Matt Man....
Sadly -- my life is so "gone" that all I can do is hang on this site...
Hey --- seriously. The A/C shop should not concern itself with the ISIS. They only need to know the compressor is getting it's 12V+
Actually - sounds to me like it might be a "THERMOSTAT" issue... did you try changing the temp setting? Can you control the airflow? I.E., Defrost - heat - a/c etc. Then you'd know the unit is working the doors/air controllers... then cycle the heat and cold temp switch - see if you can get heat and heat to the defroster... after that -- it would seem you have an issue with the compressor clutch and or the trinary switch.
I always left the clutch control wire disconnected when my units aren't charged -- just to make sure I (or someone) didn't accidentally turn the thing on. So maybe look at the wiring on the trinary switch to see that all four are connected. After that... I'd be taking it to the shop and let D!ck figure it out cause we won't be able to do that from the forum.