08 4.6 v8 hissing from passenger side upon acceleration.

[abe21]

Upon the first few seconds of acceleration I get a hissing noise from under the passenger side glove box. Also, the air flow through passenger side vents is very weak compared to the drivers side, the dual control does not seem to work for the passenger side, and AC only blows through drivers side. Some say its a blend door issue, but im thinking some sort of a vacuum leak. Thoughts?

 

[swshawaii]

Search results for query: yg360

www.explorerforum.com

 

[94Eddie]

The problem might be the check valve that keeps the vacuum reservoir under vacuum during engine acceleration. During acceleration the engine does not create a vacuum. The vacuum reservoir is there to ensure the climate controls still function when this occurs. The check valve stops the reservoir from losing its vacuum when the engine is no longer making a vacuum. When the reservoir loses vacuum it make a hissing noise and it is located behind/under the glove box. The valve is located in the engine bay on the passenger side near the firewall. You can remove it and blow through it and if you can blow through it from both ends then it has failed. I had this fail a few years ago and it was simple to replace and the part costs $10 off of Amazon. The link to the part is below.

Ford XR3Z-19A563-AA Air Conditioner Control Valve