I am having the EXACT problem. I am not as technically say as you, but I don’t want to be bent over the hood by a dealer or shop. Summer in southern Colorado. Parked in the sun the past few days. Drove it to town this AM and it stopped getting cool within a few minutes. I happened to be parked in the shade for 1/2 hour and boom! Ice cold. Parked it at home, under the shade tree with the engine still running and checked under the hood. All fans running, no indication of icing (that I could see.) This has happened off and on since I bought the car last fall from my son.
ANY help would be greatly appreciated.