'01 Limited Sport, just picked it up and working my way through the issues/repairs it needs. The vent/air direction control **** doesn't seem to do anything, air always comes out from the defrost vents. Checked the vacuum reservoir ball behind the bumper and it doesn't appear to be cracked, even hissed at me when I unplugged the line which indicates to me that it's not a vacuum issue. Could the vent control **** be bad, or could it be some sort of linkage/door behind the dash that's stuck? Not sure what to check next and don't want to throw money at it blindly.

Thanks.

 

I had a similar problem. Defrost door actuator is in full defrost mode with no vacuum applied. Not saying this is what’s going on with your XJ but this may help a bit.

 

Might want to check your vacuum lines anyway. They start at the manifold and cross along the firewall to a "T" where the heater hoses enter the firewall. The black vacuum hose should come off the bottom of the "T" should enter the firewall there. That line provides vacuum for your HVAC. The main hose goes on to the passenger side and runs your cruise control before going to the reservoir ball. My point is the line could be capped at the firewall by the PO. Stranger things have been found!
Good Luck!

 

That little vacuum line could be broken. It is plastic and gets brittle over time

 

I had the blower motor set to 2 and listened while I switched between face and feet on the vent control ****. I can hear a vacuum hiss going from feet to face, but not the other way. So it sounds like I have vacuum at the ****.

Haven't checked the two bell actuators behind the dash yet. Just finished replacing belt, water pump, and thermostat and the 'ol back is a bit sore now.

 

Just checked vacuum at the T on the firewall and it was 15 on startup/idle, 20+ when revved.

It's hard to see those actuators behind the dash. Turning the vent control **** to any position only seemed to move the one marked panel/demist in the above photo. The two for floor and defrost vent actuators don't move at all, but defrost is always blowing and sometimes I can get a little to come out of the floor vents. On the back of the **** are multiple colored vacuum lines. I can only see where brown goes, the floor vent actuator. I definitely can't see if any linkages are broken, would have to pull the dash for that which I'm not too excited about since it's probably a PITA.

I checked and re-checked all the related vacuum lines under the hood up to the one that goes from the T and through the firewall. I can find no signs of a leak in the system anywhere.

 

Found this guide where they tested different sections of the vacuum system, so I'm going to try that with a mityvac pump. They said if everything is good up to the air direction control ****, then you can turn the ****(with vacuum applied and engine off) and whichever position causes vacuum loss points to the leaking actuator. I'm hoping in my case that it's just a bad line or control **** because I really don't want to pull the dash to replace an actuator.

https://www.4wdmechanix.com/How-to-J...ioning-Fix?r=1

 

So the coincidental failure of both the cruise control and the ducting is probably a vacuum leak?

 

This thread is 3 years old.

Btw, fixed my issue by replacing the hvac controls with a new set from ebay. The original had an internal leak that vacuum testing with a mityvac exposed.