vacume leek , all hoses are good, where should i look next? on 2003 Ford E-250

humming sound coming from air intake at idle ,During accelerating the ac stops blowing through cabin vents and starts blowing through floor and defrost vents.

by in Pearland, TX on April 16, 2011
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2 answers 1 comment
ANSWER by , March 11, 2012
mine does the same ,and found that the PVC VALVE is fluttering(replace it )on passenger side
ANSWER by , April 16, 2011
Ford is good, at hiding the parts that go bad. It is probably a main vacuum elbow, on the back right side or under the air plenium. There is no easy way to find the problem but it is easy to fix when found. run you hand around the area you think it is coming from, and listen for a change in the sound. you hear that and you are close, do a visual check of all rubber connectors on the hard plastic vacuum lines. If all fails get someone to do a smoke test for you it will show up in a few minutes.
COMMENT by , April 21, 2011
Thank you i will give it a try. I was thinking to try and use propane by forcing it through a small hose while motor is running at idle and when the idle speed changes i will know when im close. what do you Think? And yes i do know how to use a fire extinguisher.