I bought my '85 318i as a beater, no ac, dead alternator etc.
Anyways, looks like the previous owner used one of those Wal-Mart "death kits" and ruined the system. To top off his idiocy, he left the suction lines off in the trunk so I had water and rust in my system
Tried reviving the old Bosch, died immediatly and shot rusty oil (PAG & Mineral mixed together!), and the chunks of elastomer from inside the compressor.
Here's how I fixed mine:
1 Reman. Bosch compressor from Autozone (says Ready Aire on box) $299
1 Expansion valve $39.99
1 Accumulator/drier $45.00
3 cans R134a $3.47 (straight 134a, NO additives like oil or "stop leak"
1 R134a retrofit kit (gauge hose and fittings, may come with o-rings too) ~$25.00
1 Bottle 8oz POE viscocity 100 oil (the pour-in kind)
1 Inline filter (optional)
Step 1: Replace expansion valve (note the gunk inside of it, that's what kills compressors)
Step 2: Replace accumulator/drier making sure to transfer all the old pressure switches from the old one to the new one.
Step 3: Remove old compressor. Add 6.25oz of the POE oil into the new compressors high side port, making sure to leave a small amount to pour in to the suction side as well. Turn the clutch clockwise rapidy (either by hand or with a socket) about ten times. Add the rest of the bottle to compensate for the new accumulator (total of 8oz in compressor)
Step 4: Reinstall new compressor. If O-rings are in bad shape replace them, otherwise lightly coat the O-rings with some POE oil and install the high side first and then the low side.
Step 5: Connect compressor clutch wire. Your stock compressor clutch wire will not plug into the new compressor. What I did was clip the end off of the old compressor and spliced it into the new one so that it would still have the same OEM type clip.
Step 6: Attach new r143a port fittings onto their respective sides (high/low)
Step 7: Turn car on and set A/C to the highest setting. Attach guage hose and can and begin charging. I used about 2 1/2 cans (until the high pressure switch would cut out and cycle the compressor, showing that the system had enough high side pressure). BMW spec calls for 36oz of R12, but since R134a is more efficient I calculated that ~32oz of R134a would provide the same cooling efficiency. DO NOT OVERCHARGE, high head pressure kills Bosch compressors.
Step 8: drive around and enjoy your spiffy el-cheapo a/c retrofit
Apparently Ready Aire rebuilds the Bosch units with a neoprene elastomer that does not disinegrate like the original rubber ones do.
It is absolutely imperative that you change the expansion valve and drier when you do this, because you lose cooling efficiency and it will starve the compressor of oil leading it to seize.
I am getting ~40-43F at the vents, and if I turn it up high enough I can see my breath it's so cold!