNOSTICS
ON-BOARD 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.
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. All DTCs must be read with a scan tool. Refer to 24 - HVAC -
Electrical 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 Calibration Function, the Actuator DTC Detection Test. 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 system test to perform when diagnosing a given 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).
HB
HVAC - SERVICE INFORMATION
24 - 325