Infamous Air Stuck on Deforst -
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post #1 of 7 Old 09-04-2013, 11:34 AM Thread Starter
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1996 ZJ 
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Location: Reston
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Infamous Air Stuck on Deforst

1996 Jeep GCL (ZJ)

I know...I know...I've done a search and there are tons of threads on this topic, but after watching the vent/defrost door actuator/arm in action, I've found that my problem is a little different. This is my first post here...any help would be greatly appreciated.

Anyway...the actuator arm above my gas pedal DOES move when I select air to go out vents...BUT it does not move enough to open the door. I can remove the actuator arm and open and close the door by hand, so I don't think the door's broken/stuck. I also have not found any vacuum leaks. Cruise control works fine.

Is the actuator/arm broken? I'm hoping that's the answer because a new actuator is only around $70 and with a little reaching it can be changed without removing the dash.

Any guesses?

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post #2 of 7 Old 12-06-2014, 02:56 PM Thread Starter
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1996 ZJ 
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Can anyone help with my post above from Sept of 2013, because I still have the problem.

The actuator arm above the gas pedal does move but air still will not come out of the center vents.

Am I looking at the correct actuator arm?
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post #3 of 7 Old 12-06-2014, 04:24 PM
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i think there is a blend door fix thread here somewhere. Not sure it pertains to your model year.
There is also a check valve under the hood, near the firewall on the passenger side that may need either installing or replacing on some models.

Then again, you might have a broken blend described in the thread I saw about a year ago.

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1997 ZJ, 4,0 select trac, Up country, track lok.
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post #4 of 7 Old 12-07-2014, 06:39 AM
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1998 ZJ 
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Take a mity vac and hook to the actuator, assuming we are talking about a vacuum actuator, pump it down and see if it works then. Note the reading when the door moves to the proper position. With a vac gauge you could also measure the vac at the hose that attaches to the actuator. Should be close to manifold vacuum I would think. Compare the two readings, they should be close. If the vac reading falls off quickly in the mity vac step then you have a leak in the diaphragm in the actuator. By doing this you verify that there is no leak, that the line is clear and that the control switch is functioning properly. If you move the door by hand and it moves EASILY then you have verified its not the problem. Is the air flow normal when you do this? Look at this thread for pics. Now if we are talking about ATC control thats a whole nuther can of worms.

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lol...if life is as a simple as a 5.9 making you happy, I'd say go ahead and buy it on impulse. ZJs are the way of Zen. Wax on, wax off
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post #5 of 7 Old 12-07-2014, 07:43 AM
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First rule when asking about AC issues - specify whether you have the manual vacuum-operated AC (*no* digital display on the AC control panel), or the electric ATC (*with* digital display on the control panel).

I'm guessing that since you can actually get to the vent/defrost door actuator, you've got ATC rather than the manual AC? According to the FSM, the vacuum actuator used with the manual AC can only be accessed after removing the entire HVAC box from behind the dash, whereas the electric vent/defrost motor used with the ATC can be serviced from under the steering column.

Given that the door moves when you push it manually, try and see if it's broken where it attaches to the motor. That could be a potential cause of your problem.
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post #6 of 7 Old 12-07-2014, 10:28 AM Thread Starter
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1996 ZJ 
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Thanks to all.

Some answers in regards to what was stated/asked above. First, it is not an ATC (Auto Temp Control) model. Just the 3 dials on the head unit (Fan speed, air flow direction, hot/cold). No digital display. (see below)

There is an actuator above the gas pedal that does move (see below), but does not seem to move enough to open/close the door. I have moved the lever/door by hand, but maybe it took a little more force than the actuator has strength. Bad vacuum actuator or vacuum leak if it's not strong enough to move the door?

The other actuator I can see is lower and positioned behind the VIC (Vehicle Information Center). Haven't removed enough to see if that actuator is actually moving when I switch air flow. (see below)

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post #7 of 7 Old 03-15-2017, 10:20 AM Thread Starter
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1996 ZJ 
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For anyone crawling this thread looking for the answer. This has been solved. The actuator above the gas pedal was not working. New actuator installed...FIXED!

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actuator , defrost , vacuum , vent

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