Another heater core replacement (and A/C Evap core)

MountaineerTom

LJ Enthusiast, Retired USAF Weapons Loader
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Location
Sumter, SC
2006 LJ with A/C.

Earlier this year, I seen the first signs of heater core leaking from the air box tube. I knew it was coming because I could smell a very faint smell of coolant in the cab every now and then. Initially, I didn't plan to replace the A/C evap core, but after thinking of everything involved, I decided it would be best to replace it while I was in there.

I ordered MOPAR heater core (P/N 5073180AB) and A/C evap core (5073178AA). I also bought this O-Ring kit and Pag Oil from Jeep Air so I could replace the O-rings, and lube them, where the lines and evap core connect.
The MOPAR heater core has been discontinued. Others have had success with a core from Performance Radiator.

I took the Jeep into a shop and had the A/C evacuated. Once I got to the part of the job where the A/C lines get disconnected, I used these Lisle a/c, fuel line disconnect tools to disconnect them from the core. I've had this set for years, but have only used them on various fuel lines, but they worked great on the A/C lines. Then I covered the ends of the lines with rubber gloves and a rubber band to keep contaminates out.



I started by making some homemade hose pinchers out of some stuff lying around the workshop so I didn’t lose too much coolant from the heater hoses.

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When disconnecting electrical connectors, I used painters tape and labeled them. For connectors on the steering column, I just labeled them like top of column, bottom of column, etc. For connectors around the firewall, I just labeled each end "A", "B", etc. Whatever works for you so you can remember.

The steering wheel will lock if you turn the wheel about 1/2 a turn then shut the engine off and remove the key. You don't want to turn the steering wheel once the column is off so the clockspring doesn't break. Once removed, the steering wheel shouldn’t turn as long as you don’t put the key in, unlock it and turn the steering wheel. Also, as long as you don’t turn the front wheels left or right, it should all go back together pretty smooth when you reinstall it.

I ran into my first snag that I don't remember seeing any info about on other write-ups. Maybe the ones I seen were manual transmission. Mine is an auto and has the Brake Transmission Shift Interlock cable that runs from the ignition switch to the transmission shift. The factory service manual says, "With the ignition removed or in the unlocked position, disengage lock tab holding cable end to steering column."

I had already pulled the battery and rotated steering wheel 180 degrees to lock it. I just held the steering wheel in position, turned key forward to unlock, disengaged and removed the cable from the ignition then pulled key and made sure steering wheel was still locked. It worked well.

I disconnected and removed the switches in the door jams for the dome and footwell lights after seeing a couple people had broken them in the removal/installation on the dash.

One other tip I'd suggest if you're going to turn the wheel and lock it. Loosen the pinch bolt where the shafts meet before turning and locking steering column. It will keep the bolt head on the bottom where it's easier to get to. It was pretty tight and hard to get to when rotated on top like I had done. Loosen it first, then rotate and lock your column. Remove the pinch bolt completely to pull the steering column out of the Jeep. There is a groove in the column shaft that the bolt lines up with and the column won't come out until you remove the bolt.

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I folded back the sunrider feature of the soft top to let more light in while working on things. It was a big help. It gave me a little more head room too when pulling the dash up and out. I decided to remove the instrument cluster and radio for two reasons. 1) it kept them from getting scratched up while laying on the drivers seat. 2) it made it easier to look around to make sure everything was disconnected.

Some things I needed to do that some might not. Removed the passengers side door surround, a-pillar trim, sunvisor and popped the top windshield trim because I had a harness that I made that runs up to the auto-dimming rearview mirror.

Pulled the passengers side carpet in case coolant leaks out when I pull the HVAC box out.

A member on another forum, Gottagofast, said he of laid the dash on the reclined drivers seat when he did his. It worked out great for me too.

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There are 5 studs on the HVAC box that go through the firewall. You can see them in one of the pics below, they have the white plastic washers on them. One of them behind the valve cover has 2 nuts with the cowl drain sandwiched in between them The cowl drain has to come out, so remove the first nut, remove the cowl, then remove the second nut. The HVAC box isn't going anywhere until they are all removed. I don’t recall seeing this on some of the other write-ups I’ve seen. After getting all the nuts off the firewall, I could still feel a little resistance when trying to pull the box back and out. On my ‘06 there was 1 screw holding the box to a support bracket inside the cab (circled in red). After removing that, the box came out easily.

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My new evap core didn’t come with a brace that goes on the two lines, so I just swapped the one from the old core over. Cleaned the box out real good with a little 409, put a little lithium grease on the pivot points of all the doors.

Two silver clips that help hold the 2 housings together. Cover them with your hand so they don't go flying during removal. Luckily I seen where the first one went and didn't lose it. The second one I covered with my hand.

I don't know how many screws had to be removed to separate the box. There was a bunch around the outside, but also one on the bottom. I removed the intake for the fan to make it easier to get to some of the screws.

