My 05 Expedition is giving me some trouble. When I turn the a/c on it blows hot air through the defrost vents no matter what I do. I used to have a thumping noise coming from the dash but that stopped. Any help with this would be great.

 

I'd guess you have two problems. The temperature problem is a broken blend door and the defrost location for the air flow is what happens when you have a vacuum leak - it is the default. The blend door is in the dash and can be fixed by removing the dash, or by using Heater Treater through the back of the glove compartment. The vacuum leak is likely in the area of the battery tray as the lines go through that area and are prone to corrosion.

 

I have never heard of heater treater. How exactly would I use that?

 

It is a metal blend door, they make versions for lots of cars. Heatertreater.com

 

I saw that on the internet. I was looking around the battery area last night and saw multiple spots in the vacuum lines that could be the issue. Do you have any idea on what size the vacuum hose is? Some spots it appears to be large tubing and other spots it is very thin. Not sure how to match that up when it goes into the "T".