well its starting to wharm up here in the great state of california, after we had teaps of 100 last week i decided to kick on the AC and go for a drive. well since i hardly used the heater since spring began last november, i didn't notice this. with the AC fan on high and i accelerate, the vents will shift from the front vents to the defrost vents and when i level out i got the defrost and main vents, and when i brake, it goes full on main vents.. i hit up the search but i couldn't get the right combo of words to hit any results. could this be some funky vacuum issue? im stumped..

 

Any time you see your airflow being redirected depending on engine speed, it is related to vacuum leaks.

Somewhere you have a leak. The most likely places are the spherical vacuum canister behind the front bumper is cracked, or one of the underhood vacuum lines is leaking. These are the ones subject to heat, vibration, and chemicals, and will usually fail before anything under the dash will.

It can be maddening tracking it down. Usually, I recommend just replacing them all, since if you have one cracked and leaking the others likely won't be far behind. You can get various coils of vacuum line very cheaply, especially online. Not that youy have to replace them all.

Pay particular attention to the ends of vacuum lines where the attach to other fittings. These areas are stretched more than the rest of the line and will usually be the point of first failure.

My TJ acted very similar to your vehicle. Turned out the vacuum line at the canister under the battery tray had cracked right a the fitting. $3 worth of hose later it was fixed.

 

thank you very very much. time to do some hunting with the flashlight.