All my foam gaskets are in pretty good shape for 12 years old. I was able to peel the one around the cores input/output tubes and set it aside until reassembly. One of the bigger round-ish gaskets, I just peeled the bottom half off and left the rest connected to the top half. I'll find some kind of adhesive to put on there when reassembled.

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Earlier in this post, I mentioned removing a screw that was holding the HVAC box to a metal tab inside the cab (the pic with it circled I red). I kept that screw in that nutplate while everything was out so I didn’t lose it. Well, I forgot to pull it out before installing the HVAC box and it wasn’t lining up right. So, don’t forget to remove it before installing all the firewall nuts or you’ll be pulling them back off to pull that one screw out (if you kept it in the nut plate). On the plus side, you’ll be skilled at those firewall nuts. : )

Speaking of the firewall nuts, if you have a small extendable magnet, it will make putting those nuts behind the valve cover a piece of cake. And a ratcheting wrench makes them easy to install and remove.

I also used a bungee cord attached to the grille brace rods to pull the wiring harness away for more room for my hands.

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Overall, not hard at all, just time consuming like everyone says. The reassembly was way quicker than disassembly just because I knew where everything was. The only real killer for me was just not having the time to get it all done in a day or two. It took me almost 3 weeks of working on it on-and-off between working 12 hour shifts, family visiting and other things needing to be done around the house.

Got it all finished up, let it run for 20 minutes or so while I cleaned up tools and stuff. No leaks. Test drove it for a little bit. No leaks. Let it run for about 45 minutes while I put the side windows and passengers seat in and cleaned up more stuff. No leaks and lots of heat. I drove it around for a few days to make sure it’s still wasn't leaking then got the A/C recharged.

I had 1 screw like the ones that hold the HVAC box together left over. I went over and over that thing looking for where it went and couldn’t find a spot for it. I even disassembled the box just to make sure I didn’t miss something that may have been on the inside and found nothing. Everything works though like it should.

I also decided to take a closer look at the passengers side seat while it was out. On the inside, the seat back never seemed like it was locked in to place and would lean back a little. I undid the fabric thinking maybe a weld broke on the frame. Felt around up in there and found nothing wrong. Looked around the hinge area and seen a dime wedged in between some of the parts. It was in there tight. While pushing and prying around on it with a screwdriver a penny fell out. Still couldn’t get the dime out, so I removed the bolt for the seatbelt latch and had room to get the dime out. Seat back feels tight and secure now.
: )
 
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Thank you! I’ll be stealing this … Got the sweet smell of a leaky heater core … this is the most dreaded job I could ask for. But you made it look nice and easy!

I got a brassworks core being built and a mopar evaporator en route … thinking of doing the AC evaporator, lines and compressor since I have about 150k miles on stock components. Been loosing AC charge over the course of summer, still cools but lost its chill.
 
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Excellent write up! Wish I would have read this before I did mine. I also left that screw in place in cab and had as well as I was left with one screw for the air box that I could find a place for. I also purchased an evaporator just in case from Amazon thinking it’s easy to return if I don’t need it. I definitely needed it as wine of the lines in the evaporator was super loose and leaking
 
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I pulled my dash yesterday and replaced the whole HVAC box. Here are my observations in addition to the excellent writeup from @MountaineerTom

1) I did not remove the steering column - merely used a couple of straps to hold the dash out of the way. I was worried that it was going to be harder this way but it really wasn't and there was plenty of room to work. I got the HVAC box out and back in again by myself - with a sprained wrist so its just not as tough a job as you think. You save a heap of time by not removing the steering column.

2) The electrical connectors were all pretty self-evident (noting I didn't need to do the ones around the column) so putting them back in was literally a 2 minute job with no confusion as to what went where. I didn't need to mark them as the colour code was self evident.

3) On my TJ (RHD note) the cowl drain is NOT fastened with the same nut as the back of the HVAC box so if you have a RHD you do not need to remove that cowl drain which is good as its a pain in the ass to get to!

4) I took a big piece of cardboard and carefully poked holes and placed each screw in exactly the right spot so I wouldn't be confused when reassembling. I now have two spare screws with NFI how that happened so if Tom only had 1 spare he is doing better than me!!!

5) When reassembling your HVAC box - put the top on carefully and make sure that its seated on all sides, I had to fiddle a bit to get the blend door hinge to seat properly.

As countless others have said, whilst this looks like a big job, in practice it wasn't anywhere near as bad as I feared it was going to be. About 3 hours to get it all out and maybe 1 hour to get it all back in. If I did it again I reckon 1 hour each way...
 
@Bammo68 3 hours apart and 1 hour to get it back together? I hope that's the case. I'm about to start this job in a day or two.

If I had one piece of advise, it would be to label everything. Everything! Most of it is easy to figure out where it goes but it seems like there is always this one connector or screw that you have trouble with. Especially if something happens to cause a delay in finishing the job.

I still have an extra screw from it that I have no idea where it went. Couldn’t find a place for it. LOL
 
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If I had one piece of advise, it would be to label everything. Everything! Most of it is easy to figure out where it goes but it seems like there is always this one connector or screw that you have trouble with. Especially if something happens to cause a delay in finishing the job.

