1) You have a post-1996 850 (ie, OBD plugs in rt. above shift lever)?
2) You've gotten NO fault code from a/c (ie, the "a/c On" and the "Rec" lights flash for 20 sec)?
The good news is that it sounds electrical to me.

You removed probably the a/c relay behind the glovebox. My best educated guess (emphasize GUESS) is that there's a problem w/ the E. Climate Control POWER STAGE -- aka, "ECC Output (Power) Stage." This is located beside a/c relay, behind glovebox.

A faulty actual fan SWITCH/rheastat would, I think?, trigger a fault code, but the Power Stage to my knowledge doesn't necessarily do so.
What I definitely do NOT know is whether a screwy Power Stage would 100% affect compressor's function. I suspect it would.
3) (Have you tried to apply power directly to compressor?)
4) I guess you've tried all possible combinations to try to get fan off. Have you tried these . . . This is grabbin' at straws:
*tried fan switch on AUTO and through entire range of MANUAL? Try both of those with these combos:
*tried fan switch with a/c OFF and temps turned all the way to Hot
* " " " " " " " " " " " and defrost ON