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Old 01-22-2014, 10:01 AM   #1
Join Date: Aug 2013
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heating advice

Hey, have a heat issue... Been putting off getting out there and finding a solution but on a -6 degree drive in this morning, it had me thinking on it.. lol. I am not sure what is going on.. I have some ideas, but not sure where to start looking.. The symptoms are as follows:

I have heat.. It keeps up on a cold day somewhat.. But on a real cold day it struggles.

The vent door does not open or close by using the slider lever. It stays in the open position.

With the heat on, if you manually close said vent, the airflow stops and nothing comes out the window vents. As if in heat mode it is sucking air from the cab thru the passenger floor vent thru the heater core. And the right cowl vent is not opening.

No air comes out the passenger floor vent except when in the off position. Nothing in heat or vent position.

It seems I get air flow out the defrost vent and driver floor vent, no matter what the selector is on.

Any ideas on where to start messing with things. Not sure where exactly everything is located inside. I guess most things are behind the dash. I did take the dash apart shortly after I bought it in the summer to change a few bulbs and everything seemed to be working and hooked up, other than the vent opening and closing on the passenger side.

Any advice or help would be great..
Thanks ahead of time.
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Old 01-22-2014, 10:27 AM   #2
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The vent doors are actually at the bottom of the heater housing. They are cable driven, one open and closes the passenger side vent at the far right side, the other opens the heat flap at the center of the floor hump. There are a couple of vacuum flaps in the cowel also, but it'd useally the floor vent cables that slip off the retainers.

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Old 01-22-2014, 05:03 PM   #3
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Also forgot to mention.. I think my left cowl is opening most the time and not the right.. I get cold air coming down from the steering wheel.. I guess the vent up in the dash is allowing the child's air in since the cowl is staying open maybe?
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Old 01-22-2014, 05:34 PM   #4
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Check out this sweet thread I found earlier: YJ Heating System Explained

Might help explain your situation.
1995 - 2.5L Low Output Wrongler
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Old 01-23-2014, 08:01 AM   #5
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Yeah I have read that thread a bunch before posting.. mine doesn't seem to follow the directions described in that thread.. like when the system is off that's when I get air thru the passenger vent, when it should be closed.. could my vacuum hoses be criss crossed for the cowl doors?
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Old 01-24-2014, 11:10 AM   #6
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As a test, this morning I wedged the vent door closed and turned the selector on the heater to off. I had warm air flowing out the defroster vents. Almost as much air as when the blower is on. But I did not have the other cold air coming in from the steering wheel. It had stopped. So the cab was pretty much sealed off from the outside air, other than that coming thru the right cowl vent and thru the heater core.. Now in the off position like I had it, everything should of been closed. But it acted as if it was in the heat selector mode. My vacuum lines are obviously working, just not how they are supposed to... Could it be they are on the wrong plugs, like hooked up backwards? Would this explain the opposite workings?
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Old 01-25-2014, 07:38 PM   #7
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Just an update.. went out to play with the dash here today... got everything taken apart and got to the heater controls to see what was up.. everything was hooked up. BUT, the vacuum control switch lines were switched.. there are three posts and two vacuum lines attached.. green should be in the middle and the black should be on the side closest to the switch/ passenger side.. my black was on the drivers side post which should be the empty one.. switched it to the other post and the passenger side cowl gate ifs working as expected...

My vent door it's still not opening or closing... I have narrowed that down to the wire from the controls to the drivers cowl gate, which then runs to the passenger floor vent... I think the cable between the cowl gates are connected and working.. my test driving Friday with the vent door manually shut, seemed to also close the drivers cowl... I need to check the cable connection at the drivers cowl and see what is going on there.. I ran out of light before I could check that..

Is the drivers cowl gate connector accessible from the cowl on the hood? I'm assuming if I take the vent off I can access the connection??
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Old 01-25-2014, 10:13 PM   #8
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No...the driver's side cowl gate is accessible only from a very small contortionist that can lay on the floor in between the seats and rest his head on the brake pedal while he reaches up under the dash to work on it...lol. But I heard that his hourly rate is extreme this time of year, although if you can wait until March 17th you can probably get a little green dude to help you out!

The driver's side cowl gate is inside the Jeep. If you take the grill off of the cowl, you get to see a black plastic box. That's it. Your cowl gate is about straight up from your gas pedal, about 3-4" down from the top of your dash. Not a fun place to be, and even worse if you need 2 hands in there to do something.

Its a lot of work, but the easiest way to get to it is to take the dash out, at least the drivers side and the center dash. And all the gauges too. Then you can see right in there...like I said, it's a lot of work.
'87 YJ, 4.2L built and bored, 8" of lift, 8.8 rear, AX15/NP 231J, Tom Woods drive shafts, Flat fenders, 12,000LB winch, Custom bumpers, Rattle can paint job. Never completed...
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Old 03-03-2014, 11:55 PM   #9
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Hey what's up everyone I am having a similar problem with my 89 yj I have heat when the truck is idle but once I get going freezing air comes through I had changed the thermostat earlier in the year it seems like a vent is open any ideas?!

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