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Old 02-11-2011, 10:18 AM
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Unique HVAC Vent Control Issue

I just bought my first Jeep last Saturday and so far I love it....except for the few little issues I'm having. This is to be expected for a 14 year old vehicle, though, so I'm not too upset about it.

The issue I'm having with vent selection controls is that if I have my fan speed relatively high (3 or 4), and I change my selection from floor or defrost to the front facing panel vents, I get a whistling noise and no air will come from the front vents. It's almost like it does not have the power for the flaps to overcome the higher pressure created by the upper fan speeds. When I turn the fan off or to position 1, the vents will function normally and I can get it to switch over to the front panel vents and then I can turn my fan speed up to whatever I would like.

I've been searching the forum for the various vent selection related issues and had the chance to check a few of those last night. Thus far I've checked the vacuum lines under the hood, running from the intake manifold over to T under the battery and on into the passenger compartment; everything looks fine there. I also checked all of the actuation levers on the air box and non of them are broken and all vent actuators seem to be fully functioning. I also noted no obvious broken vacuum lines under there or leaks.

Common sense would say to just use the work around and change to a lower fan speed before changing vent settings, but my wife probably won't follow this procedure. I'd like to get this straightened out eventually but it's not urgent due to the current season. Any ideas would be appreciated.

Thanks so much,

Wes

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Old 02-11-2011, 11:16 AM   #2
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My Jeep has the same problem, and I've never thought of turning the fan down before changing settings. I thought I might have a small vacuum leak somewhere.

It is quite possible that it does not have the oomf to over come the air flow.

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Old 02-11-2011, 04:25 PM   #3
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yes, mine does that too. has to be below speed 2 to switch to defroster then crank it up otherwise it wont switch.
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Old 02-11-2011, 05:04 PM   #4
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The defrost is the default setting for the A/C system. So if you unplugged the vac anywhere and lost vac the vents would change back to defrost. So sometimes what happens is you have a vac leak, and will notice air always coming from the defrost. If you have a leak i am guessing that the vent doors cant provide the pressure required at high fan speed.

On mine i had a leak in the front vent actuator line. Things were all messed up, and even sometimes kind of unrepeatable. You can get a vac test set and put vac on each actuator drive line and see if you have a leak. If i had time that is what i would have done. Just unplug the hoses from the back of the controller and test from there, but i don't so i had a AC place do it. The guy had it fixed in an hour.

Let us know what ended up fixing it..
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Old 02-11-2011, 05:42 PM
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Can you perform a simple vac test by running the engine to build up vacuum and then shutting it off the see how long it stays in the system? Also, can an A/C vacuum pump be used for a vacuum test or will that pull too much vacuum?

Thanks so much,

Wes
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Old 02-11-2011, 09:12 PM   #6
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You probably can. I bet if you do have a leak, try your test, but with the engine off, switch vent settings. That way if one of them is a leaker, it will have the chance to show itself. Maybe put 30 sec or a min in each mode and see if you drop vacuum.

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