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Unread 07-07-2011, 12:45 PM   #1
TontoKowalski
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A/C will only blow through defrost vents

What Happened?!?

I turned on my A/C the other day and for some reason on every setting, it only blows up on my windshield...as if it's going to defrost it.

When you select any other vent, floor, etc setting it keeps it pointed straight to the windshield.

Is there any way I blew a fuse or something or an arm is stuck somewhere?

It's a 1996 Jeep Grand Cherokee Laredo, V8.

Thanks,
Tonto

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Unread 07-07-2011, 01:02 PM   #2
MaintMech
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If the air is still cold you have a vacuum leak. Jeeps default to defrost if there's a vacuum leak. Check the "T" fitting by the firewall first, then all of the vacuum hoses.
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Unread 07-07-2011, 02:02 PM   #3
doomi
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+1 to it being most likely vac lines. Same thing happened to me and it ended up being the vac line coming from the bottom of the battery tray.
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Unread 07-07-2011, 09:35 PM   #4
CrzyMtnMan
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+1 on this, the way they do the HVAC controls I dread the day I have to work on this. Everytime I change the air direction the nightmare of helping a firend with this years ago goes through my head. Easy system once you learn it, but the learning curve messed with me trying to diagnose the dang thing. I keep a special stick on reserve for the engineers that decided to use vacuum to control HVAC controls.
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Unread 07-08-2011, 01:09 PM   #5
TontoKowalski
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What am I looking at if I have a pro fix this? I'm thinking this might eclipse my mechanical skills...
I've got no clue what a vacuum hose looks like and wouldn't have the foggiest idea of where to begin.

If I could locate this "T" fitting, what would I look for? An actual crack or leak?

Dumb question, (get ready): If it's leaking, would it be leaking cold air? Fluid? Magical pixie dust?

Thanks,
Tonto
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Unread 08-28-2011, 11:33 AM   #6
TontoKowalski
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I was checking around looking for a fix with the TValve and I snapped one of the mini vacuum hoses coming from the firewall.

HOW ON EARTH am I going to replace this? It's as thin as a coffee straw. It looks like it's impossible to get to b/c it's surrounded by bigger cables and is a really tight area.
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Unread 08-28-2011, 12:46 PM   #7
morrigon
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[QUOTE=TontoKowalski;12089312]I was checking around looking for a fix with the TValve and I snapped one of the mini vacuum hoses coming from the firewall.

HOW ON EARTH am I going to replace this? It's as thin as a coffee straw. It looks like it's impossible to get to b/c it's surrounded by bigger cables and is a really tight area.[/QUOTE

The Advanced stores here in Colorado carry the vacuum lines and the little Tís and junctions your looking for. The few stores I been here are all in the same spot Ö near the motor oil on a rotating rack next to the oil plugs. Any auto parts should have these not just Advance.

You can get them in all shapes and sizes. In most cases you buy a verity pack and may only use a few of the pack itself. Vacuum lines are fairly simple to understand. Your engine makes vacuum and the vacuum is used to run some devises on your jeep. You just donít want any leaks in any of the lines. Hoses that are cracked need to be replaced and plastic Tís and such need to be replaced if brittle and break easy. If there is a one-way valve I would just replace them at the same time. You could buy and replace the full lines and fittings from start to finish for less then $20 I would think. They donít cost much. Hard part is finding them and then getting to them in some spots.

If it was me I would just re-do all the lines because if you have one leak more are close behind but you can just follow the line and do a quick fix on the leaks you see right now. Just run your fingers lightly over hoses to feel the suction in bad spots and a lot of times you can hear the suction its making witch makes it easy to find.

The Tís and the connectors may not look the same as what you take out but as long as they are the same size and fit snugly into the vacuum hose you can use whatever works as long as it holds the vacuum. Get some tie straps and tie strap them out of the way so they donít hit hot spots like exhaust or what not or rub against things and slowly wear holes in them.

Hope that helps?

AJ
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Unread 03-18-2012, 06:22 PM   #8
kenneth58714
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Me too..

I have the same issue. I figured it would be a vacuum issue.

Quick Question- Could this also be the culprit behind my engine revving at idle for no reason?
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Unread 06-24-2013, 07:50 AM   #9
TontoKowalski
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So, I had a mechanic fix this for me about a year ago...and now it's back. And, I'm driving to work in the DC humidity and sweating my beezos off on the 45 minute drive!

To find this suspect vacuum hose, I have to remove the battery and look for a 1/4" hose that's hidden underneath?

