I'm still baffled. I suspect that Stevbfl is probably right (that's why I returned the rebuilt compressor last fall), but the guy who rebuilt it claims to have done 400 (personally) without problems since then, and he had started and sold a huge company that does rebuilds, so he knows a lot more than I do. And, the dealer tech didn't point at the compressor when he had the chance.

I looked at it again today. My assumption was that the system worked for a few minutes earlier this week, and since almost every part has been replaced (by me, most recently), I must have done something wrong and caused a leak somewhere. I had washed the major areas with Engine Brite before I took it to the dealer, and hadn't seen anything too scary, but I figured I would just pour 134a in the high side, with the engine off, and then try to force a leak somewhere. Put about 30 ounces in. High side up to about 130. The hub spins, so the pressure sensor apparently doesn't think there's too much refrigerant in there.

The hub spins, but there doesn't seem to be compression (even though for a few seconds, I thought I heard something laboring, and the high side pressure did read about 5 psi higher than the low, which is progress). No change in temperature at the vent. No dye in the driver's side evaporator case drain. Nothing new at the expansion valve (as best I can see). Compressor and drier look good, as do the hoses. I partially disassembled the front to look at both sides of the condenser, and it looks ok.

If nothing's leaking, I must have about twice the amount of 134a in there as I should. When the tech recovered the 134a lat week, he said he got about .7 lb., which is much less than I thought I put in there.

Something I don't understand is this idea of charging the high side. I repaired a 96 C280, with an identical Nippondenso 7SB16 compressor last year, and charging on the low side with the system running worked out just fine.

Last weekend, suspecting the compressor, I decided to swap the original back in. Unfortunately, I had pulled the control valve from it and I didn't reinstall it successfully ( didn't have the right replacement seals, so I reused the originals, and I didn't know how to adjust the screw - if anyone can tell me how to do this, I'm all ears). The system held vacuum for a while, but when I tried to do a partial charge the control valve leaked, and I didn't get anywhere.

I hate the idea of having the refrigerant recaptured again, and trying another compressor. Should I take it back to the dealer - is there an obvious next step for the tech there to try next? How would they diagnose a bad compressor?