A puzzle: how to remove the heater blower box?

[JBStories]

I've been away from my X and this forum for a few months but now have decided to tackle replacing a leaky heater control valve and/or heater core. I have some awesome new carpet and upholstery from Henk to install so now I'm motivated to stop the coolant drip on the floorboard!

But I am perplexed beyond belief at how challenging it is to remove the lower heater box. I've seen a thread or two about it being difficult (like this one: https://xwebforums.com/forum/index....-a-heater-fan-blower-issue.31539/#post-264951). But it's still not coming out.

On my 1981 with AC this is now completely disconnected, hoses off, clips off, and is loose enough it should just slide out. But the plastic blower wheel is in the way. It is pretty flexible, but I'm afraid of bending it too much and it cracking. Anyone have any advice?

Driver Side:


Passenger Side:

 

[LarryC]

Well, as you saw with that thread, the answer is: AC-heater box removal. I too wish someone would have a brainstorm because after all that (having my heater blower motor rebuilt) the heater blower motor on my X is acting up again. And I am desperate not to go through the removal of the whole AC-Heater box again. But as of this moment that appears to be the only way. If we say this loudly enough maybe someone will show us the way. I have not found the way. But having said that, while you are at this stage, please feel free to explore all options and report back. It is so close.

Incidentally, my AC-Heater box rebuild thread: https://xwebforums.com/forum/index.php?threads/ac_heater-box-rebuild.20043/

 

[Dr.Jeff]

Unfortunately JB, I can't offer any answers. But I'm watching this because I will need to pull my late model (with AC) heater box eventually. And it looks like the old threads on this topic are either gone or suffer the PhotoBucket plague.

after all that (having my heater blower motor rebuilt) the heater blower motor on my X is acting up again.

Larry, I don't recall. Did you rebuild the actual motor yourself, replace it with a rebuilt motor, replace it with a new motor, or ??

 

[lookforjoe]

Nobody has cut the end off (pass side) & slid the core out? I'd consider than an option before dismantling the entire dash... I can't find any reference of this being tried. Seems an obvious way to deal with the issue. Cutting it doesn't automatically mean a shitty repair, although I have seen many of those on Volvo 240 series blower motor replacements...

I've not seen pics of the INSIDE of the bare box to determine if that is feasible (inner obstructions, etc..).

End cap could be plastic welded, abs-cemented, etc., back in place if cut carefully. My approach would typically be get a spare box & hack it up to make a replacement end cap..

EDIT: if this is accurate, don't see why that wouldn't work

 

[LarryC]

Dr Jeff, no I sent it out to have it "rebuilt" at considerable cost. I am thinking that no one who claims to rebuild electric motors really does. BY rebuilt, I mean the bearing surfaces. They all just do windings and such. They just lube the bearings and call it a day.Six months later your electric motor is squalling to beat the band. It is and always has been about the bearings.I am not sure why this is not apparent, but apparently not. I figured a new old unit would suffer the same fate sooner or later and wanted to avoid that at all costs. It looks like you can't.
Hussein, yes that would work... for the heater core provided one had the skills to do a good repair on the housing. Most don't. In any case, it would not help with the blower motor.
Removal of the dash is not only not necessary it does not help. The restriction is the lateral opening.

 

[Dr.Jeff]

I sent it out to have it "rebuilt" at considerable cost.

That really sucks, but I know exactly what you mean about not getting what you expect to be done.
In the past I've tried to revive an old motor by cleaning, adjusting, and lubing everything. It helps considerably initially, but like you said it is only a temporary 'fix'. Given the cost of replacement motors (if they are even available) I wonder if someone could provide a service to modify it and replace the bushings/bearings with sealed ball-bearing units.
I'm so not looking forward to this job. For some reason dash related work always seems to be a real pain.

 

[JBStories]

Sadly I think all of you have confirmed what the Fiat service manual says on page 50-16: "A/C-heater unit must be removed to remove evaporator, blower assembly and water valve." I suppose in the end I will be happy I did this so i can thoroughly R&R the unit, clean up any crud, and fix some seals. But it's amazing how painful this is going to be! In my case, I know my A/C has zero R12 charge so no worries there. I now need to pull up the AC retrofit posts and see what I would need to do NOW so that IF I decide later I want to do that project I don't have to pull this thing out again.

