So removing the heater core on a 2003 Jeep Liberty 3.7 v6, the hvac box has to be removed to replace heater core? Mine is tore down and without removing the hvac box that the heater core is mounted into, their seems to be no room to remove it. Is this correct? And why does aluminum ac lines have to be disconnected? Are they plugged into lines going into hvac box? And after doing this and putting back together I need to have a flush done on my ac system I’m assuming?
I don’t know about the Liberty in particular, but on many vehicles, the entire HVAC plenum has to be removed to get access to the heater core. The evaporator for the AC is inside the plenum. So you’ve got to disconnect AC lines to remove the plenum. And yes, it has to have a vacuum pulled and refrigerant put back in. Fun! Went through this on my 98 Dodge Ram I owned years ago. 94 Chevy Silverado, the heater core was accessible without all the drama. Sometimes it makes you wonder why automakers do some of the things automakers do.
So by the term “plenum” your referring to the black housing box behind the dash that contains my blend door actuators and all that Bc that’s what my heater core is sitting inside of.
Yes, that’s right.
Have you looked for videos on YouTube on removing the heater core on the Liberty? Maybe someone’s posted a good video, might help.
Usually heater core jobs are as nasty and complex as they appear… and if you need to break the AC lines in the process then yes, you will need to evac and recharge that system.
Welcome to heater core replacements. Have fun… I’ve seen people junk cars over this repair.
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Yes unfortunately I haven’t found any videos that really show my year model on how to remove it but I’ve already removed every other part of the dash, it got dark on me outside so tomorrow morning I’m on it removing the ac lines and this hvac box surely it won’t be too bad, hoping I can remember how to put it all back together.
Honda blackbird I honestly have never wanted to get rid of this thing but lol I was earlier talking to my gf saying “you know, I may just trade this bastard off” 
I did it on my 98 Dodge before YouTube videos, or at least before I knew about them. I did have a Hayes (Haynes?) manual I picked up at the parts store. It was more time consuming and “I hope I don’t break this plastic chit” than it was difficult. Most of the wiring and vacuum hoses disconnected at junction blocks and could only be plugged in one way, so less chance of mixing up wiring and hoses. I had a shop pull a vacuum on the Freon and reinstall Freon. I did the rest. I took my time. I think I finished at like 3 am 
How serious is the whole thing about vacuuming the Freon out of my lines before removing the ac lines
You’ll want to pull a vacuum before you put refrigerant back in. I believe vacuuming it out beforehand is more for the environment than your vehicle. That said, the shop that did mine didn’t charge any extra to pull it out than they would’ve for just filling it with refrigerant, so they said. But I drove there and had it done before I started working on it.
Well It’s a little too late to take it to a shop now lol oh well
Besides evacuating the a/c system, you’ll want to have the a/c specialist replace the “receiver/dryer”.
I didn’t, myself. No issues. I guess I drove the truck another 50k miles and 3 years. AC was fine when I sold it.
Not arguing with you, as that may be the procedure. I’m no expert. But I did not do it. I did plug the AC lines at least.
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So basically, the design is to replace the heater core, your going to destroy your entire ac system
It’s all good scrapyard John, just a bs design on how they made these things
In the old days you could replace one in about an hour. I lucked out on my Riviera. Had the manual and thought I’d have to cut the car apart but it wasn’t too bad-but I’m small and flexible.
Really the factory manual would have the step by step procedure. It might be worth getting the All Data subscription just to make sure if there are any short cuts. From what I have seen, it is essentially a copy of the factory manual.
The instructions I’m seeing are pretty sparse, but heater core replacement is spec’d as an 8 hour job. The 8 hours includes all the instrument panel work, but the refrigerant evacuate and recharge part of the job is extra. All in all for a diy’er who’s never done it before, and the vehicle is equipped w/AC, I’d guess you’d be looking at a 20 hour job. Not the end of the world, 5 afternoons @ 4 hours each. But it is a big job.
I seem to recall @db4690 telling us that one particular Mercedes was essentially built around the heater core and that a change out could cost $thousands.
In a recent Best of Car Talk podcast, one of the callers was asking Tom & Ray if he could do this as a diy’er job. Ray said the problem is that when the car was built at the manufacturing plant they started by hanging the heater core from the ceiling, attached by wires, then they built the rest of the car around it … lol .
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The R107 roadster series . . . those would be the 450SL, 380SL and 560SL here
Some smarty pants is probably about to point out that there were other roadsters in that series, but they weren’t sold here in the USA. Any 300SL with the 103 engine . . . to cite just one example of the others . . . registered here in the USA is a gray market car and didn’t arrive through regular channels
And yes, it did seem the heater core and evaporator were built around the car. The book time to replace them was staggering.