Okay, a couple of weeks ago, I bring in my car to get some regular maintenance done on it i.e. oil change. After I paid the bill, I headed outside to reclaim my vehicle. As I got in to start the car up, I noticed that my a/c was on the highest setting, even before I turned it on. This has happened before. Anyone know the reason why this is even done? 
They were probably testing various systems so they could find one tiny thing wrong. Then when you returned, they could insist that it needed to be fixed right away at $50/hr.
When I went for Virginia vehicle inspections, they almost always found one light bulb out. Then they’d offer to fix it for $20, charge me $1 for the re-inspection, and give me a pass. Instead, I’d find an auto parts store, buy the $1.50 bulb, fix it, then go for the re-inspection. Saved $19, and pissed off the garage guy.
Maybe it was hot in the car?
Any dealer worth his salt would put the customers car back the way it was when it came in. Find another dealer.
You live in New Orleans, it’s the middle of summer. did you expect the guy who got into your car after being parked in the sun to turn on the heater?
Of course he turned on the A/C, your car was as hot as a sauna.
While the dealer should have returned your car with everything as was, running the AC would be on a checklist of maintenance items to look at (not knowing what you took it in for). If they looked at the head pressure of the AC, it would have to be running.
An aside: it’s a good idea to run your AC once a month regardless of how cold it is. This helps keep the seals lubed and prevents them from drying out and collapsing.
Maybe it’s like the car wash. They wipe down the dash and inevitably knock the setting all the way to one side.
I did that last year. One of my turn signal lights was burned out. The guy at the dealership offered to replace it for a high fee. I told him I’d just walk across the street to Auto Zone and get one and replace it myself. He told me that that would void my cars warranty. He made me laugh so hard.
When I lived in Virginia and they had vehicle inspection, the scam was head light alignment. Not only did they charge you for alignment, half the time they screwed it up so bad you had to take it somewhere else to get it fixed so you could drive at night.
It may be what Chefguy was saying about it being on a checklist of things to look for. I know, that even when it gets really hot here – and it does! – that I still never put the A/C on the highest setting. The second one does fine enough. 
…along with any loose change on your dash.
I had always heard this in the olden days. But Click & Clack informed me a few years ago that modern cars switch on the compresser when the AC switch is set to “defrost.” That way, the system gets used in the winter wherever you are.
A comment that, if made by a dealership in Australia, could have cost the dealership a fine of anything up to a few million dollars on a second offence.
Just to follow this tangent, I’ve lived in Virginia for eight years with two cars. That’s 16 inspections, and I’ve never once had a place tell me that I needed any work at all (except for emissions, that’s a different story).