(The idea of cutting the plastic housing is very creative. But I have bad luck working with plastic!)

Ugh

 

[PaulD]

Sadly I think all of you have confirmed what the Fiat service manual says on page 50-16: "A/C-heater unit must be removed to remove evaporator, blower assembly and water valve." I suppose in the end I will be happy I did this so i can thoroughly R&R the unit, clean up any crud, and fix some seals. But it's amazing how painful this is going to be! In my case, I know my A/C has zero R12 charge so no worries there. I now need to pull up the AC retrofit posts and see what I would need to do NOW so that IF I decide later I want to do that project I don't have to pull this thing out again.

(The idea of cutting the plastic housing is very creative. But I have bad luck working with plastic!)

Ugh

When I did mine, someone posted that it is like giving birth to a baby. I am sure that almost all women would disagree with that vehemently, it it a close fit though. As I remember when the top nuts that hold it in are off and you have to drop it an inch before working it out the right side, I also remember it helped to wiggle it and clear the bolts on one side first (the right I think). This was a number of years ago, I am probably remembering wrong.

On putting it back in, remember to attach the ducts going to the dash vents first. I had to take it out again to attach those. The second time out was easier though. Check everything, one of my vents was rusted shut. and the foam seals were turning to dust.

Paul

 

[LarryC]

One final thought and long shot. Could one separate the middle and lower housings from the upper housing and remove just the lower two housings? Those two are where the heater core and blower motors live. That would avoid the need to unhook the AC lines and other nastiness associated with the upper housing. You would still need to deal with the connections for the heater valve, but that is minor by comparison. Except for the exiting hard lines on the passenger side of the upper housing, the bottom of the upper housing is free of protruding things. I think I know the answer, but I have not tried that and wanted to throw that out there. Like I said I too am desperate not to remove the whole box again.

 

[JBStories]

Well, I finally got it out! After leaving it alone most of the winter in total disgust and frustration I decided yesterday to approach my half started project again. I took my time and saw that it was partially hung up on a wire on the right side. After separating the top most housing with clips I suddenly had enough clearance to remove the beast, although the top housing was still "connected" by the metal arm coming from the vacuum motor. Part of the challenge as I think about it was that the X's fuse box and wiring isn't exactly neat and tight. After having to work on or diagnose so many electrical issues and doing the brown wire mod I think that whole part of the footwell has more bulk. You have to remove the box and shove it to the front right of the well to make room for the heater/AC box so this just makes it a tight job. Here is a photo of it as it sat most of the winter:



Now, the real challenge is fixing this thing. I have zero desire to get the AC working but need to replace a bad radiator and water control valve on the back. That little water valve seems to be impossible to find these days. I need to do some more searching on the forum for ideas. Maybe I can just rebuild it...

 

[Dr.Jeff]

JB, a few thoughts on this project.

Although I have not tackled this job yet (but I need to), I think removing the entire box is actually worth while. Because that will allow you to give it a good cleaning and freshening of the seals, etc, in addition to the repairs you have planned. When I pulled the box out of a same age VW Caddy, inside I found a ton of toxic crud built up everywhere. Professionally speaking it is a health hazard, so worth cleaning it out. And getting all of the moving parts to function freely and sealing all them will make it work much better.

Did splitting the upper half make the difference in getting it out? Please tell me a little more advice on removing the box.

For the heater valve, the A/C version is difficult to find. There was a prior discussion that identified possible universal valves that can be used. Take a look: https://xwebforums.com/forum/index....-control-valve-replacement.27435/#post-228926

Even though you don't seem that interested in restoring the AC portion, this is an excellent time to do that. However be advised to do it right (converting from R12) there is a lot involved. You should replace all of the O-ring seals (with the type for R134a), all flex-hoses (the walls retain a lot of old R12 within them, plus they will be old and leaky), flush the evap and possibly replace the expansion valve. If the old system suffered a failure then the compressor might be bad and the condenser contaminated (a great time to replace it with a high-efficiency condenser). So it is a big job, but to do anything less will be a waste of money because it will fail again and ruin any new parts in the process.

