I replaced the heater core...but - JeepForum.com
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post #1 of 6 Old 02-05-2018, 04:16 AM Thread Starter
WallyDog1
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I replaced the heater core...but

I replaced the heater core in my 1997 TJ 6 cyl, 5 speed. All went well with no issues except now that it's back together the vacuum that runs the flaps inside the heater box is not working correctly! The Jeep is air conditioned, no vacuum lines under the hood are damaged and vacuum is present!
Here's what's happening... The air is coming out of the defrost only no matter where the selector is put. So, if I disconnect the vacuum line to the heater box at the firewall, there is vacuum present, and plug the line back in to the heater box everything works as it should. The air diverts in all selector positions as it should till you drive it and almost immediately it get's stuck on defrost mode again!
What's the problem anyone have this happen before???
At my wits end what did I do or what broke??? Thanks!


From the Smoky Mountains of Western North Carolina
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post #2 of 6 Old 02-05-2018, 05:47 AM
TheBoogieman
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You definitely have a vacuum leak. Small leaks only show up when under load. Mine did that and I found a hairline crack where the lines go into the T at firewall from the engine compartment.

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post #3 of 6 Old 02-05-2018, 04:27 PM
Knuckelhead
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Now its a game of seek and find...
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post #4 of 6 Old 02-09-2018, 06:56 PM Thread Starter
WallyDog1
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I found the problem JUST BEFORE it was too late. So...After tearing my hair out looking for a vacuum leak I decided I had no alternative but to pull the dash and quite possibly the heater box again! I had the center dash off and the drivers lower dash off. So I was getting ready to go all the way. I had the glove box still in place still and closed. My wife needed to get her car out so I started the Jeep up and backed it out of her way. She takes for ever to get going so while I was waiting for her I opened the glove box and stared to take the strap screw out, to my dismay the center dash vent started to blow air!!!! The air deflected to all the correct outlets when the lever was moved position to position and back and forth!! I shut the glove box again and the center vent stopped working again!!!

The problem turned out to be so stupid simple! I could believe I had spent so much time looking for the problem. The vacuum lines were getting squashed between the heater box and the back of the glove box. I tucked and zip tied the lines out of the way. I've checked the operation 25 times today and it is still working.

I'm so glad my wife takes her time

From the Smoky Mountains of Western North Carolina
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post #5 of 6 Old 02-10-2018, 09:49 AM
1longcj
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I ended up with some pinched lines also, after doing my heater core. Selector wasn't working properly.
It's always nice to find a simple fix.

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post #6 of 6 Old 02-10-2018, 10:46 AM
OldJackTheJeep
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It's good to hear ritual suicide was not necessary.
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