HVAC air only blowing through defrost vents

Chris

Chris

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I realized yesterday after a long drive in my TJ that the air coming out of the HVAC vents only blows out of the defrost vents, no matter where you have it set to blow from.

My first instinct is that it's a vacuum leak somewhere, but before I tackle this, I'm curious to hear from others who have had this issue, what ended up being the solution?
 
It has to be a vacuum leak since defrost is the default mode for the HVAC. I had a broken vac line along the firewall under the hood where the vac tube goes into the HVAC.
 
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Mine was this little vacuum line disconnecting, this is in the center console just next to and above the skinny pedal.

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rasband said:
Mine was this little vacuum line disconnecting, this is in the center console just next to and above the skinny pedal.

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Thanks, this is a good starting point.

When you say, "disconnecting", was it loose or something? How did you fix it? Did it just slide back on, or did you need a new connector?
 
I had a vacuum line fall off near the drivers side firewall area. It fit very loosely on so I was not sure it was right but it has not fallen off again. I probably knocked it off doing something there.
 
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Chris said:
Thanks, this is a good starting point.

When you say, "disconnecting", was it loose or something? How did you fix it? Did it just slide back on, or did you need a new connector?
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I think @Viking Jeeper covered it, they just slid back on. There’s actually 4 there, but for me only the further out ones slipped off.
 
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Mine was here on the drivers side of the engine where it popped off. I just pushed it back and was good for months then it popped of again, them i used a small zip tie

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Thanks guys! Lots of useful places to look here. I’ll check it out. Hopefully it’s easy!
 
Everyone’s gonna tell you to check for a leak etc. I had nothing. Super confused and waited months before giving up on troubleshooting and Took it into the shop, and my local Jeep guy found That the hvac line meets a plastic bushing within the dashboard wall then connects to the other line under the hood. This bushing collapsed. My guy simply carved it out of the wall and ran a direct line through. I’ll bet a case of beer that’s your problem dude. Remove your hvac control unit and check for airflow through the wall. If this is your problem- then that’s great news because it’s really a simple fix. No bad parts - just a clogged line. GL
 
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Alski said:
Everyone’s gonna tell you to check for a leak etc. I had nothing. Super confused and waited months before giving up on troubleshooting and Took it into the shop, and my local Jeep guy found That the hvac line meets a plastic bushing within the dashboard wall then connects to the other line under the hood. This bushing collapsed. My guy simply carved it out of the wall and ran a direct line through. I’ll bet a case of beer that’s your problem dude. Remove your hvac control unit and check for airflow through the wall. If this is your problem- then that’s great news because it’s really a simple fix. No bad parts - just a clogged line. GL
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Great advice! I have to put in a new stereo head unit, so I'll be in there anyways, in which case I'll check out the lines.

Thanks for this!
 
Mine does that every now and then. I found that if I turn the fan on full speed, then cycle the select switch all the way to the front defrost and then back to the AC setting it will start blowing through the front vents. I should probably look into that some day lol
 
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I had a vacuum line wear through in the engine bay, under the battery tray. Being a small hole getting larger, it gradually got so the air would move from the floor to the defrost during low vacuum periods when I climbed long grades.
 
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I have a similar problem, when I am driving up big hills in 5th or 4th i really need to put my foot in it (3:73s,33s, 5spd sucks!) and the more gas i give it, air slowly starts coming more and more out of the defroster when I have it set to my body.
 
Check at the firewall where the heater hoses connect. Just above them is the vacuum line that goes through the firewall with a check valve. It is a pretty tight bend on the plastic vacuum line. Mine had a crack/split in the line that was next to impossible to see until I disconnected it and straightened it out. I ended up cutting the line and slipping a small piece of rubber vacuum tube over it to fix the problem.
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