- Perform the Self Diagnostic Test. Record all error codes displayed during the test.
- If error codes appear during the Self Diagnostic Test, follow the diagnostic procedures indicated in the Error Code Key.
- If a malfunction exists but no error code appears during the Self Diagnostic Test, perform the Functional Test.
The control assembly will detect electrical malfunctions occurring during the self-test.
- Make sure the coolant temperature is at least 120°F (49°C).
- To display error codes, push the OFF and FLOOR buttons simultaneously and then the AUTOMATIC button within 2 seconds. The test may run as long as 20 seconds, during which time the display will be blank. If the display is blank for more than 20 seconds, consult the No Error Code Found Diagnosis and Testing chart.
- The Self-Diagnostic Test can be initiated at any time with the resulting error codes being displayed. Normal operation of the system stops when the Self-Diagnostic Test is activated. To exit the self-test and restart the system, push the COOLER button. The self-test should be deactivated before powering the system down.
The Functional Test is designed to catch those system failures that the self-test is unable to test.
- Make sure the engine is cold.
- The in-vehicle temperature should be greater than 50°F (10°C) for proper evaluation of system response.
- Follow the instructions in each step of the Functional Test.
VACUUM SYSTEM DIAGNOSIS
To test the automatic temperature control vacuum system, start the engine and depress the function buttons slowly from one position to another. A momentary hiss should be heard as each button is depressed from one position to another, indicating that vacuum is available at the control assembly. A continuous hiss at the control assembly indicates a major leak somewhere in the system. It does not necessarily indicate that the leak is at the control assembly.
If a momentary hiss cannot be heard as each function button is depressed from 1 position to another, check for a kinked, pinched or disconnected vacuum supply hose. Also, inspect the check valve between the vacuum intake manifold and the vacuum reservoir to ensure it is working properly.
If a momentary hiss can be heard as each function button is depressed from one position to another, vacuum is available at the control assembly. Cycle the function buttons through each position with the blower on HI and check the location(s) of the discharge air. The airflow schematic and vacuum control chart shows the vacuum motors applied for each function selection along with an airflow diagram of the system. The airflow diagram shows the position of each door when vacuum is applied and their no-vacuum position. With this chart, airflow for each position of the control assembly can be determined. If a vacuum motor fails to operate, the motor can readily be found because the airflow will be incorrect.
If a vacuum motor is inoperative, check the operation of the motor with a vacuum tester. If the vacuum motor operates properly, the vacuum hose is probably kinked, pinched, disconnected or has a leak.
If the function system functions normally at idle, but goes to defrost during acceleration, a small leak exists in the system. The leak can best be located by shutting OFF the engine and using a gauge to check for vacuum loss while selectively blocking off vacuum hoses.