 

[lookforjoe]

I would consider an external inline heater valve, there are a number of generic options, or even elaborate ones like Vintage Air offerings with electric solenoid control (that's my likely choice).

Even though you don't seem that interested in restoring the AC portion, this is an excellent time to do that. However be advised to do it right (converting from R12) there is a lot involved. You should replace all of the O-ring seals (with the type for R134a), all flex-hoses (the walls retain a lot of old R12 within them, plus they will be old and leaky), flush the evap and possibly replace the expansion valve. If the old system suffered a failure then the compressor might be bad and the condenser contaminated (a great time to replace it with a high-efficiency condenser). So it is a big job, but to do anything less will be a waste of money because it will fail again and ruin any new parts in the process.

If the AC is being fixed, the receiver/dryer and expansion valve would be the prime candidates. There is no orifice tube or accumulator, so the aforementioned items are what need to be replaced on a system left open/under refurbishment. Although oring replacement is ideal, it doesn't have to happen, neither do the hoses. I converted many a Volvo back in the day, and the only essential item was the receiver/dryer, proper refrigerant oil & the R134a fitting. The X1/9 system is identical to that old Volvo 240 series setup. If the system holds vacuum after replacing those items during the pre-charge process, there is no reason to dig deeper. Those AC lines would be a nightmare to replace, unless you're going for a complete LarryC style overhaul I don't see the point.

 

[Dr.Jeff]

Yes, thank you I completely neglected to mention the receiver/dryer...the "filter" of the system, important to replace.

The expansion valve has the same function as a orifice tube and needs to be cleaned or replaced for the same reason; it has a small hole through which the refrigerant passes and clogs easily. And the receiver/dryer has the same function as a accumulator, so in effect these systems do have those components.

Based on how I interpreted the comment "I have zero desire to get the AC working", I assumed it was a non-functioning system in need of refurbishment and not simply a refrigerant swap. Typically older systems like these have had a compressor failure (although not always), so the system has been contaminated with debris from the failed compressor, as well as any exposure to the atmosphere (also common for an older non-functioning system to have been disconnected and left open). However replacing hoses, O-rings and the other components noted, plus flushing the remaining items, is considered part of a proper refrigerant change-over regardless. Agreed you might get away without some of it if the system is still functional and serviceable, depending on the status of the parts. But the service recommendations by the AC manufacturers and professionals is to replace them. That's one of the few benefits to my current (temporary) living situation in this extreme desert climate, it has a ton of top AC experts to consult with and is a popular location for AC seminars.

As you say, replacing the hoses on the X is a huge task. However their length and exposure makes them susceptible to becoming dry and brittle, leading to leakage through the walls...in addition to the inner surface being saturated with old refrigerant and oil. I intend to re-route mine and eliminate most of the hard lines, connections, various external switch ports and valves. Converting it to a more modern type arrangement with a trinary switch on the receiver/dryer.

 

[JBStories]

Jeff - I wish I could be precise on how I got it out. The only "trick" was to pivot it down and to the right passenger footwell enough that it was possible to take off the top most housing clips. There is a control arm that I had to remove (single screw) to free it up entirely, but this was pretty easy. Without the top part of the box it was possible to maneuver the rest up a little to clear the framing of the dash/console. The REAL question is how I will get it back in!!

The link to the heater control valve mod using the 4Seasons part is excellent. Thanks a lot for posting that. I already located a Ranco H28 type valve on eBay earlier today and bought it. It's not an exact match to the OEM (also a Ranco H28, but different subtype). However, my plan was to separate the "new" valve from the bracket housing and reuse my stock housing. At least this was my plan. I will have to see which option works better. Something tells me the 4Seasons valve will perform better than a NOS item that has sat for 20+ years.

Here is the not-quite-a-match Ranco valve I found:

By the way, does anyone recommend specific foam I can get in sheets or pads for the heater box rebuild? There are several places where old foam provided a seal on vent doors or around cabin ductwork. This is lightweight stuff. There is also some denser foam around the side of the heater core and also surrounding the evaporator coil.

