Heat/AC vent problems

[bjorklunddaniel]

I have an 03 expo and my vents are stuck in the defrost position. It stays in the defrost position no matter what the position, temperature or blower setting. Could this be a vacuum hose problem?

[phantom_smack]

Have you changed the battery?The source vacuum line runs right next to the battery box and the corrosion build up on the cable sometimes migrates to the vacuum line weakening it and when you change the battery the vacuum line cracks in two.

[bjorklunddaniel]

Yes, I replaced the battery about 4 months ago.

[phantom_smack]

Its a black plastic vacuum line,if you dont see it start the vehicle and listen for the hiss.

[TBIRD430]

There is also a vaccum check valve that can go bad on this same black vaccum line. It is found up by the firewall, and is usually a blue or green plastic 3-way valve.

[donbunch]

My AC works fine for the most part, except when accelerating or going up hills it blows out the defrost vents. I have checked all the vacuum hoses by the battery and have repaired them, also checked under the battery (took it completely out as well as the tray).

What is the thing behind the battery where the vac hoses go, it is a black box of some sort which slides into the tray that holds the battery. The vacuum lines going to it were good, just wondering what this thing is. (found the answer - it is the vacuum resovoir - mine was fine)

I do have a hiss which seems it is coming from the AC accumulator/drier which I can hear for about 30 seconds after I turn off the engine. Could this hiss be the issue with my AC blowing out the defrost vents?

[TBIRD430]

Yes sir. =o)