I still have an extra screw from it that I have no idea where it went. Couldn’t find a place for it. LOL

I already have plans to put a big piece of cardboard on my second workbench, put all the screws on that cardboard, and label them. I'm not so worried about the connectors because I've found that pretty much every connector can only plug into a single spot in the vehicle.

I'm probably going to start within 1-2 hours. My current concern is whether I need to take out the steering column or not. Some say to do it, and others have been able to get this done without taking off the steering column and using straps to hold up the dash.
 
I already have plans to put a big piece of cardboard on my second workbench, put all the screws on that cardboard, and label them. I'm not so worried about the connectors because I've found that pretty much every connector can only plug into a single spot in the vehicle.

I'm probably going to start within 1-2 hours. My current concern is whether I need to take out the steering column or not. Some say to do it, and others have been able to get this done without taking off the steering column and using straps to hold up the dash.

It probably can be done easy enough with the column in. I chose to remove mine because I knew from the start it was going to take multiple days working on and off with it due to my work schedule at the time. I figured if I just moved it completely out of the way it would be easier.
 
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I just finished up my heater core replacement, and here are a few additional steps/advice.

1. You don't need to take out the steering column. You can pivot the dash around the steering column in place. However, if you do this, put something protective over the top of the steering column because the metal in the back of the dash can dig into the plastic on the steering column and leave some scratches.

2. If you leave the steering column in place, you'll likely need to loosen the center console. This is because there are vents at the bottom of the dash center piece. You can remove the bottom vents though. There are 2 screws in front and 1 hidden in the back that is hard to get to. If you remove this, you will have enough clearance to get the dash out. If you loosen the center console, you will also have enough clearance. If you do loosen the center console, the shift indicators are pretty fragile and can easily break.

Basically, you have to pick 1 of these 3 options: 1) remove the the steering column 2) remove the vents at the bottom of the dash or 3) loosen up the center console.

3. The instructions I've found online to take apart the heater box have been lacking. My There are something like 13 screws. Can't remember the exact number. Also, there are 3 screws to take out the blower motor, which on my heater box, you have to do. Now, with the blower motor out, as well as all the screws, and the 2 clips, the only thing holding the heater box together is foam and sealant. You can find the seams in the heater box around the blower motor hole. I took a knife and cute along those seams. For the foam around the rectangle with the holes for the AC evap and heater core lines, I took a putty knife and separated the foam from top section of the box. I didn't cut it at all. Foam was attached to the bottom section and could be reused easily. At this stage, there is just sealant keeping it together.The top spots for the sealant are around the blower motor, and the input for the 4 lines. Starting with the blower motor, firmly but gently separate the two halves of the box. I did this by putting a foot on the bottom of the hole and used both my hands to pull up. Once you get it to release, getting the AC/heater sealant to release should be pretty easy.

4. Definitely take out the door sensors on each side to prevent breaking them.

5.. This part is number 790159P and goes in this orientation. Whenever I pulled out the old heater core, it slid out too and took me awhile to figure out where it goes.

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I just finished up my heater core replacement, and here are a few additional steps/advice.

1. You don't need to take out the steering column. You can pivot the dash around the steering column in place. However, if you do this, put something protective over the top of the steering column because the metal in the back of the dash can dig into the plastic on the steering column and leave some scratches.

2. If you leave the steering column in place, you'll likely need to loosen the center console. This is because there are vents at the bottom of the dash center piece. You can remove the bottom vents though. There are 2 screws in front and 1 hidden in the back that is hard to get to. If you remove this, you will have enough clearance to get the dash out. If you loosen the center console, you will also have enough clearance. If you do loosen the center console, the shift indicators are pretty fragile and can easily break.

Basically, you have to pick 1 of these 3 options: 1) remove the the steering column 2) remove the vents at the bottom of the dash or 3) loosen up the center console.

3. The instructions I've found online to take apart the heater box have been lacking. My There are something like 13 screws. Can't remember the exact number. Also, there are 3 screws to take out the blower motor, which on my heater box, you have to do. Now, with the blower motor out, as well as all the screws, and the 2 clips, the only thing holding the heater box together is foam and sealant. You can find the seams in the heater box around the blower motor hole. I took a knife and cute along those seams. For the foam around the rectangle with the holes for the AC evap and heater core lines, I took a putty knife and separated the foam from top section of the box. I didn't cut it at all. Foam was attached to the bottom section and could be reused easily. At this stage, there is just sealant keeping it together.The top spots for the sealant are around the blower motor, and the input for the 4 lines. Starting with the blower motor, firmly but gently separate the two halves of the box. I did this by putting a foot on the bottom of the hole and used both my hands to pull up. Once you get it to release, getting the AC/heater sealant to release should be pretty easy.

4. Definitely take out the door sensors on each side to prevent breaking them.

5.. This part is number 790159P and goes in this orientation. Whenever I pulled out the old heater core, it slid out too and took me awhile to figure out where it goes.

View attachment 476778



View attachment 476779

Good info. 👍🏼
 
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