The A/C situation is more complex. I have a passable knowledge of split A/C systems, a set of gauges, and even an EPA cert so I can handle refrigerant. But everything about the X1/9 system looks like it will annoy the hell out of me. Lots of tight spaces. Routing new hoses front to back (I just have to believe they are rotten.) Finding someone to make the new hoses and fittings. I simply don't have the appetite or time to tackle it, although it would be amazing to have it. The system was empty when I got the car after it sat untouched for 12 years. No clue what specific component failed, but the truth is the only way I would do it would be to start over with new components. Maybe one day.

 

[Dr.Jeff]

Back when that link on the replacement heater valve came out, I looked for the specific part number mentioned but did not find any available. So the one you got is likely the best option. It should work fine, stick to your plan.

For insulation material, look at some closed-cell foam. It is kind of like wet-suit neoprene rather than foam rubber. It lasts longer, insulates better, and a thin layer with self adhesive backing can be used (easy to work with). I've seen it with a reflective silver layer on one side but don't really think that's necessary. Maybe search online.

Ya, the X's A/C system design isn't very good at all. I live where A/C is absolutely mandatory so I have to rebuild mine. I am replacing everything but the evaporator (flushing it). To make the hoses I will buy some bulk lengths of the correct diameters and cut them to length as they are laid out in the car. A local shop will crimp the fittings where I clock them. I don't plan to run the hoses the same way as the factory and I don't plan to use any of the original pressure switches, fittings, etc. The evap box will remain basically the same (just rebuilt) and the compressor mounts will be the same, but everything else redone. Big job but should be worth the results.

 

[JBStories]

I'm still working on this problem. Here is an update. First, the replacement Ranco valve I found on eBay won't work. The post that operates the piston is just too long. So I have decided to replicate the replacement posted by drsnemann (https://xwebforums.com/forum/index.php?threads/1986-heater-control-valve-replacement.27435/) This uses the 4Season valve which is readily available, but the tricky parts are mounting it to the box, making a lever that works, and rerouting/securing the cable. I'm not finished with this yet, but here are some photos of progress so far. I'm a little worried the lever is too long and so am in the process of removing the control cable from the car so I can test it. Worst case I'll redesign the lever. I am really hoping I can keep the stock cable attach point so that it is easy to attach/detach under the dash.

#1 - The stock 4Seasons valve.

#2 - My replacement lever, using the swivel connect point from the original valve attached to a piece of metal with pop rivets. I filed the hole to match the valve's odd-shaped connector. The gray metal piece is bent slightly to allow it to clear the frame of the existing bracket when it rotates. Finally, I ground the pop rivets flush on the reverse side, again for clearance.

#3 - The bracket to attach to the heater box.

 

[Dr.Jeff]

I'm waking up this sleeping thread to add my current experience to it. I would like to see the title of this thread revised to state it is about the "AC" style box, and not the much more common non-AC one. For reference, there are a couple of other threads that are related but did not seem to offer much help. Of the existing threads I could find on the subject this one seems best. So I'll add to it.

I just removed the AC style heater box from a '79. The interior was already partially stripped - carpet, dash, odds and ends. But honestly I don't think it is necessary to do any of that when removing the heater box. I can see where it will help to loosen the fuse box and move it as far out of the way as possible for more access (mine is still fully connected to the electrical harnesses, I just unclipped the box from its mounts).

The short version is I think the best approach is what @JBStories ended up doing - leave the top most section of the box in place (do not loosen the four retaining nuts), and separate the middle section from that top section...keeping the bottom portion still fully connected to the middle section.

