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Unread 11-25-2011, 03:46 PM   #1
digitalWJ
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97 Grand Cherokee Heat Issues?

Recently purchased a 97 Grand Cherokee that had some front end damage. I figured it would be a somewhat easy fixer-upper... and the owner did mention that there was a loose ground causing the blower to randomly cut out while driving. He also mentioned that he would have to tap the wiring under the passenger dash with his snow removal brush and the air would start blowing again.

So after driving the jeep for a week I got a little tired of the air randomly not blowing until I moved the electrical connection around under the passenger dash. I decided to take the dash apart and figure out what the issue is. I pulled the connection apart and found that the plastic connection had some burnt charred plastic around some of the connections, looked like the main ground and positive wires on either end. I pulled all the wiring out and just connected them into each other to bypass using the plastic connector they originally fed into. After doing this everything seemed to work besides the HEAT! I checked the connections to make sure they weren't loose and even checked to see if the connection at the back of the Heat/AC controls were loose... and nothing.

The only thing I can think of is that some of the wires touched which blew the HVAC fuse a couple times wiring it together... so i'm thinking that maybe a relay or blend door maybe went out after this...? Right now it's blowing luke warm air depending on the outside air Temp and the A/C does work... but no heat at all. The box is warm also which i'm guessing means the heater core is getting hot. I also noticed that when I pulled all the wires apart from the connector that I was left with a white wire that did not plug into anything on the other side of the connector, so I electrical tapped it off so it won't touch anything.... just weird that there's a wire that doesn't serve a purpose.

UPDATE: I took the jeep to a trusted local shop and they mentioned that they could not understand why I am not getting heat since the heater core is getting hot and everything appears to be wired correctly according to the wiring schematic for the ZJ. The said that they were able to ground out the white wire that went to nothing and that they were able to get only heat to come out of the vents, however that is all I am able to get.... very weird.

Anyone have any issues like this or experience with these issues?

Thanks!

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Unread 11-25-2011, 03:57 PM   #2
zachjf
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Welcome to the GC crappy heat club! Mine blows lukewarm air as well which is just plain awesome in 30degree oregon weather, Couple that with the broken heated seats and its a joy to drive my GC! Anyways, I'd start by tearing the glovebox and lower trim out and checking all the wiring first then move onto the blend door and make sure its functioning properly, seems to be a pretty large issue with the blend door motor breaking the tab off.
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Unread 11-25-2011, 06:36 PM   #3
digitalWJ
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Thanks for the info. I just don't understand how this white wire if grounded will allow for heat to work but nothing else will work... And when the white wire isn't grounded no heat comes out. I'm wondering if the white wire should be mounted to some other wire to come on when the heat is turned on from the non digital controls.
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Unread 11-25-2011, 07:59 PM   #4
KoreaZJ
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ATC or manual controls?
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Unread 11-25-2011, 08:14 PM   #5
digitalWJ
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Manual controls
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Unread 11-25-2011, 08:38 PM   #6
KoreaZJ
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what do you mean "nothing else works"?
is grounding the white wire swinging the blend door so you get hot air instead of cold?
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Unread 11-25-2011, 09:34 PM   #7
digitalWJ
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The white wire went to nothing originally. The shop explained by grounding that white wire heat would come out of the vents but thats the only temperature that will come out of the vents now. I can't get cooler air or anything else to come out other than hot air. So yes I'm guessing that by grounding that white wire the blend door is now allowing only hot air to flow through. I'm wondering if that white wire should be wired into another wire to control the blend door, but I remember from the connector that the white wire didn't go into anything originally.

Here are some pictures of the connectors before I removed them from the wiring.
photo-1-.jpg   photo-2-.jpg  
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Unread 11-26-2011, 04:37 AM   #8
KoreaZJ
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which pin location was the white wire in?
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Unread 11-26-2011, 08:41 AM   #9
digitalWJ
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I can't remember, I know it was above one of the melted pin locations and it didn't go into anything. The shop got a wiring schematic and said the same thing. I'm wondering if there is a way to look at that online to figure out what this white wire is. Unplug your connector under the glovebox and you should see that a white wire is on its own in one of the top corners.
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Unread 11-26-2011, 04:27 PM   #10
digitalWJ
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Anyone have a wiring diagram for this? I'm curious what the white wire is used for...
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Unread 11-26-2011, 05:16 PM   #11
zachjf
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I have the wiring diagram and would be glad to post the page but I already checked it and there is no plain white wire in the entire HVAC schematic, any chance you can double check to make sure its not lite grey/tan/or has a colored stripe?
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Unread 11-26-2011, 06:33 PM   #12
digitalWJ
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Just looked, it's white with a yellow stripe. Coming from the hvac control area connecting under the glove box.
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Unread 11-26-2011, 07:01 PM   #13
zachjf
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I found it but i'm afraid its not gonna be much help;

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Unread 11-26-2011, 08:24 PM   #14
digitalWJ
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Weird. Thanks for the info. I wonder why when that is grounded I get heat. I'm guessing my blend door actuator must have gone out. I wonder if I wire up a switch to that white grounded wire I can turn off heat in the summer lol
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Unread 11-26-2011, 08:57 PM   #15
zachjf
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it is really weird because, per the diagram, its an unused 5v + power supply wire and not a ground. I would tend to think you have a short in the blend door motor or the wiring to it that's causing that wire to actually activate the blend door motor. I would tear into the wiring father back up the harness, I bet you have wires that have melted together and are causing your issue as well as causing that wire actually change the heat level coming from the vents.
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