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Old 08-17-2007, 01:00 AM   #1
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heater not switching to defog

my defroster wont blow any air,i noticed at 20mph i here a flap in the heater box close and when i turn a corner it seems to open but still no air to defog vents,the control still activates the floor and mini vents for the side windows but no air to the upper vents flowing to driver and pass. i just bought a haines manual but it doesnt cover this in depth any ideas thanx tbone ps this is a 97 wrangler with a 4 banger

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Old 08-17-2007, 05:50 PM   #2
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I have an '05 - has vacuum actuated vent controls. Do you maybe have a vacuum line off under the hood?

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Old 08-17-2007, 05:51 PM   #3
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I had the same problem earlier this year and a disconnected vacuum line was the culprit.
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Old 08-17-2007, 06:00 PM   #4
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x2, my mechanic fixed when i went for an oil change.
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Old 08-19-2007, 05:18 PM   #5
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If you put it in defrost and the fan is on low, then when you turn the fan higher you hear a door slam in the dash it's a small pin in the heater box itself. The heater box needs to come out to replace it, it's like a $5 part. Mine does the same thing on both my 97's.
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Old 09-06-2007, 06:09 PM   #6
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If you put it in defrost and the fan is on low, then when you turn the fan higher you hear a door slam in the dash it's a small pin in the heater box itself. The heater box needs to come out to replace it, it's like a $5 part. Mine does the same thing on both my 97's.
Mine does the same thing. Is it hard to remove the heater box. And, after you remove the heater box, is it hard to find the pin, etc. Does the pin have to be purchased from a Jeep Dealer?:
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Old 09-06-2007, 11:26 PM   #7
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vac line

your heat/air switch is controled by vac. if you look on driver side on top of plentem right behind throttle body there is a small vac line that runs from the passenger side and should have a rubber 90 on it that plugs into the top of the intake i'd check it first. mine came lose behimd the glove box where that small black vac line splits into the 4 colorrd ones and let me tell you it was a pain to connect it back. i took out the glove box and theres a small tunnel and found the problem with a flash light and got lucky to get it reconnected good luck
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Old 09-07-2007, 02:27 AM   #8
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I was having a problem with my a/c. On max and on the highway it would switch to defrost. I found the problem it was the vacuum check valve. they look like little tops in the vaccum line it has two. they are a one way valve for vaccum..
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Old 09-12-2007, 07:40 PM   #9
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I was having a problem with my a/c. On max and on the highway it would switch to defrost. I found the problem it was the vacuum check valve. they look like little tops in the vaccum line it has two. they are a one way valve for vaccum..
One more question about my defrost problem...I have plenty of air blowing from the "heat" position in the floor, plenty when going to the vents, but no air regardless of anything going from the defrost vents to the windshield. Changing the fan speed does nothing. When I start going through the gears, around 2nd gear or so, I hear, what seems like a door shut or ?... but nothing happens to blow air from the defrost vents! From eveything I can see under the hood, the vacuum lines seem to be fastened, etc. I willing to tear it apart, but don't want to waste a lot of time if I can get some pointers? Thanks! genemarsh
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Old 08-08-2008, 11:45 AM   #10
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Bringing this up again, I removed my center cover, glove box and the drivers side kick panel and knee blocker. Played with the heater controls and found the defrost vent vacum motor is broken inside the heater box. With no blown up picture of the inside of the heater box showing the doors themselves it looks like that little piece of plastic that connects the two are broken, while the vacum motor works it does not DO anything but turn the broken arm.
Any suggestions on how to fix this without pulling the whole dash to get the heater box out ? $#$# Jeep, between their evaporators and this crap it almost seems intentional that they use the heater box as a source of income for the dealers, giving engineers the benefit of the doubt, I'd like to meet the accountant that designed this and let HIM fix the dam thing..
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Old 08-08-2008, 02:20 PM   #11
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Fixed for now, I used a phillips headed self tapping screw and put it thru the part that was broken off, screwed it thru the hole that is in there and continued turning it till it was loose enough to turn easily. Then put it in the hole in the heater box it is supposed to go into [or come out of] and screwed it into the heater door and got it nice an tight after experimenting with the correct angle so it's closed, open. Tightened it down. Then unsnapped the vacum motor, it pulls straight out, looped the end of the nub on the arm and snapped it back in, whoo hooo, got defrosters again as well as mix, at least for now. I was tempted to put some jbweld on the threads but now that it's in I'm leaving it alone. There was about 1/2 inch of thread sticking out that went into the defroster door. Thats a tight work area. If it comes out again I will do the jbweld and see how that holds.

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