But to get there there are several little things that need to be done first. Not necessarily in this order:
1) Disconnect all THREE heater hoses. The third one is completely hidden behind the box and it is easy to think there are only two hoses - like pretty much every other heater box out there. For me it was easier to completely remove those hoses. That allows more room to move the box out through the passenger's side.
2) Similarly I found it easier to disconnect the AC hoses in order to get them out of the way. But technically they attach to the top portion of the box, so maybe you could leave them on? One additional note here: one of the evaporator fittings hung down too low to allow the heater box to come out. I had to bend it up about an inch to make enough room. That will be more difficult to do with the hose still connected to it. However some cars may not have this issue if the fitting is already out of the way.
3) Disconnect the vacuum module that actuates one of the air flow "doors" in the upper portion. It is on the drivers side and difficult to get to. I found it easier to drill out the two rivets that hold the module onto the box and leave the rest of it connected. Otherwise you need to get completely behind the box to unhook it. Be careful, the plastic arm on this module breaks easily, and replacements are not available. [ Correction, the arm is metal not plastic. See my comments in post #18.
4) Disconnect the electrical connector to the blower motor. ]
5) Disconnect the cable from the control panel to the heater valve. I found it easier to disconnect it from the control panel and leave the other end still attached to the valve. But in my case the control panel was already loose so that was easy to reach. Otherwise you will need to get behind the box to disconnect the valve. Much like the vacuum actuator module it isn't easy to reach the connection.
6) I removed the three phillips screws that hold the air duct onto the face of the heater box middle section. That allowed the air duct to come off and free up the middle section so it can move to the side when the time comes. I'll have to go back out and look again, but this might only be possible with the dash removed. So that would be a major issue. [ Note: see additional comments in my next post, #18. ]
7) Unbolt the fiber optic main connection from the center tunnel. This gets it out of the way so the box won't get hung up on it when attempting its removal.
8) Resist the temptation to undo the clips that hold the lower portion of the box to the middle portion.
9) Also resist the temptation to loosen the four nuts that hold the top portion of the box to the chassis.
10) The middle portion of the box may be difficult to separate from the upper portion. There is a thick foam-rubber seal between them that will be very stuck to both sections. Mine tore while attempting to get it free. But once you have the two bottom sections separated from the upper section then they should slide out toward the passenger side as a unit. Don't expect it to be easy, a lot of fiddling is needed.

I'm sure I've missed a few items. I will see if anything else stands out when I go back out to take another look.

So far that is all I've done. The upper portion of the box is still attached to the chassis. But it should be easy to remove; removing those four nuts that we left on earlier should be all that's required. I will also note that removing that top portion allows you to clean and reseal everything. The AC evaporator is in that part and it will be much easier to flush and test it when it's out of the car. As a side note I was quite surprised at how relatively clean this box is inside compared to any others I've ever seen (on all makes of cars). But then I remembered something; a while back when I was removing the carpet and padding I noticed the vacuum hose that supplies all of the AC controls had been completely occluded when assembled at the factory. This is a small rubber hose that runs along the center tunnel. One of the other attachments had been installed on top of it completely smashing it so no air could pass. Therefore I believe it's possible the AC system in this car was never used - it could not have worked properly without the controls. And the car was a desert car, so the heater would not have been used much either. Furthermore this was a very low mile original car in much better than average shape. Therefore it's possible the entire HVAC system was rarely operated, helping to keep it cleaner than normal.

Reinstalling the whole thing will be another task in itself. Frankly I'm not 100% sure how easy it will be to reattach some of the stuff that had to be removed. But I need to rebuild the entire box first, so that will come at another time. Hopefully I'll remember to post more then.

 

[Dr.Jeff]

Adding to my last post (#17).

I removed the upper portion of the box from the car. The four retaining nuts are all that's needed and it comes out easily. Although I'd like to know why those four studs are sooo long, requiring you to turn the nuts forever to remove them.

I also verified a couple of things and need to make a couple of corrections to my last post....

The arm on the vacuum module for the rear air flapper door is metal, not plastic as I stated. Due to all of the wire harnesses and other obstacles on the drivers side I could not see it well until it was out of the car; I seemed to recall it being plastic on a prior X, but perhaps that was another make of vehicle. Because I removed the whole module body from the heater box (rather than disconnect the arm from the lever, see item #3), it came out with the upper portion of the box. Now the retaining clip that secures the arm to the rod can easily be removed. My plan is to ditch all of the vacuum controls and convert this AC box to the manual controls found on a non-AC box. So this module will get replaced anyway.

The air vent that attached to the front face of the box (the one secured by three screws, discussed in item #6 earlier) is on the lower section of the box - not the middle section as I stated before. However it still needs to be removed before the box will slide out. The good news is the dash does not need to be removed to access those three retaining screws. But the center console does.

