Is there a junction box in the attic? If there is disconnect the wire from the box. If there is not, terminate the wire in a new junction box. Nail it to a joist so that is out of the way. Place a wire nut on the black and white wires.

The national average for replacing AC systems is around 15 years or so. They don't break this down into builder grade or non-builder grade. I can tell you from a repair perspective builder grade units aren't any more prone to breakage or replacement than non-builder grade unit. If I was going to classify something as builder grade I would merely say 'entry level' system.... with no bells and whistles. That means 13 / 14 SEER in the North and 14 SEER in the South. The name on the side of the unit matters little. I've repaired all brands in this realm just as much as I've replaced them. What's different about my area is 'use'. I live in a hot climate, so if anything is going to fail prematurely it was going to do it regardless of the name on the side of the unit. Running something 10 months out of the year in comparison to a climate that might use it 3 or 4 months (not that this is the case of the OP) --- just so you know there is much more to think about other than the name on the side of the unit. If you jump up out of the builder grade closet, your install cost is going to go up. A builder 'may' not be that well suited installing something other than 'a builder grade unit'. Why? Because a builder typically doesn't have the experience of doing this sort of thing correctly. It's like the added bells and whistles of zone systems. --- Most of these I come across in new builds are generally garbage, don't work right and due to 'design' of them there's no way they could work right. You have to realize a builder has a small skill set, because they are always working with something that is 'new' out of the box from the store. They rarely see a broken system... whether it's builder grade or not. Most builders in the HVAC realm 99% do not run HVAC service. They simply are not built for it. Definition of HVAC service is: 7am - 7pm Sunday Thru Saturday. Not 8-5 Mon-Fri. Not leave a message at the beep, not we'll get back to you within 72 hours, etc. With that said some claim to offer service in this regard, but fall considerably short. Maybe you need it, maybe you don't. In a hot climate like mine? Don't kid yourself. Remember a builder builds. So if they tell you they don't have problems with xyz brand it's probably that it doesn't have problems with in the year or two that they are on the hook to fix it. There are plenty of builder horror stories on this board to prove what I say is accurate. So to say the answer is to install better than builder grade system, you better hope they have the skill set to install it properly or it's sure to give you even more trouble. There is no warranty coverage for improper installation, builder's go out of business all the time, so keep that in mind as well. 25% of the knowledge needed to install an AC system. The other 75% is knowing what not to do.

Again, we shouldn't be second-guessing any of this based on incomplete information, misinformation from the homeowner, etc. We haven't done a Manual J, we haven't seen a floorplan, determined solar gain, or any other really important info. We are guessing. We are also encouraging a homeowner to be involved in a way that will most certainly muddle roles and responsibilities on a project that's in trouble as it is. This is a setup for failure - and none of us are going to be around when this goes South. OP: You are asking strangers- who may or may not be qualified- questions that require accurate and complete facts in order to engineer a solution. You have a desired outcome in your head, and you are fishing around on the internet for someone to validate your ideas. Stop it. Tell the person who is in charge of this project (not the HVAC guy) to figure all of this out and get a qualified HVAC contractor in there. Your role as the owner is not to design the HVAC - and you put the entire project in jeopardy when you blur roles and responsibilities. The HVAC contractor doesn't work for you, he works for the GC. If I were associated with this job, and you came to me saying that you and your internet buddies have decided how the ductwork should be... I'd tell you exactly where to stick your laptop before I walked off the job.

Thanks to all of you for your comments and the education it is providing me. HVAC is clearly an area where ideally I'd be able to "leave it to the professionals" and take the advice of a trusted professional. Unfortunately after working with a firm for 10 years (installations at two houses) they installed a heat pump incorrectly, and that did not meet my visibility or loudness requirements (other units were available but they did not offer them) - and they were unwilling to change the system or make other concessions after the installation. So this time I'm getting educated and aiming to be very clear in the requirements that I give to whichever contractor I pick. BTW, while I am focusing on the condenser I am replacing, we will also be moving the heat pump air handler near the condenser, both near those bedroom windows. With the issues Austin brought up about the 24VNA9 unit, the 24ANB6 (66 db) and 24APB6 (68db) are attractive. Any issues with using the Infinity 24ANB6 with a Performance 59TP6B 2 stage furnace and CNPVP coil? I "hear" your concerns about putting the condenser and air handler near bedrooms. The alternative (where they are now) is on the street side of the house and unattractive both from the street and looking out the sunroom window next to them. I will likely rig a test with my stereo and play "white noise" at 68 to 70 db where the units may be installed near bedrooms and see what it sounds like from inside the bedrooms. I also recognize a big issue is the turn-on noise, which I won't be able to simulate. I will plan on investing in a sound blanket both for the condenser and for the air handler. That seems like all I can do to minimize the noises. Again, thank you all for your inputs, Bob C