Quick question. I have an old trane 4.25 ton open system that I'm replacing with a new 4 ton geocool. I have the unit and noticed that it has 1 inch npt fitting but my old unit has 3/4 inch and my whole house is plumbed with 3/4. Can I increase my pipe size at the unit and step it back down coming out without negatively affecting the unit or do I need an entire new line put in the house?

The 1" connection on the new unit is typical for closed loop systems where minimizing pump head is a concern. With your open loop 3/4 piping should be fine especially if it worked with your old unit.