Vacuum Tests

VACUUM SYSTEM DIAGNOSIS
1. To test the EATC vacuum system, start the engine and depress the function buttons slowly from one position to another.
a. 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.
b. 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.

NOTE: To test the control assembly vacuum valve, apply 50 kPa (15 in Hg) of vacuum to the number five terminal.

EATC System Vacuum Schematic And Selector Test:

2. If a momentary hiss cannot be heard as each function button is depressed from one 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.
3. 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.

EATC System Airflow Schematic:

EATC Vacuum Control Motor Test Chart:

4. Cycle the function buttons through each position with the blower on HI and check the location(s) of the discharge air.
a. The Airflow Schematic and the Vacuum Control Motor Test Chart shows the vacuum motors applied for each function selection along with an airflow diagram of the system.
b. 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.
c. If a vacuum motor fails to operate, the motor can readily be found because the airflow will be incorrect.
5. If a vacuum motor is inoperative, check the operation of the motor with a Rotunda Vacuum Tester 021-00014 or equivalent. If the vacuum motor operates properly, the vacuum hose is probably pinched, kinked, disconnected, or has a leak.
6. If the 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.

NOTE: To check the electrical system operation between the control head connector and the blend door actuator, refer to the Electrical System Diagnostic Procedures. EATC Self Test-Control Head Connector and Blend Door Actuator