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Discussion Starter · #1 ·
I have a 2008 Crown Vic with what I am sure is an air conditioning vent vacuum problem. The problem started recently after 40,000 miles of great service. When the air conditioning is on the air flows through the defroster instead of the front vents. When you let it idle for a while, the vents open slightly. Upon acceleration, the vents close. When you decelerate, they try to open again. I am sure I have a vacuum leak or a bad switch. A local mechanic told me he suspects a bad one-way valve. I am a decent amateur mechanic and would like to fix this myself. I looked under the hood and suspect the vacuum switches are located behind the dash. How can I access these lines and switches? Thanks!
 

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The easiest way I have found, is to access the control head. Once you have access, you will find the vacuum source, and all the vacuum circuits to be represented there. Do you have a handheld vacuum tester? Can you borrow one? Maybe rent one from an Autozone or other large parts chain?

The idea is to test each leg of the vacuum circuit. Diagnose by isolation.
Start with the vacuum source. How much vacuum do you have available? How much when you drive under acceleration? Tee the vacuum tester into the vacuum source, then reattatch. How much vacuum now? Same? Lower? With your tester apply vacuum to each leg. Does it hold? Do the actuators move? Did the airflow change?

Last week I replaced an EATC control for a '04 Gran Marq due to vacuum leakage. Symptoms were quite similar to yours. A new control was $600 from Ford. You can bet I repeated my tests several times to be verify the failure, and diagnosis.

The new control worked flawlessly.

This could be helpful:
http://www.fordforumsonline.com/forum/engine-drivetrain/94-locate-vacuum-leak.html
 

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The control head is the push button control in the center of your dash. Remove the trim pieces that surround the control, remove the 4 retaining screws that mount the control, and look at the back. IIRC you will see 2 electrical connectors, and 1 vacuum connector.
 

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Discussion Starter · #5 ·
My problem is the control head. I read some old threads and there are actually three ways to fix it.

1. Buy a new control head for $600-$800 and wait for the new one to fail

2. Splice the black feed hose and the blue and white hoses together using a tee fitting. This opens the vents all the time. Since I live in Florida and rarely use the defroster or floor vents, I opted for this fix for now.

3. Splice in a manual control head from a police car or similar. I have been told you can buy one of these for about $50. If I ever long for the defroster, I'll go this route.

Thanks for all the help. This forum is awesome!



 
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