Slow HVAC controls when switching from floor vents to dash vents

Kevin Johnston

Kevin Johnston

TJ Enthusiast
Supporting Member
Joined
Sep 7, 2016
Messages
133
Location
Southwest Missouri
Search has let me down on this one. So, is it normal for a TJ to take a minute plus to switch from floor vents to dash vents or vice versa? Am I looking at a vacuum issue? Or is the baffle funked up from 15 years of awesome? Or am I just impatient and spoiled by the electronic vents in my other vehicles?

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Could be vacuum issue. If you put the fan motor on the fastest speed does it change modes faster?


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Fan speed doesn't seem to have any effect on it. I've tested it at idle and WOT going up a long hill and it's pretty consistent. I may have found an excuse to buy a vacuum test gauge.

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This happened to my old TJ, and it happens with my new TJ as well. When you turn the setting from feet to face (or anything else), it takes about 30 second to fully switch over. It's slow, and it's annoying. I too would be curious to know if anyone else has had this issue, and what the solution was.

I'm thinking maybe it's vacuum related.
 
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Bad vacuum reserve tank under the battery? I'm pretty sure there is a one way check valve before it to keep hvac leaks from causing an engine vacuum leak. Possibly the tank isn't holding vacuum so each hvac task is using current available vacuum? Just throwing out an idea that makes sense to me...
 
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Harbor freight has a hand pump you can put it inline to the intake manifold and pump with the gauge to see if it holds pressure. Does your cruise control work ?
 
Jeepaholic said:
Bad vacuum reserve tank under the battery? I'm pretty sure there is a one way check valve before it to keep hvac leaks from causing an engine vacuum leak. Possibly the tank isn't holding vacuum so each hvac task is using current available vacuum? Just throwing out an idea that makes sense to me...
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Thanks! Just went out and checked that line. I pulled the T fitting off of the check valve at the firewall and I got a long hiss (engine has been off for 3 hours). So, reserve tank is good, but I noticed that the line coming from the manifold was resting on the heater hose and has apparently gotten warm and nearly collapsed. New vacuum line tomorrow and hopefully some results!

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T Crawford said:
Harbor freight has a hand pump you can put it inline to the intake manifold and pump with the gauge to see if it holds pressure. Does your cruise control work ?
Click to expand...
I've been eyeing that pump and the gauge for a while now to check into my rough idle. I think it's time to invest now.

I don't have cruise but it's on the long list of things to add.

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Kevin Johnston said:
New line from the intake to the firewall T and the vents switch in about 5 seconds!

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Click to expand...

I'm going to have to follow your lead and check mind out as well! I suspect I may have a similar issue.
 
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