99 Wrangler Sport (non AC) Air flow vent not working. - Jeep Wrangler Forum

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Old 01-06-2006, 11:37 AM
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Unhappy 99 Wrangler Sport (non AC) Air flow vent not working.

Need a little help here... and yes, I'm a newbie. I have a 99 Wrangler Sport and the air control knob no longer seems to be working. I have air coming out, but I can no longer change between heating the floor, heating the drivers, or changing it to defrost. I'm talking about the knob on the far right of the pannel. Seems easy enough to reach through the glove box compartment but I don't know what I'm looking at.

Please help me stop my baby from fogging up!!!
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Old 01-06-2006, 12:11 PM   #2
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Most of the time when the TJ HVAC plenum box stops routing air it's because of a vacuum leak. Open the hood and look on the intake manifold - you will see a small hose coming off of it that goes across the firewall to the passenger side. There it Tees into two routes - one going to a vacuum reservoir located below the battery, and one going through the firewall and to the selector knob you see. Inspect the hose - and experiment with blocking off the vacuum reservoir to see if the problem is before the knob, or the knob itself. You may also want to stick a vacuum gauge on there and see where it's registering. It should be around -15psi or so (normal engine vacuum), and when you rev or stop the engine (eliminating vacuum) it should stay there as there is a check valve that should keep the vacuum in (or the pressure out depending on how you look at it) and the vacuum reservoir should last a good while unless there is a leak.

//1998 Jeep TJ {'4\"', 'TFLX LAT', 'AA HD SYE', 'HF 8000Lb', 'LockRight', 'Armor', 'Body mods', 'Misc Mods' = 'true' };
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Old 01-06-2006, 03:05 PM
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Thanks, I'll check that out. I think I may have pulled something while connecting a Sirius antenna. I had the glove box off and was reaching through there to pull the wire through. The knob turns but doens't feel like it's clicking or doing anything. I seem to remember some resistence when it changed from feet to body to defrost.... maybe I'm not explaining this well.
Just keep in mind air still comes out and I control how much and the temp.. I just can't switch between the different directions of the flow.
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Old 01-06-2006, 04:15 PM   #4
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If your knob just freely turns and nothing happens then the knobs could be stripped out on the inside. I had this happen to mine, the plastic insert on the back of two of the knobs had broken. I think 3 new knobs at the dealer was 20 bucks.
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Old 01-07-2006, 07:07 PM   #5
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Another common problem for the TJ is a broken or stripped blend door. If the blower blows but does not switch to defrost look under the drivers side dash above and to the right of the skinny pedal. Have someone move the blend switch from vent to defrost and watch to see if all the vacuum pull offs are working properly and if the blend doors are actaully moving. HTH
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