Hello everyone. I finally got my 01 5.4 EXTCAB and I start noticing some weird stuff. The AC sops venting to the front panels and vents out to the windshield during semi to hard acceleration then it goes back to the front panels after I let off the gas or the engine is not pulling as hard . Any ideas on what this could be?

 

probably a leak somewhere in your vacuum lines.

 

I'll buy the manual so I can trouble shoot the vacuum lines.

 

I have a haynes manual for f150s / explorers. I can take a look if there is a vacuum line diagram and scan it for you if you'd like.

I'll take a look and see if it's even in there.

 

Thanks for the offer. I just bought the manual, I don't think its the vacuum but I'll give it a go. It's probably the manifold that controls the flow of air under the dash.

 

The flow of air is controlled by vacuum controlled motors and with a vacuum leak air flow defaults to the defrost. That's why it is a vacuum leak somewhere either under the dash or under the hood.

It'll be a small vacuum leak. The reason it only happens under a load is because as the throttle plate opens wider vacuum gets weaker and weaker, so with the throttle plate closed vacuum is the highest and it is strong enough to allow the vacuum motors to work correctly, but when you hit the gas the vacuum decreases and isn't strong enough to hold the vacuum motors that control air flow.

 

Thanks for elaborating on this issue.