Also, can somebody explain what a vacuum system is? I mean, I assume that it uses air pressure to move a flap in and out that directs the air...anybody know where this flap is? Is it accessible?

Thanks,
JT
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Unread 06-24-2013, 07:57 AM   #10
dellis
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Vacuum leaks aren't hard to find, and your problem is common. If you want help, I'm in Falls Church and always willing to help out a fellow jeeper ... mostly daytime hours or Wed evening. I can show you how to test your vacuum with a gauge, show you the vacuum lines, show you how to test for a vacuum leak, and who knows? We might even find your problem.

You CAN NOT drive around DC without A/C. :P
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Unread 06-25-2013, 12:38 PM   #11
TontoKowalski
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Quote:
Originally Posted by dellis View Post
Vacuum leaks aren't hard to find, and your problem is common. If you want help, I'm in Falls Church and always willing to help out a fellow jeeper ... mostly daytime hours or Wed evening. I can show you how to test your vacuum with a gauge, show you the vacuum lines, show you how to test for a vacuum leak, and who knows? We might even find your problem.

You CAN NOT drive around DC without A/C. :P
Hey dellis, thanks for the offer...but I've got to pass. It's so balmy and hot here that it may need an immediate cure. So, I've got a local mechanic by my office that is going to take a look for me.

($95 diagnostic and he might take it off of labor depending on what it needs when he's done)

Do you ever go trail riding in the NOVA area? I've got a buddy with a Wrangler who both of us are looking for places to get some dirt on our tires without driving 3+ hours to get to.
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Unread 06-25-2013, 01:46 PM   #12
carrasaurus
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So I have a very similar problem - and I live in Northern VA , Loudoun County - but my AC goes to the defrost vent only as I'm accelerating. Vacuum line also?
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Unread 06-25-2013, 02:19 PM   #13
Uniblurb
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Yep, especially since you have the Laredo which should be manual HVAC controls, and I also have a 96 4.0.

Start at the drivers side of the intake where the main vacuum line attaches. Then follow it across the firewall towards the passenger side and you'll see a "T" where the small black plastic line goes through the firewall next to one of the evaporator tubes and this goes into your HVAC control. If you continue to follow the main line past the "T" on the firewall it will make a front turn and is right on the inside of the fender. From there it's connected to the to the speed control servo (cruise control) with another "T" then follows fender where it eventually goes under the battery tray where it's connected to the bottom of the battery box, which is a vacuum reservoir, by a rubber hose which tends to rot/come off. Inspect this whole line for breaks in it or bad hose connections. Also make sure the battery tray is not cracked on the sides/bottom which will also cause the controls to go to default defrost.

If you can't find any vacuum leaks in the engine compartment listen for them inside the dash with the engine running, the control turned on, and the fan off. I've actually repaired the small broken lines behind the dash with the empty ink tube out of a bic-type pen, cut the broken part out of the line, slightly heat the ends of the lines, shove about a 3/4" piece of empty ink tube in, then use good electrical tape on it. Leak has never surfaced again and control works fine. It should also be noted sometime those controls go bad. Good luck.
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Unread 06-26-2013, 07:58 AM   #14
TontoKowalski
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Success!

You guys were right, it was in a vacuum line...

I got home last night and decided to try and fine this line that goes up under my batter, who designed that btw?

I found it, took the battery and tray out inspected the line and the box that it goes into, didn't see any abnormal wear and tear. I did happen to have extra hose laying around so I just replaced that section...what is that box btw?

So then I followed it back to the firewall. Where the hose T's off, there is a thin hose that shoots up into the firewall. Somehow, somewhere that tiny hose snapped.

Now, from the T, the tiny hose fit into a thicker outer hose. So I removed that hose and noticed that the firewall part of the hose broke off inside of the larger housing hose. I tweezed that piece out...struggled to get my fat hands back there against the burning engine block, etc...and inserted the tiny tube into the larger tube.

I was 100% skeptical that it would work. I put the key in, turned it on and in about 5 or 10 seconds the thing started pumping out of the dash vents.

Eureka! Now...anybody got any tips on re-juicing my AC system so it's like a meat locker when I drive?

Thanks for the advice fellas, worked out fine...
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Unread 06-26-2013, 08:38 AM   #15
dellis
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Quote:
Originally Posted by TontoKowalski View Post
Do you ever go trail riding in the NOVA area? I've got a buddy with a Wrangler who both of us are looking for places to get some dirt on our tires without driving 3+ hours to get to.
Nah, I've got too many kids that suck all the life out of me.


(But I love them).


*Glad you solved the problem!
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