Our A/C evaporator coil freeze up last year, so I called out a technician.
He said that it was charged with the proper amount of Freon, and my problem [paraphrased] "something had narrowed the inside of the coil", and said that "cleaning the coil would be a waste of money since that would cost ~$900 (uncharge, take out, clean, reinstall, recharge), and a new A/C is only $1800".
My BS alarm was going off at the time and I'm going to get a second opinion, but in the mean time:
Q1: Can a coil go bad in the manner he described?
Q2: I know in the system there should be only Freon and lubricating oil, but can you figure out if there's any contaminates ?