Feli,

The lineset is the pair of copper tubes which connect the indoor coil to the outside condenser. The condensate drain line drains the water produce by the furnace. It is usually connected to a condensate pump or connected to a drain in the house.

I have a similar situation as yours. My house has two Infinity sytems, one for each floor. My upstairs unit was an old Carrier 2 ton condenser. The manual J calculation for upstairs (bedrooms and bathrooms) came out to 2.4 tons. The Carrier dealer suggested either the Peformance 2.5 ton, or the Infinity 3 ton. The 3 tone Infinity cost $600 extra. I told the contractor I was worried about going to 3 tons since the 2 tons seems to cool OK (I tend to keep the thermostat higer than most people, 78-79). He refused to do 2 ton, and told me the 2.5 single or 3 ton 2-stage would be fine. I reluctantly paid the extra money and went with the 3 ton unit with a 4 ton coil.

I am happy I made this choice. The humidity has been as low as 38%. I usually set the upstairs back to about 82 degrees during the day, and cool it down to 79 after 6 pm. The unit can quickly cool the upper floor and still maintain a low humidity level.

There is nothing wrong with the Carrier Performance 2.5 single stage condenser. However the Infinity 2-stage is nicer. If you do 2-stages you will need to move up to 3 tons. You should not have a problem if your duct work has been correctly sized.

So is the lineset different from the "refrigerant piping between the evaporator and outside unit"?

"refrigerant piping between the evaporator and outside unit"

This is the lineset.

I prefer that linesets be replaced.

But if re-used, it mush be flushed to SOP, and it must be size that manufacturer recommends on the new outside condenser. Evap coil also should be a match and the best match.

Unfortunately, these are areas where some dealers try to take shortcuts at the homeowners expense.

IMO