I have a 98 XJ 4.0 with manual transmission. For the past month I have had a strange thing happen while driving down the highway with cruise set. Whenever I get to an incline, my fan for my heater kicks into high and almost seems that it changes to defrost instead of heat. I do not have it switched to the setting where the AC would be used either. It goes back to whatever setting I had it on after getting back to level ground or if I kick off the cruise. Just seeing if anyone else has had experience with this issue. Thanks!

 

Yep. I have seen tons of discussions here about that problem. Google will have results also.

http://bit.ly/1zUzKqF

 

Here's a link to photos of the vacuum tubes in the engine bay. You may want to inspect them all for cracks or chafing/broken.


https://www.cherokeeforum.com/g/album/3212409


Click the images to make them larger.

 

The check valve in the vacuum ball is one possibility. On the long climb the manifold vacuum is low. Somewhere it's leaking, and defrost is where it goes without vacuum. The ball is there to hold/supply vacuum, while the engine is not making much.

Nice pics Ken! I see you found HVAC uses the driver's side of the reservoir. (ball)

 

The Modern XJ's don't have a check valve in the reservoir - only the covered wagon Renix types do. The check valve is at the intake manifold in OUR Jeeps. LOL

As I recall it was your leadership that named the driver's side as HVAC (see photo credit).

 

??? All I said is I'll check! (I never did). Pretty academic, anyone there should figure it out. I mean with the ball out both ends should be checked.

And hey, where would we be without covered wagons. eh?

Thanks for the heads up on the check valve...91 or 97 I wonder?

 

Here's a pic of a '96 intake check valve I pinched off another forum the other day. Need to add it to my collection.


I think this '96 set up is the same for the 91.

 

HaHa. Of course the joke is, what month in 96? (the transition year).

I'll go with 91. That's the year they eliminated allot of neat features to cut down on production cost. With the valve there the ball is cheaper for them to build. No more disco, no more heater valve, no more "comfort" option. That must have saved (Chrysler), $100's of dollars per/unit.

Now with a leak anywhere in that 10 foot line, your controls go out. Another "improvement".