A/C issue (BMW E82 content)

I'm aware that the A/C in my 128i has a very tiny leak somewhere. I had it serviced last fall with a pro machine. It held vacuum without loss for 15 minutes or so, so whatever leak there is is really small. When I went to use the A/C a couple days ago, of course, it's not blowing cold. OK, fine. Checked low side with crappy gauge: no pressure. Checked high side with scan tool: 1.5bar. Obviously the refrigerant is gone.

Here's where it gets odd. I had a small can of R134a on the shelf (340g; capacity is 590g), so I figured I'd throw it in to hold me for a few days of commuting until I can get to the shop. The system won't take a charge. Can is punctured, hose is connected, but the can never gets cold or lighter. After a good 15 minutes connected with the A/C on max I finally saw the high side tick up to a peak of 5bar via the scanner, but that's still way below anything meaningful, and doesn't really address the problem.

I checked all the temp sensors in the system and they're reading properly, so it should be calling for A/C. The compressor is engaged. So what's not working that I can't get refrigerant into the system?

If it's a constant-run compressor, you may have destroyed it by driving the car without refrigerant.  The usual failure mode is seizing up rather than failing to compress, though.

"Holds vacuum for 15min" isn't much of an assessment unless you are using a microns gauge, which is a really awesome tool that I'd love to have...

Well, the compressor is clutchless (it uses a swash plate, apparently, at least according to Bentley). Does this type of compressor not have some sort of low pressure safety switch to keep it from self-destructing? I mean, if I can read the high side pressure electronically through the scanner, surely the computer doesn't ignore this if the system is discharged.

I don't know what sort of gauge they used, though it is part of a pretty fancy all-digital, fully automated rig.

I really dislike working on A/C systems, and if I could live without it I would, but a black car, a hot day, and dress clothes don't mix well without it.

If it's clutchless, it's turning all the time.  The oil circulates with the refrigerant, and when you lose refrigerant, you lose oil.  Newer compressors are better about keeping the oil trapped in the compressor (the outlets have oil separator like geometry to them) but if there's no refrigerant moving, there's no oil moving either.

Can't hurt to pull it under a vacuum and try to recharge it correctly, the worst that would happen is that you're out the price of the service in addition to the other repairs you'd need to do.  It might just be so low that the H-block isn't functioning properly yet.  (Assuming that these use them - I know the X3s do, since the little valve makes a hellacious humming noise if the refrigerant is even a quarter pound low)

I'm going to try to pass by the shop on Tuesday. Unfortunately that does nothing for me tomorrow, but I don't have the equipment nor (after fighting with the Saab for the last two days) the energy to do much beyond what I've already tried. Just trying to anticipate what might have failed and what I should expect to get it working again.

Just hope it's not the evap, that means pulling the dash.