It has finally come time to replace the heater core in my '99 XJ. I have previously done this on my '98 (https://www.cherokeeforum.com/f2/yet...thread-267570/). Learned from that one and going to get a copper/brass heater core. Also glad to see you can still get the foam for the heater box seal to the firewall. The one thing I did not do on my 98 was replace the vacuum line from the air location selector in the cabin that runs through the firewall into the engine compartment (black line circled in the picture below). Are there any options for replacing that vacuum line or am I better off patching a silicone line of some sort? The current one is patched in the engine compartment since that gets brittle and eventually breaks. Once it breaks, you only get air directed at the windshield.
These pics are from my thread of trying to patch this on my 98. I have never messed with the vacuum lines on the control dial, but they do not look serviceable at all. Thanks a lot Jeep designer Bob. You suck.

 

My vacuum lines felt very pliable, including the main black line coming from the engine compartment, so I left them alone. If yours is brittle or you think its going to become brittle, seems like proactively patching it is the way to go. I have no experience on repair/patch though. My first thought would be to slide it over a piece of small diameter metal tubing, maybe some 1/8" stainless steel tubing used for swage fittings.

 

You can see in that DeXJ screenshot there is a little rubber hose splice behind the firewall on top of the air box. I just disconnected it there and got a new piece of vacuum tube from the parts store.

 

I've repaired my vac line breaks (when I can reach them) using some heat shrink tubing. I cut clean ends on both pieces, slip on a generous length of HS tubing and butt splice them back together.

 

Check your defrost flapper door vent arm condition while you have the box out. It can still be reached with the dash in by removing the radio, but you might as well do it now while it's easier. Mine has failed and I have to remove the radio to push it back into place every now and then.

Lube up the pivot points for easier operation. I use dielectric grease as it's silicone based and I figure that's better for plastics than your more regular automotive greases.

I also recommend removing the plastic "chimney" fresh air vent that goes into the cowl and resealing it permanently. The factory used some foam that degrades over time and causes leaks after two decades have passed. I used window polyurethane to seal mine up. No time like now.

The box seals on the exterior are now available cheap on the aftermarket. $10 instead of the $50 I paid back in 2020.

 

Inside the cabin is still soft and pliable. It's jsut that little part in th engine compartment that is brittle. I have patched it already and luckily there was some coming through the firewall. I'll order some silicone tubing from amazon and patch it in. I don't recall seeing the splice on top of the heater box. Thanks for the replies. Hopefully getting to this in the next few weeks. Been really cold here in northern Va.

 

IT's almost 60 here in Northern Va. so decided to tackle this fun job today. The dealer had replaced the AC evap core 15 or so years ago. In retrospect, I doubt it was the evap core but that's a differnet discussion. Found that one of the heater box studs was missing a nut. I suspect this is what caused a different problem I had with the O2 sensor blowing a fuse. But I would be digressing again. The forst two nuts were spinning on the studs. Got one off with some vice grips grabbing the stud. Working on the other one. HAven't tried the other 2 yet. I'm guessing the nuts got put on with power tools. Like the spanish inquisition, always expect the unexpecte. Hopefully have a better update ate today.

 

Speaking of the Spanish Inquisition, that one stud hidden behind the head is fun to get to. I recommend poking it with some soft cushions.

 

That was one of the ones that the previous mechanic did not put back. Took longer than I waned, but victory is mine today. Took a dremel to the nuts. Verified the heater core was in fact, done for. Was going to reuse the receiver drier, but I could not get the AC line disconnected from that side. The other side relented. So dremel tool for the win again. Should replace that anyway. Can clean it all up and start reassembly tomorrow.Started around 1:00, took a break for lnch. So 5.5 hours. Must have wasted an hour and a half messing with the nuts and the receiver drier.

 

Got a late start, but got the heater box back in. Was going to try to get the inside done, but then realized the pillar plastic piece got stuck behind the dash somehow. It goes down pretty far so no way I can pull it up. Hopefully 10 minutes to pull the dash bak enough t pull it out. Used some JBWeld plastic/metal to secure the studs into the heater box. Seems like a dumb design. But then again, as long as it lasts long enough for a warranty, manufacturer dn't care. Even put all 5 nuts back on. Was getting dark and I didn't feel like getting pics. This sis the trim piece I need to fix.

 

Got finished today. Roughly 12 hours over 3 days. Waiting on an AC receiver drier to finish the AC. I've done my 98, now the 99 and did my 95 YJ heater box 8 or so years ago. Hope I don't have to do anymore.....ever. I ended up getting some for the vacuum line that goes through the firewall. Left some extra to keep it away from the heater hoses.

 

For future reference. I ended up getting this copper core heater core from radiator express.

 

Good price. My copper/brass heater core was twice the cost. Did yours have any manufacturer tags on it?

 

It had a sticker on the side that said Made in Mexico. Had some other info on it, but I didn't take a pic. Hopefully it was a good choice.

 

Drat. Put the new accumulator/receiver/drier in today and thought I'd be done recharging the AC in an hour or so. The Pope of nope came for a visit. I could not pull a full vacuum. Something is definitely not sealing all the way in the AC system. Spent 3-4 hours trying to figure it out. Pulled all the connections, replaced orings, compressor port seals. Nada. Will try a smoke test next.