Need Help AC blowing through defrost


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Need Help AC blowing through defrost

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lostcity
New User

Aug 14, 2011, 10:19 AM

Post #1 of 3 (2239 views)

Need Help AC blowing through defrost	Sign In

Hello all. New to this forum. I have a 2000 Excursion. I have seen post on this problem but nothing like I am facing. My AC blows through my defrost. However, if I turn the switch to high 4x4 it changes and comes through the regular vents for a little while and then goes back to defrost. I have changed the vacuum lines on the hubs but nothing has changed. This happened all at once about a week ago. I can't seem to find any vacuum leaks using brake cleaner. Is there something else I can do as I feel this is probably a vacuum issue but Im not sure where to start. Any help will be greatly appreciated. Thanks.

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(This post was edited by Tom Greenleaf on Aug 14, 2011, 1:33 PM)

Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Aug 14, 2011, 1:35 PM

Post #2 of 3 (2228 views)

Re: Need Help AC blowing through defrost	Sign In

Most vehicles the default for where air comes out will be defrost and the most common reason is a vacuum leak. Hose may be black plastic not rubber and they can partially leak or completely break and can be fixed with rubber hose.

Not sure how using 4X4 play a role in this?

T

Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Aug 14, 2011, 2:27 PM

Post #3 of 3 (2225 views)

Re: Need Help AC blowing through defrost	Sign In

The mode selection is done through a series of air doors that are operated by vacuum. When there is either a partial or total loss of vacuum, the system will default to either defrost or on some vehicles, heat. Acceleration can also have an effect on the doors for the same reason.

Look under the hood for a small black plastic hose coming through the firewall. Follow it to the vacuum source looking for any breaks, cracks or leaks. Also follow any other lines that branch off because they may go to a vacuum reservoir (storage tank) and a leak there will cause the same problem. Using a vacuum gauge to determine if you have full vacuum at any given point is the best way to find it. You can cut into the line anywhere and splice it back together with a piece of vacuum hose. Find the broken line, you found your problem.

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