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How to replace the heater core on a Jeep Wrangler TJ

JFjeld

TJ Enthusiast
Dec 10, 2015
125
-- Write-up created in 2007 --
So I just bought a used Jeep Wrangler with a 30-day warranty from a small local dealer. Almost immediately after the 30 days, I began to smell antifreeze, had trouble defrosting, and was noticing tiny droplets of an oily substance on my passenger floor. The obvious diagnosis was a leaking heater core. Calls to local mechanics, dealers, and small repair businesses revealed estimates of $550 to $850 dollars. The part itself was about $75 but the job was extremely labor-intensive. The entire dash had to be removed, along with the entire heater / a/c housing assembly.

To save myself several hundred dollars, I decided to do the job myself. I went on the Internet and noted a few forums where people discussed heater core replacement, but I couldn't find any detailed instructions. Wanting to share what I learned, I prepared this document. I did consult a manual by a well-known corporation (who shall remain nameless) but it was more-or-less a broad topic overview.

I hope you find this useful. Note that I am not a mechanic. I'm a desk jockey who can turn a wrench and is stubborn enough to figure stuff out. If I could do this job, chances are you can too.

Tools Needed/Recommended:

- Metric & Standard Socket Set with various extensions and socket depths.
- Metric & Standard wrenches
- Assorted nut drivers
- Torx-head Wrenches
- Channel-locks
- Phillips and Flat-Blade Screwdrivers
- Flashlight and/or Trouble Light
- Plastic Baggies
- Permanent Marker


Notes:
- I removed my upper and lower doors (I have half-doors) prior to beginning the job. I wanted to be able to get under the dash with the least amount of effort and contortion.
- I found it useful whenever I was removing bolts/nuts to put those parts in a baggie and label the baggie with the particular step I was on. That way I didn't have to look at a huge pile of hardware and try to remember what went where.
- If you have a/c, it gets a little hairy since the refrigerant needs to be purged and the refrigerant lines need to be disconnected. If you are uncomfortable performing these steps and don't have the necessary equipment to keep the EPA happy, you should leave this phase to the professionals.
- Plan on a full day for the entire procedure. Or if this isn't your daily driver, do the job in phases over several days (steering column assembly, dash assembly, HVAC assembly)


The Job:

1. Disconnect and remove the battery. The negative cable needs to be disconnected to disable the air bags, anyway. It makes it a lot easier to get to the heater core hoses and housing-to-chassis nuts.

2. Drain the antifreeze from your radiator. Or, if you plan to have a professional radiator flush, you can skip this step.

3. Remove the entire steering wheel assembly, by performing the following:
- Remove the two (2) Phillips-head screws from the knee blocker and set the part aside.
- Remove the upper and lower trim pieces from around the steering column. This, too, is held by two (2) Phillips-head screws.
- Unplug all electrical connectors. Be sure to view the connector locks so as not to break any. Note that there are connectors at the top, bottom, and both sides.
- Remove the shift interlock cable (if so equipped) by turning the key to the "On" position and pressing the yellow tab. It will then slide out. Be sure to turn the key off and remove it so it doesn't get broken.
- Remove the switch bundle where it is tethered to the top of the column and allow it to hang to the bottom right.
- Remove the pinch bolt (1) securing the upper and lower steering shafts using a 13mm socket. This is located close to where the shaft enters the interior compartment.
- Remove the two (2) nuts securing the steering column to the cross-member of the firewall using a 13mm socket.
- Remove the two (2) nuts securing the steering column to the top of the firewall using a 13mm socket.
- Holding the wheel, allow it to drop down and then pull the entire assembly toward you, being careful to guide the cross member so it does not bind with the studs from the firewall. Do NOT allow the steering wheel to spin within the column assembly as it will damage the clock spring which will then need to be replaced! If the clock spring is damaged, you see issues with your horn, air bag light and possibly the instrument cluster when you reassemble your dash.
- Once the wheel has been removed, your Jeep should resemble this:



htrcore-1.jpg


Figure # 1

4. Disconnect the wiring harness connectors from the 100-way wiring harness unit on the left side of the inner panel. You can access it through the hole where your steering wheel was, or from underneath the dash. I had the following connectors, viewed from top to bottom:
- Gray
- Green
- Red I
- Blue
- Yellow
- Black I
- Black II
- Red II

5. Disconnect the driver's side defrost hose at the central duct, towards the middle by twisting and gently pulling.

6. Remove the glove box by removing the tether attached to the screw behind the right upper corner of the glove box. Once that is free, let the glove box tip down until it is free of its hinges.

