My 2004 Eddie Bauer Expedition, 5.4L with EAC control began a symptom where the A/C would divert to the defrost ducts upon engine demand.

Fords have varying reasons for this problem including EAC o-ring issues. This year model has no distributer system like mentioned on other posts.

I did find a vacuum line melted from chemical or heat. The tubing is semirigid like a polyethylene style tubing with a black overwrap similar to what is used to protect electrical lines.

<a href="https://www.flickr.com/photos/twoeyedox/13804006613" title="2004 Expedition A/C blend door vacuum line 1 by Doug Cook, on Flickr"><img src="https://farm4.staticflickr.com/3792/13804006613_93930515d8.jpg" width="375" height="500" alt="2004 Expedition A/C blend door vacuum line 1"></a>

The melt point was located in the rear engine compartment, passenger side next to the battery. The line runs from the intake manifold to the firewall on the passenger side.

The fix is to find a larger piece of tubing to fit over the damaged one to act as a union. Trim back the damaged line and apply the larger tubing so the outside diameter of the original tubing fits the inside diameter of the repair piece.

The size that worked for me was labelled 7/64" (2.8mm) windshield washer/vacuum tubing. Cost = $1.20 at AutoZone.

<a href="https://www.flickr.com/photos/twoeyedox/13804006593" title="2004 Expedition A/C blend door vacuum line 2 by Doug Cook, on Flickr"><img src="https://farm3.staticflickr.com/2844/13804006593_345905dff5.jpg" width="240" height="320" alt="2004 Expedition A/C blend door vacuum line 2"></a>

 

This is a well known issue that is a result of battery corrosion eating into the vacuum line. But I must say, your pictures of the damage and repair are great.

Rep points to you for the pictures.