I have a 2007 F 150 4.6 supercrew. When the air is on and the truck is turned off approx 10 seconds later you hear a high pitch whistle coming from near the ac under the hood. Sounds like air releasing. Anybody know what it is and how can be fixed?

 

If you were just running your ac it's just the froen moving. If not then its possibly a vacuum leak. But thats just my 2 cents. Someone more knowledgeable will probably chime in sooner or later.

 

You're right. It's the refrigerant passing through the metering device as the system pressure equalizes.

 

Ya im a hvac tech i hear this noise all the time.