The unit was manufactured in October of 1986 and still works properly, but it is getting REAL old. I'd like to start getting prices on a replacement unit, but I don't know what size (in tons) it is. Can you help me?

Not sure which number to use, but is a number divisable by 6(half ton)
The 30 in the number would be 5, 1/2 tons, or 2.5 tons.
AC guys may say 12 per ton, and 6 left over would be a half ton?

Yep, 30 is the number you are looking at in the model. It is a two and a half ton unit.