7. Reaching into the cavity behind the former glove box, disconnect the following:
- Two halves of the heater / a/c vacuum harness connector. This has numerous yellow and blue hoses. As you disconnect it, you'll hear the air pressure being relieved.
- Two halves of the radio antenna.
- Air bag wiring harness connector (green).
- Any other wiring harnesses you can see but I failed to mention.
- Passenger-side defrost hose at the central duct, towards the middle, by twisting and gently pulling.
- Remove the two (2) nuts from underneath the passenger's side air bag using a 15mm socket.

8. Remove the upper cover from the dash. This runs the entire length of the dash and is about 3 inches wide. Gently pry one end up and work your way to the other side. This is held on with tabs, not screws.

9. Remove the three (3) Torx-head screws from each side of the dash using a T30 Torx-head wrench, where they attach to the door pillars.

10. Remove the four (4) nuts along the window where the dash is mounted using a 10mm socket.

11. If applicable, disconnect any custom switches you may have installed to the center console.

12. Straddling the middle console, lift the dash up and out, being careful that all lines/connectors have been removed. If needed, get some assistance when removing the dash.

13. The dash, removed as an entire unit, will look like this:

htrcore-2.jpg


14. Your Jeep, however, now looks like this:

htrcore-3.jpg


Figure # 3

15. If you have air conditioning, you need to discharge and recover the a/c refrigerant (i.e., "Freon", although that specifically, is no longer used). You then need to disconnect your refrigerant lines from the evaporator. This is necessary since the entire heater / a/c housing assembly will be removed from your Jeep.

I'm really not going to detail this since the EPA has gone to great lengths to protect our ozone layer from this stuff.
Suffice to say that these steps would best be performed by a professional. [See Figure 4]

16. Disconnect both heater hoses from where they enter the interior cabin. Notice that the top hose is larger in size, while the lower one is smaller. Take note of the hose orientation. The two ends of the spring clamps may be squeezed using a channel-lock pliers. Note that you may need to twist the hose to loosen it up. A coating of warm, soapy water may also do the trick, although you should avoid getting this into any openings. [See Figure 4]

17. Disconnect the vacuum supply line connector. [See Figure # 4]

18. Remove the L-shaped evaporator drain tube that protrudes from underneath the evaporator canister.

htrcore-4.jpg


Figure # 4

19. Remove the five (5) HVAC housing-to-chassis nuts using a 7/16 socket or wrench. [See Figure 5] They are found (when viewing from the engine compartment):
- To the left and bottom of the blower fan (1)
- Holding the evaporator canister bracket (2)
- In the middle, above the engine (1)
- In the middle, just above the cylinder head. Note that this one holds the cowl plenum drain tube. The nut holding the drain tube must be removed, the cowl plenum drain removed, and then there is another nut underneath. (1)

htrcore-5.jpg


Figure # 5

20. From within the cabin, remove the floor duct from the bottom of the HVAC unit. This can be done by removing the two (2) front and one (1) rear screws with a 7/16 socket or wrench. The duct can then be slid to one side and removed.

21. Remove the screw holding the HVAC unit to the firewall bracket, near the fuse panel, using a 7/16 socket or wrench.

22. Straddling the center console, slide the entire HVAC housing toward you, being careful to clear the center air ducts. Remove the entire system and place in a suitable area where you will now begin the disassembly.

23. Using a 7/16 nut driver, remove all screws holding the upper and lower HVAC housing halves together. Gently remove the top cover of the unit. I'll be honest; I had a lot of trouble here and had to gently pry the thing apart.

24. Remove the leaking heater core from the housing. When viewing the HVAC unit as it appeared in the cabin, the heater core runs across the back from the left side to the middle, where the tubes exit the housing.

25. If possible, clean the housing of any oil/antifreeze leftover from the formerly leaking core.

26. Replace the leaking core with the new unit.

27. Refit the upper and lower halves of the HVAC unit together and replace all screws.

28. Repeat all prior steps in the reverse order to reattach the unit, refit all hoses/lines, reassemble the dash, and reassemble the steering column.

29. Replace your coolant or have it flushed by a professional.

30. Crack open a cold one and give yourself some credit. Use the $500 you saved and treat your Jeep to some new goodies.
 
Last edited:
OP
JFjeld

JFjeld

TJ Enthusiast
Dec 10, 2015
125
I created the above write-up back in 2007, shortly after I purchased my TJ. It was originally submitted to Stu-Offroad (still available) since his website is such a huge resource for Wrangler owners, but I wanted to share it with this group as well. From the feedback I've received over the years, some folks have been successful with not removing the steering wheel and using paracord to suspend the dash, which apparently still allows for the removal of the HVAC box.

