How to operate AC with dead radio/display? (Grand Cherokee Overland 2014)

My factory radio/display is currently disconnected from the battery because it was determined by the dealer techs to be the cause of a parasitic electrical draw that was draining the battery. That radio is still physically installed, but the techs disconnected the grey wire from the battery terminal under the seat to stop the battery drain. I'm awaiting delivery of a used radio that I bought online later this week.
But it's been hot, so in the meantime I tried running the AC with the manual controls - it runs for about 30 seconds, but then the amber lights on both the front and rear defroster buttons light up, as does the AC button light, the vent blower shuts off, and all of the manual buttons become unresponsive. It locks up in this mode.
Is there any way to stop this lock up from happening so that I can properly operate the AC with the manual controls with a dead / disconnected radio?