Here you go, Blake, (and everyone else):
To start off, changing the evaporator and the heater core are the same job, and it's a big one. This isn't for the faint-of-heart. If your GX/ 4Runner isn't your daily driver, you have a few days, you're mechanically inclined, you could do it. I now see why shops charge $1000 or more for this job....
You will have to evacuate the AC and drain the coolant from the radiator. You'll have to disconnect the heater core lines at the firewall, just above the DS valve cover. Disconnect the battery, too, obviously.
I bought an interior trim kit tool set from NAPA for $16. It makes interior panel removal very easy without boogering them up with nicks and scratches. The other tools needed are 10mm socket, 12mm socket, 14mm socket, phillips screwdriver, 12mm racheting box end wrench, and a 4mm allen wrench.
As far as interior panels that need to be removed:
(I laid the pieces out in the order removed on my bench so I knew what order they needed to go back on.)
Center console. The rear part that has the storage and rear hvac controls can slide back a few inches.
The shift knobs unscrew. But, the gear shifter knob has a chrome trim clip at the base that you'll need to unclip using a trim tool. There is a zipper for the ebrake handle.
All surrounding trim panels of the center console.
Stereo system head unit.
Both AC duct panels that flank the stereo.
Glove box and surrounding trim panels
Left and right ac ducts
Wood trim panels in the middle of the dash
Lower dash below the steering wheel
A Pillar covers, held on by the oh-$ hit handles. *If your windshield guy was lazy and didn't remove these covers when installing your new windshield, there will probably be windshield sealant oozed onto the fabric, requiring you to cut them free and repair the cloth!* Take your time and trim the fabric with a razor. You can stretch the fabric and reglue it if you don't rip it to shreds.
Rocker trims and kick panels.
Gauge cluster. There are 2 tiny clips on top of the gauge bezel that get removed. The bezel then just pulls out. You can only do this after the DS lower dash it removed. The gauge cluster is held in place with (4) 10mm screws. You'll also see 2 white nylon 10mm screws at the top of the cluster that hold the wiring connectors in place to the back of the cluster. Unscrew those and gently remove the cluster.
The entire dash after all that. It's very heavy on the PS due to the gigantic airbag on that side.
Along the way of removing the console, stereo, etc. you'll be disconnecting a lot of connectors. Take your time and don't break them!
Lower the steering column using the 14mm socket. There are 4 nuts that hold it in place. Once it's dropped, you can move it around easily.
Below the dash you see Space-Shuttle level wiring and a huge steel bar that is the main support that everything mounts to. All of the connectors are unique, so you can't cross-connect anything. You'll also see 4 black plastic air ducts that feed the dash ducts. They just unclip and also have a couple screws that hold them in place.
There is a plug in the PS A-Pillar for the airbag. Disconnect that. You'll have to unhook that bar (it's mounted on locating pins) and swing that bar out on the PS. So, the bar will be at a diagonal like the picture in that Lexus Forums link I posted.
That steel bar will need to have the bolts removed from the outside of the body, below the A-pillars. There are 4 black body grommets that once removed, you can get a 12mm socket into. There are also 2 vertical bars welded to it on either side of where the stereo sits, that go down to the floor. There you'll see 2 nuts on studs that you'll have to remove. There is also one bolt directly behind where the instrument cluster was that attaches the bar to the firewall. Remove that. Once all the bolts and 2 nuts are removed, you can unhook it from the locator pins and swing it out of the way. Get a helper, it's heavy. Be gentle. The main wiring harness is attached to the bar and you don't want to mess up any of the wires. When you sit the bar aside, make sure that those 2 vertical spars aren't resting on any wiring on the tunnel, as well.
Use the 4mm allen wrench to remove the AC lines from the expansion valve you'll see located on the PS of the HVAC box, at the top. Once everything is moved out far enough and you have removed the blower motor portion off the HVAC box, you can remove the box, put it on the bench and open it up to swap the core(s).
The 2 cores sit about 3" from one another in the HVAC box. The heater core lines enter the cab from the DS and the evap core lines enter in from the PS. To change either one, or both, the entire HVAC box must be removed. It's quite large, and it must be opened up on a bench to swap the cores.
The HVAC box itself is a bit of a puzzle. It's comprised of 3 sections. 2 outer sections, like clamshells and a thinner, center section. It's held together by about 8 phillips screws right down the center, around the entire perimeter of the box. You'll have to manipulate the vanes in the box in order to separate it and once the core is in, manipulate them all separately, while lining up the vanes themselves so the box all goes back together smoothly. If you remove any of the actuator servos, make sure you place the vanes back on the actuator tracks properly.
At this point, you'll want to take your time and start reassembling the truck in the opposite order. Check, double-check and triple check all the connectors and wires.
I ran into trouble at some point and had problems upon startup. The truck started and ran, allowing me to refill and burp the cooling system. But, the gauges didn't work. The cluster lit up, and had all sorts of error lights on it illuminated. My center diff was also locked so I couldn't drive it. I had it towed to the dealership since I had 3 1/2 days into this project so far and I couldn't do any more.
They found that the one connector under the center console that I couldn't find a mate for was responsible for the center diff being locked. The gauge problem was attributed to one of the large connectors behind the stereo had gotten pulled slightly, pulling some pins enough so that the gauge cluster wasn't receiving signals. Luckily, the tech found it in a few hours.
They also evacuated and recharged the AC. The total bill wasn't too bad and was well worth it to me to have them finish the job. They also gave me a new RX350 as a loaner for the day!
Short story long, looking back, I saved some money by doing it myself. However, absolutely everything has to go right and not one thing can go wrong. I don't know if I'd ever attempt it again. In my opinion, it was hellish. My body is still sore but it's finally over!
Hopefully this helps others in the future and can serve as a cautionary tale! If you have any questions, just ask.
