Well it's doing it again my Cherokee has an issue with the vacuum operated control that switches from blowing out of the vents to the defrost. When I'm accelerating onto the interstate it will stop blowing,but when I let off the gas it starts back. anyways has anyone else had this problem?

 

higher engine speed= less vacuum
lower engine speed= more vacuum
and for the vents prob. use search

 

Just curious if you have installed any after market intake/airbox gadgets. I had installed a maxair intake and all of the sudden I started having the same problem. Went back to the stock airbox and the problem went away. Otherwise you can check the vacuum container that controls the ventilation for your jeep and make sure there are no leaks in the container or lines. Depending on what year jeep you have will dictate where the container is. I have an 88 and it's near the passenger side bumper.

 

My Cherokee is a 95 and my vacuum container is in the front bumper and I checked it. I have the stock airbox and I have went over every single vacuum line under the hood. I have never taken the dash apart and I don't know if it's worth fooling with since summer is going fast.

 

Ok, I'm having the same problem with my 99xj, when i get on the gas the ac will blow out the defrost and when i let off it goes back to normal, it will also squells (sounds like nails on a chaulk board) from the dash when i'm on the gas, if someone can help it would be very helpful...

 

Theres a vacuum line on the pass side of mine when i shut the jeep off i can hear it creak shut and I can hear it leak when the hood is open it's a orange line on the passenger side.