Another thing to mention is the condition of the upper section of the box, once it was removed. There was more debris on top of it than in the rest of the box. This makes sense, as the outside air comes in from the top and therefore debris does as well. But this also kind of supports my theory that this HVAC unit was rarely used. If the top air flapper had been opened then that debris would have fallen down into the lower sections of the box. But those areas were relatively clean as mentioned. There is no signs of the usual mold either, typical of AC systems that get used a lot. Another finding that may support this theory is the fact the heater pipes that run in the center tunnel were completely rotted out, suggesting the heater valve was rarely opened and little circulation went through the pipes. While the other aspects of the cooling system were not nearly as rusty.

By the way, even if you only need to remove the lower portions of the box - for example to replace the heater core or blower motor - I recommend you still take a minute to remove the top section as well. As I said, that's where the most debris will collect. And it will be health hazard to not clean all the garbage out. So this is the perfect time to take care of it, very easy to remove the top once the rest is out. Also, others have found the metal flapper door on the very top of the unit to be really rusted. So it may need some repairs anyway. Again, easy to do once the top portion is out.

Sorry no pictures. This job was difficult enough without stopping to think about a camera. I'd rank the removal of a AC heater box right up there with doing a pedal box. And that doesn't include reinstalling it yet.

 

[Dr.Jeff]

Today I disassembled the AC heater box to start cleaning and rebuilding.

Luckily, for the most part everything is in decent shape. A little cleaning (still amazed how clean this box was inside), reseal, and reassemble. Although there are a couple issues to resolve.

I notice the flapper doors on the top and rear need to be adjusted. These two doors are interconnected, so one opens as the other closes. But neither fully open or close with the current adjustment setting. These are what's controlled by the vacuum module that I'll be replacing with a cable. Furthermore there is a place on the connecting rod that hits the edge of the box, preventing it from moving more than a few millimeters anyway. That needs to be clearanced.

Unfortunately I discovered the heater core now has a tiny leak. It didn't when I had the car running and tested/evaluated everything a couple years ago - before the complete tear down process. I guess it must have been on the verge of leaking, and sitting a couple more years did it in. I'll have to revisit the thread where someone else was searching for a replacement to fit the AC style box.

I don't recall this being discussed before. There are some thick molded foam-rubber blocks inside the box that block air from going around the cores. I do not think they are available new, and frankly if they are I doubt they would be within my budget for this project. Mine have deteriorated in places but might be reusable. Perhaps coat them with a thin rubbery type layer - like spraying on "Plasticoat" or such? Here's what they look like:

The other foam seals are easy to replace with generic materials.

Here is another one of those funny "Fiat" design details. In another thread we discussed how the wire harness for the blower motor is pinched in the seam/joint between two portions of the box. Well on my '79 it's different; the wire harness passes through a hole in the rear of the box (pics below). Sadly the connector on the end will not fit through the hole, so the connector housing must be disassembled in order to remove the wires from the box:

Thankfully the blower motor works excellently and quietly. I was concerned because when it was still in the car it ran really slow in every "speed" setting - as many X blowers do. I posted this before, but when I removed the resistor pack ("firestarter" toaster unit) from the front scuttle cowl, I tested it. All three positions had significantly higher electrical resistance levels than indicated on the unit. I guess with age and use they build up more resistance. Therefore it acts to further reduce the current to the motor, and therefore the motor speed. So all of the "speeds" are MUCH slower than they should be. In other words, the problem is NOT the motor. I will replace the resistor pack with a modern one; either a circuit board style or a ceramic resistor style. The other option is to use a PWM board to control the motor speed. But I decided against that because I'd rather retain the stock controls.

I was planning to replace the stock heater valve with a VW style one. However my existing valve works good, so not sure if I will or not.

 

[Knubspud]

I'm waking up this sleeping thread to add my current experience to it. I would like to see the title of this thread revised to state it is about the "AC" style box, and not the much more common non-AC one. For reference, there are a couple of other threads that are related but did not seem to offer much help. Of the existing threads I could find on the subject this one seems best. So I'll add to it.

