I have a pretty old AC that is currently losing freon at an alarming
rate. I was planning on replacing anyway, so started getting quotes
immediately this summer.

The first 3 estimates all suggested 3 ton units. The last one
suggested 2.5. Half suggested running a totally new coolant line, and
half suggested reusing most of the existing line. So, I have a couple
questions for a third party audience..

1) To determine size all of the contractors measured the intakes and
ventilation coming off of the blower. A few asked for my approx sq
footage, and a few paid close attention to the size of the current (28
year old) unit. The last guy I had over was the one that went with
the 2.5 ton estimate, and he explained it was because my intake did
not allow for anything bigger, and that my blower was a 3ton and it
was best to go with a larger blower. He did say this seemed slightly
underpowered for my 1800sqft house, but that it was much better than
oversizing causing humidity issues and the coils freezing over. Does
it sound like the last guy knew what he was talking about?

2) As I said, our current unit was leaking, and its not clear where
that's going on. There's a small possibility the previous owner
nicked the line when finishing the basement ceiling, but this seems
unlikely since he did a couple years ago and the problem didn't get
too bad until this summer. So, some of these guys think we should
replace the whole thing, by running it under my deck and alongside the
house a bit to avoid ripping up drywall (I really don't want to
destroy). The last guy said he'd prefer to hack off just the part
that's currently exposed, and re solder a new piece to it, then
pressure test the lines. He' says he should be able to discount the
ceiling leak that way. Does this sound reasonable?

Any help you can provide would be great. I'm just not sure what to do
with the conflicting opinions.

Thanks,
FW