I had to do some work on my A/C this week and found out a few more things about the system. I have a facelift and auto air so I have the compressor with the variable displacement valve. The compressors seem to look identical in the pics but have different part numbers. With the valve working properly it holds the low side to 40 ish PSI so the evaporator should never freeze (mine was prone to freezing because the regulator valve was stuck full on instead of "off" like others have had when they had no A/C.) The system with the variable displacement compressor also has a different evaporator temp sensor which does not touch the evaporator and measures the temp of the air that has already gone through so it can not turn off the compressor if the evaporator gets cold enough to start freezing which makes sense since the evaporator should never freeze and the goal of the variable displacement compressor is to not cycle. However there is an additional part number for an evaporator sensor "kit" which might be an adapter to use the non variable displacement sensor and prevent freezing if the compressor is stuck on full tilt. Just a guess on my part but I was thinking of doing exactly that at one point. It might have been tempting to do the change-up when the compressor was $1200 or the valve was not obtainable but the Nissens compressor seems to be top quality and under $300. The variable displacement valve is not all that easy to get and comes in different pressure settings and it seems that the X5 uses a different part number/pressure than anything else. I ordered the valve anyway since I spent so much time trying to find it and was curious so I might replace it in the old compressor at some point. If anyone has a seen a part number/pressure chart for the variable displacement valves that my be interesting as well.

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)