I just removed the AC style heater box from a '79. The interior was already partially stripped - carpet, dash, odds and ends. But honestly I don't think it is necessary to do any of that when removing the heater box. I can see where it will help to loosen the fuse box and move it as far out of the way as possible for more access (mine is still fully connected to the electrical harnesses, I just unclipped the box from its mounts).

The short version is I think the best approach is what @JBStories ended up doing - leave the top most section of the box in place (do not loosen the four retaining nuts), and separate the middle section from that top section...keeping the bottom portion still fully connected to the middle section.

But to get there there are several little things that need to be done first. Not necessarily in this order:
1) Disconnect all THREE heater hoses. The third one is completely hidden behind the box and it is easy to think there are only two hoses - like pretty much every other heater box out there. For me it was easier to completely remove those hoses. That allows more room to move the box out through the passenger's side.
2) Similarly I found it easier to disconnect the AC hoses in order to get them out of the way. But technically they attach to the top portion of the box, so maybe you could leave them on? One additional note here: one of the evaporator fittings hung down too low to allow the heater box to come out. I had to bend it up about an inch to make enough room. That will be more difficult to do with the hose still connected to it. However some cars may not have this issue if the fitting is already out of the way.
3) Disconnect the vacuum module that actuates one of the air flow "doors" in the upper portion. It is on the drivers side and difficult to get to. I found it easier to drill out the two rivets that hold the module onto the box and leave the rest of it connected. Otherwise you need to get completely behind the box to unhook it. Be careful, the plastic arm on this module breaks easily, and replacements are not available. [ Correction, the arm is metal not plastic. See my comments in post #18.
4) Disconnect the electrical connector to the blower motor. ]
5) Disconnect the cable from the control panel to the heater valve. I found it easier to disconnect it from the control panel and leave the other end still attached to the valve. But in my case the control panel was already loose so that was easy to reach. Otherwise you will need to get behind the box to disconnect the valve. Much like the vacuum actuator module it isn't easy to reach the connection.
6) I removed the three phillips screws that hold the air duct onto the face of the heater box middle section. That allowed the air duct to come off and free up the middle section so it can move to the side when the time comes. I'll have to go back out and look again, but this might only be possible with the dash removed. So that would be a major issue. [ Note: see additional comments in my next post, #18. ]
7) Unbolt the fiber optic main connection from the center tunnel. This gets it out of the way so the box won't get hung up on it when attempting its removal.
8) Resist the temptation to undo the clips that hold the lower portion of the box to the middle portion.
9) Also resist the temptation to loosen the four nuts that hold the top portion of the box to the chassis.
10) The middle portion of the box may be difficult to separate from the upper portion. There is a thick foam-rubber seal between them that will be very stuck to both sections. Mine tore while attempting to get it free. But once you have the two bottom sections separated from the upper section then they should slide out toward the passenger side as a unit. Don't expect it to be easy, a lot of fiddling is needed.

I'm sure I've missed a few items. I will see if anything else stands out when I go back out to take another look.

So far that is all I've done. The upper portion of the box is still attached to the chassis. But it should be easy to remove; removing those four nuts that we left on earlier should be all that's required. I will also note that removing that top portion allows you to clean and reseal everything. The AC evaporator is in that part and it will be much easier to flush and test it when it's out of the car. As a side note I was quite surprised at how relatively clean this box is inside compared to any others I've ever seen (on all makes of cars). But then I remembered something; a while back when I was removing the carpet and padding I noticed the vacuum hose that supplies all of the AC controls had been completely occluded when assembled at the factory. This is a small rubber hose that runs along the center tunnel. One of the other attachments had been installed on top of it completely smashing it so no air could pass. Therefore I believe it's possible the AC system in this car was never used - it could not have worked properly without the controls. And the car was a desert car, so the heater would not have been used much either. Furthermore this was a very low mile original car in much better than average shape. Therefore it's possible the entire HVAC system was rarely operated, helping to keep it cleaner than normal.

Reinstalling the whole thing will be another task in itself. Frankly I'm not 100% sure how easy it will be to reattach some of the stuff that had to be removed. But I need to rebuild the entire box first, so that will come at another time. Hopefully I'll remember to post more then.

Super helpful. Thanks! I got it out.