a/c blowing only through defrost - AC Auto Repair Help Forum


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a/c blowing only through defrost

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jensjeep
New User

Aug 4, 2011, 5:53 PM

Post #1 of 3 (2377 views)

a/c blowing only through defrost	Sign In

Hi, I have a 04 grand jeep cherokee laredo 4.0L. My problem is the a/c is only blowing through the defrost no matter which setting it is on. Problem started intermittently now it is consistent. I suspect a vacuum leak, but all hoses visually appear ok. Even problem areas like behind headlight and under battery tray. Then checked cruise control and found this is also out typical of vac leak. And not sure if this is related but a faint smell of butane in the cabin started shortly after the a/c settings went. The smell seems to occur when stopping with air on.

Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Aug 4, 2011, 5:59 PM

Post #2 of 3 (2367 views)

Re: a/c blowing only 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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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.

Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Aug 4, 2011, 6:18 PM

Post #3 of 3 (2360 views)

Re: a/c blowing only through defrost	Sign In

HT - having a lot of these lately? Is it a moon phase or something? And TMK most will default to defrost. Haven't run into one default to floor ducts (heat) but there's a lot of different cars out there

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