Check your coolant level? should be at full mark with engine cold/turned off and parked on level ground. Wouldn't hurt to add an inch or two of the correct coolant even so, to see if the level goes down any and if the problem resolves.
They ran dye through the HVAC, and nothing was found? Is it assumable that the refrigerant level is OK? You can track AC status & pressures with Forscan, haven't checked with Torque. I see refrigerant pressures around 600 kPa when off and up to 1700 kPa when on full blast.
Sometimes the AC pressure switch does fail. Or the Schrader valve in the ports for the Hi and/or Lo sides gets stuck, so a fill/fill level indication is incorrect.