Intermittent AC - out of ideas

[FellowsheepTech]

Was sure I was going to be able to resolve this, but

Bought 2005 E53 3.0 used (144k mi) in March with known bad aux fan (would not command on with Schwabben/510 tool). Replaced the aux fan while I went through & changed fluids, plugs, filters, (complete cooling system refresh), etc.
- New fan will activate for 30 sec & shut off per tool command.
- Compressor will also activate for 30 sec & shut off per tool command.
- Had AC system vacuum tested & checked for proper capacity (i.e. no leaks)
- AC will not kick on or run cold while idling
- AC will sometimes run cold after driving a bit, then on & off
- Still getting code for DME: Activation electric fan (but can activate via tool)

Along the way, scoured many forum posts, YouTube clips etc. & replaced the following:
- Aux fan sensor switch (when I put the new fan in)
- HVAC control panel from Ebay (12 pin)
- evap temp sensor (original was corroded)
- blower motor resistor (while I was there)
- Have checked & swapped all fuses, including 60A on backside of glovebox fuse panel
- Have cleaned & reseated plugs on AC hi/low pressure switches

Never got ISTA to connect in spite of three load/configure attempts, so don't have much in the way of diagnostic data. This is particularly frustrating as I design/test/troubleshoot software for a living. Stopped short of buying another OBD2-USB cable & starting over.

I'm hesitant to hit a generic auto shop, as most don't seem to know these BMW systems well. Haven't found a great local shop & do almost all my own work. Was thinking of going to Kassel Performance in York, PA (great experience with my X35D tune, etc.) but they said they aren't AC experts.

I'm in Southern MD in the NCC & X chapters of BMW CCA