Sorry to bring up this topic again, I know there are a ton of posts regarding this issue but im about to throw in the towel and just live with the heater on defrost. Recently replaced a missing vacuum canister, also replaced just about every vacuum line on the XJ. The main vacuum line that operates the vents was super brittle and did have some holes in it. I replaced the line and used heat shrink over the splice to ensure tight connection. I was positive this was gonna fix the issue. To my surprise its still stuck on defrost. Vacuum canister is holding vacuum. The only thing left of that i can think of is the actual heater control in the dash or a busted line behind the dash. Dont think I want to tear into the dash, might have to tap out on this one. Any other suggestions that i can troubleshoot?

 

anyone have any suggestions?

 

If you're certain there are no other leaks before it runs into the firewall, then the heater control is next. Up can pull the radio out to get more room and more visibility. Then remove the screws holding the HVAC controls and pull it out slightly (no need to remove it yet) so you can get a good look at the back of it.

It will look something like this. You can see the plug with all the vacuum lines (they are all cut off in this pic). Make sure the plug didn't slip out. Try to check the lines themselves for any breaks. I think the black one in the lower right side is the line coming from the reservoir.


Here's the vacuum schematic to shows the vac lines connections to the different door servos..

 

thank you for the pic you posted, that is very helpful. Ill take a look back there and see what im able to find. again thank you for the info

 

*UPDATE*

so im not sure if the vehicle needs to run awhile to build up enough vacuum but recently after finishing the open cooling conversion, I had the Cherokee running for a bit to check for leaks, while doing so i turned on the ac for a bit to check fan and also for some relief from the heat. To my surprise cold air was blowing out the vents. Surprised i checked the heater and heat was blowing from vents as well, changed to floor and defroster and both worked as well. Not sure what happened before but its working now