See photos attached. Anyone know why this unit looks like it has hot spots?
To be honest I have never seen that pattern before and I have worked on them most of my life.
The only thing I can think of is at some time the condenser fan quit working and someone hung that garden hose on the unit at let it run. That is just a wild guess
Yup, same here. I’ve never seen anything like this before nor can I offer a reasonable explanation for its existence other than it it is most likely the result of external sources such as Charley posted.
The geeky kid next door built a powerful laser?
Did they have large dog(s)? 
They might be pee stains. The oxidation effect on copper might have caused this. The dog(s) may have been peeing on it for a while for this to happen. Just a guess.
It looks like some type of attached mechanical device to help with cooling , perhaps the fan motor failed at one time and was a make shift fix. Or perhaps someone built a box over for sound . Just a guess .
Another guess would be if the home owner decided to service the unit himself/herself and sprayed the unit with some industrial type of power spray which left the marks.
I am not even sure if that is any method to clean the unit but I am just guessing again.
Hydrofloric Acid will make it like new (without the paint)!
Was this a Heat pump? Perhaps someone thought de- icing with a Pan heater. some what like this http://compare.ebay.com/like/370555737769
Just a thought
If you look looks like a cord was attached to what ever it was, Coils flatten