As more info. is being released, I'm getting more confused. You said in the original thread that you had 28 yr. old a 2.5 ton A/C.

Now we find out that that did the entire house? My post #16 asked some questions that might help us understand alittle better.

But, never oversize. The explaination (reason) the HVAC guy as to why he wanted to install a 3 ton is insane.