I have a 1300 square foot house, with a new furnace, and an installed A-coil. I was recommended to purchase a 2.5 or 3 ton AC unit. I have an opportunity to purchase a 5 ton for little to nothing. Can this work? The 5 ton is a Gibson, used only 1 year and professionally removed from the business.

No,, 5 ton is way to big,, it would cause nothing but problems even if you had a 5 ton evap.coil which you would have to have,, will cause much mold and mildew in your home,, rot the wood,cause the paint to fall off,, and who knows what else

Agree with wmproop. Oversizing an ac unit is a big no no. And the condenser must match the a-coil on top of the furnace. When the new furnace and a-coil were installed they were most likely sized for the home, so you will need to get the correct size outside condenser to match the a-coil.