when driving my Cherokee i noticed it has started to re route air to the defrosters if i go over a certain speed. It re-routes it back to the main vents if i let off the gas a little. has anyone experienced this before or is it common? thanks!

 

Check the vacuum reservoir behind the passenger side of the front bumper for cracks. Also check the vacuum hoses for breaks and leaks.

 

Also check the check valves in the vacuum lines. Check valve off of manifold took care of my issues.

 

so this is a common issue? i normally check them all but will give it one more shot! thanks!!

 

just checked all the vacuum lines i know of and they all look fine?

 

Check the vacuum reservoir behind the passenger side of the front bumper.

 

i did and its connected... really weird

 

Did you check ALL of the check valves?

 

all that i see

 

Is the reservoir in good condition? Any cracks or holes in it?

 

The mode doors are vacuum actuated, so when it loses a certain amount of vacuum for so long by having your foot so far into the throttle, the system defaults to the defrost vents until the vacuum canister is back to normal. I've noticed the same issue with mine.