Heating-A/C System Diagnostics

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.

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.

SYSTEM TESTS

HVAC System Test

The HVAC System Test, found in 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

NOTE: The work area ambient temperature must be above 21° C (70° F) and the evaporator temperature must be above 10° C (50° F) prior to conducting the 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.
- is performed with controls set to full cool and high blower and with windows open.
- will fail if evaporator temperature is below 10° C (50° F) when initiating the test.
- will pass if the evaporator temperature drops 11° 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 messages before doing so.
- will cause the A/C status indicator to flash while the test is running.

ACTUATOR CALIBRATION FUNCTION

The Actuator Calibration function:

- is actuated with a scan tool.
- clears all actuator related DTCs when the test is actuated.
- 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 - DUAL-ZONE

The Actuator DTC Detection Test:

- is actuated with a scan tool.
- clears all actuator related DTCs when the test is actuated.
- supplements the continuous diagnostics on the actuator drive system.
- monitors for shorted actuator circuits allowing service to easily diagnose and troubleshoot up to three simultaneous 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 passenger blend door, diagnose and repair all short high faults and then short low faults. When the test returns passed, clear all faults and run the Actuator Calibration function as a final check of system health.

ACTUATOR DTC DETECTION TEST - SINGLE-ZONE

The Actuator DTC Detection Test:

- is actuated with a scan tool.
- clears all actuator related DTCs when the test is actuated.
- supplements the continuous diagnostics on the actuator drive system.
- monitors for shorted actuator circuits allowing service to easily diagnose and troubleshoot up to three simultaneous 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 Calibration function as a final check of system health.