ZJ Defroster always on... - JeepForum.com
 
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post #1 of 3 Old 09-14-2012, 06:14 PM Thread Starter
1SASjeepster
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1992 YJ Wrangler 
 
Join Date: Apr 2010
Posts: 726
ZJ Defroster always on...

Hey, just wanted to tell you guys what I experienced and what fixed it. My wife has a 1998 Grand Cherokee with a 5.2 HO V8. About a year ago, when ever she would give it gas on the highway (ex: passing a car), the air condition would stop coming through the vents and switch to the defroster. As soon as she would let up on the gas, it would switch back to the normal vents. I couldn't figure this out for anything. We just learned to live with it. Then, it got worse. All of a sudden it only blew air out of the defroster. (On a side note, my blower/fan speed switch sometimes didn't work in high speed... so I needed to check that out also.)

I began to check out the blower switch problem so I removed the "heater air condition panel switch" in the center instrument panel. I carefully removed the three plugs just so I could remove the panel and check it out in more detail. I was hoping to be able to open it up and repair the blower speed switch. Once the panel was out, I realized it couldn't be repaired... at least, not by me. So what to do now? Hmmm, those are some mighty interesting colored vacuum lines coming off of that "door selector switch" for the venting system. I wonder where they go? I started to trace them... that got about six inches tops. I then broke open the factory manual and boy, was that a big help.

I was looking for the "vacuum tap" (their name, not mine) that ran off of the intake manifold and feeds this switch... but they didn't bother saying where the damn thing is. Usually they are very good at narrowing down its location, but not today. So there I am looking at the intake manifold in all its glory and looking for any vacuum lines coming off of it. Then I found it or at least, I found a vacuum line that appeared to be going through the firewall.

It comes off of the rear of the manifold and goes to the passenger side of the engine compartment right above the ECU (computer), near the radiator overflow bottle. There is a "T" vacuum junction and there was my problem. The plastic vacuum line broke off. Apparently it was cracked and then finally snapped. I cleaned up the connecting hose by removing the broken plastic tube and then reconnected it. My venting system worked perfectly now. It would switch unlike ever before BUT there was a problem now. And please be aware of this, so it doesn't happen to you.

WHEN YOU REMOVE THE MIDDLE PLUG IN THE HEATER CONTROL PANEL (THE SELECTOR SWITCH FOR THE VENT) BE CAREFUL. THIS PANEL HAS A SMALL SPRING WITH A "BB" SITTING ON TOP OF IT. AS SOON AS YOU PULL THE PLUG, IT GOES WHEREVER IT WANTS TO. SO I LOST THE BB AND TRIED TO REPLACE IT WITH ANOTHER BB BUT COULDN'T GET IT TO WORK. JUST WARNING YOU. BE "BB CAREFUL". THE BB WAS CLOSE TO BEING THE RIGHT SIZE, BUT I HAD PROBLEMS WITH THE SWITCH AFTER THE NEW BB.

I hope this helps out someone with this problem.

Take care,


Check out "YJ V6 Conversion" if you want to see a frame up restoration of my 1992 YJ.

Check out "WWII Jeep Photos AND Restoration of..." if you want to see the original JEEP in action...

Last edited by 1SASjeepster; 09-15-2012 at 05:47 AM. Reason: spelling error
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post #2 of 3 Old 09-15-2012, 05:30 AM
KoreaZJ
Registered User
1994 ZJ 
 
Join Date: Aug 2011
Location: GANGNAM STYLE
Posts: 2,665
Vacuum lines are not normally disconnected from the rear of the control panel.

Follow those "mighty interesting colored vacuum lines" further down behind the right end of the VIC and you'll find the quick disconnect. Push it out to the right as shown for easy access. Disconnect, then remove the panel.




For your intermittent Hi-Speed Fan problem... check the connectors mounted to the front of the heater housing for pin damage from overheating.

The burnt pin in the corner is GROUND.
The burnt pin next to the opposite corner is power for Hi-Speed Fan only.



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post #3 of 3 Old 09-15-2012, 05:44 AM Thread Starter
1SASjeepster
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1992 YJ Wrangler 
 
Join Date: Apr 2010
Posts: 726
KoreaZJ,

I can't thank you enough!! Your experience and insight will help me out a bunch. As you figured out, I didn't remove the VIC panel yet, but now I will. Thanks again! Have a great weekend!

Take care,

Check out "YJ V6 Conversion" if you want to see a frame up restoration of my 1992 YJ.

Check out "WWII Jeep Photos AND Restoration of..." if you want to see the original JEEP in action...
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