I took it to a local place (since I didnt want to drive 30 miles and explode).
They put about 1 gallon of dex+distilled, so I am hoping that was the cause.
Although I would have thought that the 'low coolant' warning would turn on before the coolant got to a level that required the AC to have to be turned off
Anyway hope its fixed, I will get it serviced by a GM dealer in the next few weeks just to be sure.