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Unread 03-24-2008, 10:55 AM   #1
mdplayer
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Join Date: Feb 2006
Location: North Conway, NH
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Any thoughts on my defroster problem??

Recently, I have been having a problem with my front defroster and it is baffling to me. Here the problem:

When I turn on the jeep and get it going, I turn on the defroster and nothing comes out. The fan is blowing but no air is coming out of the defroster. When I turn it to high, it sounds as if it is blocked or something like that. So to warm up, I just turn on the vents or something and everything works perfectly. I keep trying to switch back and forth to see if the defroster will work. Eventually, and I am not sure if it has to do with warming up or whatever (I haven't timed it or compared with different temps), but it sounds like the "blockage", for a lack of better words, gets pushed through or bypassed or whatever, and warm air comes through just fine and everything works as it should. If I would turn off the car and start it back up when everything is working, the whole cycle starts over again.

I haven't noticed anything coming out of the vent when all is working properly and I haven't noticed a certain amount of time or temp that is needed to get the air coming through. The jeep is up for inspection in April and I could certainly have them look it over, but thought if I can save some bucks by not having them do it, I would rather do that.

Any thoughts or has this happened to anyone else??

Thanks in advance....

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Unread 03-24-2008, 11:02 AM   #2
grinwa
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1999 TJ Wrangler 
 
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Location: Port Orchard, WA
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Check all the vacuum lines from the engine to the switch. One might have crack or leaking. There is a vacuum reservoir in the passenger side fender, too. Also check your switch and the lines coming out of there.
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Unread 03-24-2008, 11:10 AM   #3
LARSONEM
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1997 TJ Wrangler 
 
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Sounds like you have a vacuum problem. Insufficient vacuum is not allowing one of the panel doors in the heater box to open quickly. Beside the radio, looking up from the drivers footwell, there are three vacuum actuators. As you move the lever from floor (heat) to panel (A/C or Vent) to defrost, those actuators will open and close doors in the heater box to direct the airflow to the proper location. The vacuum is supplied off the intake manifold and passes through the firewall near the heater core. Sounds like the defrost eventually works after it builds enough vacuum to fully open the defrost door in the heater box.
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1997 Red Wrangler 4.0L - 5 speed - soft top w/full frame doors - 2 inch spring spacers and 1 inch body lift - 31 x 10.50 BFG on 15 x 8 Pro Comp 8069 rims
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Unread 03-24-2008, 12:36 PM   #4
mdplayer
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Hrm, interesting..is what something that a moron (myself) can replace and would something like that be costly??
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Unread 03-24-2008, 02:33 PM   #5
jgorm
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I found a leak under the battery on that vacuum tank thing. The hose was cracked. But mine would only come from the defrost no matter where i set the thing at.
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Unread 03-24-2008, 02:37 PM   #6
daveg13
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Before you start getting too deep, start with the simple things, pull your selector knob off and make sure it's not broken. Sucks when you tear the whole dash apart and find out that's the problem. Don't ask how I know.
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Unread 03-24-2008, 07:06 PM   #7
LARSONEM
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I could be costly. I've got to figure that you have a vacuum leak, since your defrosters eventually work. All of the vacuum lines are color coded going to the actuators. There is a plug on the right side of the radio I believe, where all of the vacuum lines connect (plug together). Make sure that is tight. The line colors are as follows:

Yellow - Defrost actuator (mid position)
Brown - Floor actuator
Blue - Defrost actuator (full position)
Black - Vacuum suppy (from reservoir)
Red - Recirculation actuator

You should be able to get to this connector after removing the glove box. Also this connects to the back of the HVAC control panel which means you have to pull the center of the instrument panel out that covers the radio.
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Unread 03-25-2008, 10:27 AM   #8
mdplayer
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Quote:
Originally Posted by daveg13 View Post
Before you start getting too deep, start with the simple things, pull your selector knob off and make sure it's not broken. Sucks when you tear the whole dash apart and find out that's the problem. Don't ask how I know.
Definately not the the knob as it works eventually, without me changing anything....so seems like it could be a vacuum issue..

I do agree...would suck to pull everything apart and have it something simple like that.
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Unread 03-25-2008, 10:28 AM   #9
mdplayer
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Quote:
Originally Posted by LARSONEM View Post
I could be costly. I've got to figure that you have a vacuum leak, since your defrosters eventually work. All of the vacuum lines are color coded going to the actuators. There is a plug on the right side of the radio I believe, where all of the vacuum lines connect (plug together). Make sure that is tight. The line colors are as follows:

Yellow - Defrost actuator (mid position)
Brown - Floor actuator
Blue - Defrost actuator (full position)
Black - Vacuum suppy (from reservoir)
Red - Recirculation actuator

You should be able to get to this connector after removing the glove box. Also this connects to the back of the HVAC control panel which means you have to pull the center of the instrument panel out that covers the radio.
Thanks for all the info. Seems like I have a little weekend project on my hands...
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Unread 03-25-2008, 10:35 AM   #10
jgorm
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Go buy a cheap vacuum gauge (~$10-20). It will really help you find the problem. I had 20" at the manifold, but only 4" at the fitting that goes into the cab.
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Unread 04-01-2008, 12:09 PM   #11
mdplayer
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One more question

I didn't quite get to it this weekend, but some new info has risen about it that might help pinpoint the problem, although it seems as if it is the vacuum problem.

When it is warmer, say 40 degrees and warmer, the defroster kicks right on, no waiting. Will the outside air temp have some effect on the vacuum issue??

Thanks
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Unread 04-01-2008, 05:22 PM   #12
Maverick14
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1997 TJ Wrangler 
 
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I have a 97 TJ and my front defroster started doing some of the things yours was doing until eventually the lever that rotates and moves the lever broke off. So know i have mine cracked open with a rubber hose. It sucks.
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