Weird A/C issue

[Buckeyexx]

So here is my issue. I recently sold my camper because I wasn’t using it as much as I would have liked. The couple that bought it paid for it about a month ago and I have kept it stored for them since then. Well they decided to come pick it up this past weekend while the weather has been a little better. Had lots of snow on top of the camper.
I back it into the shop I work in so I can hook it up to power while I go over a few things with them.
While we were sitting there talking I start smelling something electrical getting hot. Before we could even react we heard something pop and lost all power to camper. I thought ok tripped a circuit somehow so I go check the plug and the breakers inside and found nothing had tripped. Unplugged from the outlet and plugged back in and everything came back up as a if nothing had happened. The smell had gone away at this point but I kept on looking for what had happened. When got to the ac unit to see if it would turn on it would not. It was never on at all and didn’t want to turn it on with the snow on top.
So here is my question. What could have caused something to burn up inside the ac unit when I didn’t have it on? All I did was plug in the camper but never tried operating the ac unit. I checked Everything else works inside and it does.
Luckily I transferred my extended warranty over to the new owners but I hate that this could happen to them already. Sorry for the long post!