I had to repeat the job earlier this year; the heater core I bought in 2007 lasted about eight years. It was much easier the second time around. Hope the write-up will be of benefit to you. Feel free to PM me with any questions.
 

Chris

Administrator
Staff Member
Sep 28, 2015
38,136
Salem, Oregon
BTW, how difficult on a scale of 1 to 10 do you think this was? I have done heater cores on plenty of cars in the past, but never a TJ.

I cringe when I think about doing a heater core on some of these modern day cars with massive and sophisticated dashboards.
 

TJ4Jim

TJ Addict
Supporting Member
Dec 9, 2015
1,305
Brookings, Oregon
Chris, I did my son's TJ last year by myself and it really is just time consuming and requires patience, not really technically hard. I just took a lot of pics for memory purposes. One thing I did not do was remove the steering column, all I did was remove the support hardware and let it lay down, then I let the dash pivot on the column until it was far enough out for access to the heater box. I tie-wired the dash and let it hang from the roll bar.
 
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Chris

Administrator
Staff Member
Sep 28, 2015
38,136
Salem, Oregon
Chris, I did my son's TJ last year by myself and it really is just time consuming and requires patience, not really technically hard. I just took a lot of pics for memory purposes. One thing I did not do was remove the steering column, all I did was remove the support hardware and let it lay down, then I let the dash pivot on the column until it was far enough out for access to the heater box. I tie-wired the dash and let it hang from the roll bar.
Having done my fair share of heater cores before I know what you mean. I for some reason or another assumed that it would be easier on a TJ given how small the dashboard is in comparison to other vehicles.
 
OP
JFjeld

JFjeld

TJ Enthusiast
Dec 10, 2015
125
I agree that its not technically hard; just time-consuming. The second time I did it (earlier this year) went so much faster because I already knew what I was doing. Additionally, I converted my a/c to OBA a few years ago and didn't have to deal with that additional overhead.
 
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Chris

Administrator
Staff Member
Sep 28, 2015
38,136
Salem, Oregon
Friggin AC... I'm always so tempted to use it (being as though I NEVER use it), but having it there seems to potentially add to the resale value. Not that I intend to ever sell the TJ... But you can never say never, because you never know what life will throw at you.
 

Chris

Administrator
Staff Member
Sep 28, 2015
38,136
Salem, Oregon
In my neck of the woods OBA would raise it, not AC, just a thought for ya!
I know, I'm heavily considering that possibility. Even in the Summer when it does get hot, I'd rather have the top off and doors off than have the AC on. AC on a Wrangler seems so pointless!
 

John Carmony

TJ Enthusiast
Dec 7, 2015
145
Coldiron, KY
Here is another thought. How hard is it to reverse OBA? I have not researched at all on this. Is it possible to box up you AC parts and reverse at later date? Keep it in box, and *cough* if you ever sell it you have option of next owner AC/OBA ?
 
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TNHEADDUCK

Member
Dec 3, 2015
96
Music City USA
Come to the deep south in the summer and you will wish you had 2 air conditioners, 100 degree temps and 100% humidity equal bikini tops and Ac on max is the norm.

Jason
 

Chris

Administrator
Staff Member
Sep 28, 2015
38,136
Salem, Oregon
Here is another thought. How hard is it to reverse OBA? I have not researched at all on this. Is it possible to box up you AC parts and reverse at later date? Keep it in box, and *cough* if you ever sell it you have option of next owner AC/OBA ?
Yeah, I can't imagine it being that hard to replace it I saved all the parts.

Come to the deep south in the summer and you will wish you had 2 air conditioners, 100 degree temps and 100% humidity equal bikini tops and Ac on max is the norm.

Jason
Well, I've been down to Tallhasee to visit my uncle a number of times and I remember that being miserably hot!
 

TJDave

TJ Enthusiast
Supporting Member
Oct 27, 2015
119
San Jose, CA, United States
It always amazes me how fast we go backwards. The last heater core I replaced took a half Hour. Why do we let the auto designer geeks do things which exponentially increase the cost of ownership.
The newer vehicles get, the more efficient they get, but the harder they become to work on.

Imagine trying to replace the heater core on some 2016 BMW... God, there's so much shit to remove there it's insanity.
 
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billiebob

TJ Addict
Supporting Member
Oct 31, 2015
3,837
Kootenays, BC, Canada
The newer vehicles get, the more efficient they get, but the harder they become to work on.

Imagine trying to replace the heater core on some 2016 BMW... God, there's so much shit to remove there it's insanity.
Imagine this.... dead battery in anything German? The Guidelines for Tow Companies say deck it to the nearest dealer... imagine that on Dec 24th....