I'm not familiar with the non IHKA (auto temp) set up, but it sounds like it's not seeing or liking something. If you can work all the outputs through IMPA but still have no air there must be an input missing.

You could try pulling the lower rad hose temp sensor and see if the DME turns on the aux fan just to see if it has some control of it.

You could also try defrost to see if that kicks the compressor in.

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