I'm in the middle of replacing the heater core on my 94 GXE.
QUESTIONS: Does the big brace have to come out? Someone in here said they were able slip the heater box under it but I don't see how. I'm afraid some wires will get yanked if I remove the brace and can't support the steering column. There's also a lot of stuff attached to that brace that makes it look difficult to keep everything sorted out. Any advice will help. thanks.
ANSWERS TO MY OWN QUESTIONS: yes, the big brace must come out. No, you can't take out the heater box without removing the brace. Let the steering wheel rest on the drivers seat.

 

Pretty sure you have to take it out. I'd remove it leaving as many things bolted up as possible. Don't be discouraged by the wire connectors, it's not too hard figuring out what plugs in where, take pictures and label connectors if needed.

 

AHHH, the evil tamper proof torx will come off with little lockjaw pliers (aka visegrip)

 

just go to a hardware store or something and they should have a torx security set for like 20 bucks. last time i bought a set for work a kit with around 30 torx and security sockets was 10 bucks

 

They don't have them, Napa should.

1/4" kit? Not gonna work. It's a much larger bit.

 

3/8" torx are cheap too, i remember the last set i got with big torx was under 20 bucks

 

Just remember to disconnect the battery before screwing with the airbag stuff if you haven't already!

 

Yes, I disconnected way before I started pull wires apart, etc. I'm down to the heater & a/c box- almost there! Spent ~8 hours so far. Rad has been drained and hoses disconnected.
I know someone explained how to swing the heater box out to access the core, I just don't remember the post.
Can someone describe what screws/nuts and linkage I have to remove to swing out the heater box to slide out the core?

FWIW: I did not remove the seats as I used the drivers seat to support the steering column and gave me a place to sit while working. I'm in my mid 50's and have some spine issues so to you guys who have back issues, be careful doing this job as there is lots of twisting involved and you could hurt yourself. Once your into the job, there's pretty much no turning back.

 

Here's dash photo of everything stripped away and ready to remove heater box to access the heater core.

 

Here's a closeup of the climatecontrol unit before I extract all mounting screws and loosen up the a/c line bracket under the hood.

 

I have all the nuts and bolts removed that mount all 3 climate control units to firewall. I loosened up the return a/c line bracket (big line that has insulation on it) in engine bay.
I still can't pull the a/c box far enough away from the firewall to allow the heater box to release and swing away from the a/c box.
?Question: Do I have to disconnect the a/c return line under the hood thereby releasing all my refrigerant? That would give enough play to the a/c box to move away from firewall.

 

Finally got the heater separated from the a/c box. Loosened up the a/c suction line bracket under the hood that is near the right strut tower so it allows the a/c line some slack so I could yank on the a/c box inside. Yes, you have to yank on it pretty hard to get the heater box to separate. The problem here is the heater box has a flange on the backside against the firewall that stops you from pulling it forward if you don't have the a/c box angled out of the way. Once you get all the mounting bolts off just start pulling and it will eventually move enough to get that back flange to clear. I took out the heater box and rinsed it with water to get all the anti-freeze out and vacuum as much dirt as possible.
I noticed the heater core didn't flow very easily when I filled it with water to see where the leak is. I'm thinking that was what was causing the gurgling noise before it started leaking. I think the leak started around one of the seams where the tubes meet the plenum. Now time to get the new core and put it all back together.

 

HEATER CORE ALERT!!!!: If you order a new heater core for the 3rd gen Maxima, MAKE SURE YOU GET THE CORRECT TUBE SIZE! I ordered one for my 94 GXE from Courtesy Nissan and received a core with the 5/8" (16mm) inlet/outlet tubes. THIS DOES NOT WORK W/ MY MAXIMA! Mine has all 3/4"o.d. heater hoses. I also remember my old 1990 GXE also had 3/4" hoses. I cannot find any aftermarket heater cores with 3/4" tubes and Nissan says part# B7140-85E00 is the correct # for my VIN. Sooo, I leaning toward reinstalling the old tubes with new O-rings and I've made sure the tube n/pples are not cracking apart due to age.

Here's my current plan: I will reinstall the old tubes with new O rings and sealant, leak test the core with my air compressor set on Low. Then, reassemble the heater box. Courtesy Nissan guys said I can refill coolant and start the engine even tho all the dashboard guts are gone and check for leaks. That's a great idea so hopefully it will start and heat up to do an in-place leak check.
UPDATE: I went to Carters Salvage in Plano/Allen TX and saw a bunch of 3rd & 4th gen Max's + I30 + Quest minivans that all had 3/4" heater hoses. Only saw 1 90Max GXE that had 5/8" hoses. Most of the Sentras had 5/8 hoses. Courtesy Parts is looking into why I received the 5/8" tubed core.

 

I did the in-place leak test by warming up the engine and running coolant into my new core from Autozone using the old tubes.
One tube has a pin-hole leak where they electro-weld a little closure cap on the tube during manufacturing. Now I'm in a tight spot. Using 20 year old nylon tubes is not a good idea even if the leaks are sealed. It just means there could be more leaks to develop on this part as the plastic ages and breaks down further.
If I can't get Nissan to send the core w/ the correct 3/4" tubes, then my options are to use the incorrect Nissan core and do a heater hose conversion from the 5/8" core tubes to the native 3/4" on my car. This will lead to some funky plumbing under the hood.
Or, I can reuse the old tubes after repairing the pin-hole leak with super-glue and Scotch 800 sealant and hope it lasts. This idea just sounds way too risky since my life usually follows Murphy's Law.

NEW UPDATE FROM NISSAN: NISSAN NO LONGER OFFERS A 3RD GEN HEATER CORE WITH 3/4" TUBES. THEY ARE ALL 5/8" dia. TUBES. TIME TO GET CREATIVE!

 

I finished the dash reassembly and restarted the car. Ran great w/ good heat. Still had to burp it w/ the front end up in the air. I only raised it about 15-18" on one of those little floor jacks and got most of the air out after running for almost 30 mins.

LESSONS LEARNED: Take photos of as many screws as possible. Don't use the iphone camera, use a decent point-n-shoot digital camera for better resolution and stronger flash. Photograph each time you remove a piece and let a wire dangle. That way you'll know how the wires route behind the dash. I used a muffin pan to keep all the screws sorted out. Wash out all the ductwork and you'll have a clean smelling system! The carpet in floorboards are waterproof so you can flood it and then suck up all the coolant that leaked out with a wet-vac. Water will not penetrate through the carpet into the floorboards. If you need a 5/8" to 3/4" hose converter, brass PEX plumbing fittings work great and are not as long as plastic automotive connectors.
Now if my back will just stop hurting!!

 

Thanks for your write up I plan on following it in the coming weeks on my se