Procedure - All Models

Vacuum Test Charts are provided herein for all models. When testing an A/C-Heater system for proper vacuum control of the various doors and valves, locate and use the specific Vacuum Test Chart applicable to the car model being tested. Further, use the Code Number Chart on the first page of this article to quickly and easily identify each door, function, lever control, and how the door is actuated.

Procedure for testing the vacuum control system is identical for all models. Proceed as follows:

1. With the engine warm and running, connect a vacuum gauge in the main (black) vacuum supply line between the check valve and the vacuum selector valve.
2. Move the control levers on the control panel to the position shown on the last line of the Vacuum Test Chart (except Montego and Torino, where the levers are placed in the position listed on the third line from the bottom). Notice on the applicable Test Chart that with the control levers in this initial test position, no vacuum is applied to any of the vacuum motors. 
3. Noting the vacuum reading at the gauge, quickly turn the ignition key to ACCESSORY position and check the vacuum gauge for any vacuum loss. If a leak is indicated at this control lever position by a vacuum loss, the leak is in either the vacuum supply line or the check valve. If no vacuum loss is noted at this time, proceed to step 4).
4. In turn, position the control levers as shown on each line of the Test Chart. Note the vacuum gauge reading in each position, as the ignition key is quickly turned to the ACCESSORY position. If a vacuum loss is noted in any of the control lever positions, use the Test Chart to isolate the door or valve, the particular vacuum line, and the vacuum motor concerned. Use of a vacuum gauge connected to a vacuum line where it is connected to a vacuum motor will determine if there is a leak in the vacuum line between the motor and the vacuum selector valve. If there is no vacuum at a vacuum motor a kinked or plugged line is indicated.
5. If a door or valve is inoperative and no vacuum loss is indicated on the vacuum gauge, check the air door or valve for binding or mechanical interference. If the door or valve moves freely and if vacuum is available at the motor connection, then the motor is defective and must be replaced.
6. If no vacuum loss is noted in any of the lever positions shown on the Test Chart, and all vacuum motors and doors function as indicated on the Code Number Chart the system may be considered to be operating properly.