The air conditioning was blowing warm in 2002 and by 2010 I had removed the compressor from the system because its heavy and I am (was) a young guy and all, I could roll down the windows. So when the drivetrain came out in 2013, the dryer and lines went into the box with the compressor and was one more thing sitting on the shelf. Until two months ago, when I pulled the box off the shelf and dug out the new o-rings, and dryer that were purchased in the past few years. Threw it all back into the car (like a good completist would) with good intentions and naively hoped for the best. Of course it didn't blow cold. And not being an HVAC guy it was time for the learnings. The system held a good vacuum, and was taking and holding refrigerant, but the low side would dip into a vacuum once the compressor was spinning fast enough to compress (~1200rpm). Blocked expansion valve says the internet. Said valve lives deeply under the dash, and having never dug that deep, was reluctant.
Ordered the expansion valve and tore into the dash hoping to get it done in a day. And could have, but had ordered the 84 and up expansion valve, not the 82-83 valve. The good news was the evaporator box came out in one hour. A fine user Craig(93?) on this board walks through the basics of removal and some tips for reinstall so that really helped. The dash stayed in, the stereo fascia stayed in and the kick panel, glove box and shift console were removed. With the right expansion valve it all went together pretty smooth.
One of the challenges with the evap core is what to replace the disintegrating foam on the sides with. I ended up using strips of sound deadener, it should perform the air blocking task well.
The original expansion valve on the back side of the evaporator. When you finally get to the valve you realize how small the orifices are that the refrigerant flows through. In my case, I'm pretty sure the valve had rusted itself shut.
There's insulation applied to the outside of the fan cage from the factory that was coming off, I replaced it with foil backed sound deadener. If done again, I wouldn't run the foil quite so high up the front as its slightly visible from inside the car.
Evap box was pretty clean for 33+ years old. The blower motor has seen light duty over the years and was lubricated and put back in, it sits in the front here.
The original insulation on the inlet pipes for the evaporator. Whatever its unique makeup is, it smells bad, and was definitely the source of a rare unpleasant musty smell.
Replacing the factory insulation with rope caulk. MyE28 provided this tip, and it just so happened that I had a box of rope caulk sitting around. It took me a while to understand the insulation purposes here, (other than keeping the refrigerant cold) and its this, you want to prevent humid air from condensing on the cold inlet pipe. To do this you ideally have a 100% seal on the line.
Also used the foil backed sound deadener to close the openings in the evap box, which worked pretty slick.
Dum Dum Strip caulk. Once the evap box was back in the car the line including the fitting is completely wrapped as the factory did.
Once the car had its new exp valve a vacuum was drawn on it for the second time, which held nicely, then added R12a refrigerant. Yes, the propane/butane refrigerant. It works fine but received damning push back from a few shops. Whatever, the R12A is a superior option imo for original, old school R12 systems. If leaked to atmosphere it breaks down to carbon dioxide and water quickly and it creates less head pressure on the system which is good if you're using the original hoses (I am). And it blows cold, which is subjective, so I picked up a thermometer in Thousand Oaks CA in August and sampled the vent temps under various conditions. The gist, it can blow 32.7F on a 75F day. And will blow ~44-48F at 65mph on a 104F day IF the fresh air vent is closed.
The original compressor was degreased a few years ago and works fine. Kind of? The system operates as intended but at 1500rpm (only 1500rpm) it can growl pretty significantly inside the cabin. Quiet under the hood at 1500rpm, so -maybe- its just the expansion valve doing its thing -dunno. But the a/c growls at 1500rpm, sounds like bad bearings, you don't hear it under the hood, and it blows cold which is great. So we'll chalk that up as a -1 on the NVH and leave it alone.
I received a good tip from the second HVAC fella who helped me out. Use dielectric grease to lubricate the o-rings. When assembling the system I had wanted to lubricate the o-rings but didn't as the only advice I read was to use mineral oil itself, which I didn't have. I did have dielectric grease though, next time.
And here's my E28 a/c tip that proves I'm not an E28 a/c guy. Close the fresh air flap (the middle slider) to get colder air from the a/c at highway speeds. I was wondering why the a/c was less effective at highway speeds and was filing it under old car, old a/c, maybe a weak compressor. Until
after I left the deserts of California and realized that I could drop the vent temps by 10-15F (on a hot day) at highway speeds by closing the fresh air flap. Makes perfect sense, especially if you examine the way the weighted flaps are set up that control which source of air can use the center vents.
The fresh air/air conditioning diverter with the weighted flaps sits on top of the evap box and fell off as the box was being removed. You can see one flap is askew, the pivot setup for these flaps is certainly fragile. It was reassembled in this case and works properly, but is still fragile and I could see having to get creative for a lasting repair next time its out.
Lastly, my favourite lines on an E28. Highway speeds + rain + distance = these road grime tracks. And they consistently look like this. Neat. Dirty, but neat.
Get off my lawn old man time 
Shit happens. Hence the build thread. 
(Pixel attempt via a Motorola fliphone)
