Ive got a 98xj that doesnt switch to any vents other than defrost.

Vacuum system seems to be working fine. Cruise control has no issues. I also disconnected every vacuum link from the ball to the engine block and tried to blow air through to check for leaks. Doesnt seem to have any leaks.

Is replacing my control switches the next step?

 

Look for a broken tube to the HVAC check valve/tee. Not all XJ's have a check valve. If you have a check valve and it's defective the HVAC vacuum system may not work but the cruise control will.





Fix for broken tube:





HVAC Check valve:

 

Thanks for the thorough reply. My HVAC selector hose was cracked and I have repaired it like in the picture. However this did not resolve the issue.

What should I look at next?

 

Those plastic lines are difficult to thoroughly check. You found one leak, and you likely have more. Check every inch with your fingers as well as your eyes. Any rough spots you can feel are likely to be a break or abrasion where a leak will occur.

 

You might want to test the entire system (except the check valve at the intake) using a hand vacuum pump. A brake bleeder type from Harbor Fright.


See pic. I removed my engine so I could show you where you plumb it in. :-)


The HVAC door actuators only need around 8 in/hg to operate. You can pump the system down to around 20 in/hg and let it sit. If it holds the engine bay vacuum system is tight.


If it holds, you can check the operation of each HVAC door one at a time. Listen for the door(s) to operate. You'll have to pump it down often to do this.


Edit: Forgot to post the pic...silly goose.

 

As it turns out the issue did resolve. It was the selector line repair that did it. It just took my xj a commute to normalize the pressure. Thanks for all your help CCKen.

 

Good.